{ "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-2026-26209", "tracking": { "current_release_date": "2026-03-26T12:43:02.276212Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-26209", "initial_release_date": "2026-03-24T13:50:45.710290Z", "revision_history": [ { "date": "2026-03-24T13:50:45.710290Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (4).| CWES updated (1)." }, { "date": "2026-03-24T13:50:54.942723Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-03-24T14:25:06.533882Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| Products created (1).| References created (4).| CWES updated (1)." }, { "date": "2026-03-24T14:25:14.382232Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-03-24T20:42:29.757244Z", "number": "5", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (21).| Product Identifiers created (4).| References created (6).| CWES updated (1).| Vendor_assessment created." }, { "date": "2026-03-24T20:42:38.892414Z", "number": "6", "summary": "NCSC Score updated." }, { "date": "2026-03-24T20:53:47.433141Z", "number": "7", "summary": "Unknown change." }, { "date": "2026-03-24T21:50:17.523786Z", "number": "8", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-03-25T01:00:27.597383Z", "number": "9", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (4).| CWES updated (1)." }, { "date": "2026-03-25T01:00:32.654978Z", "number": "10", "summary": "NCSC Score updated." }, { "date": "2026-03-25T18:26:36.308454Z", "number": "11", "summary": "Products connected (1).| Product Identifiers created (1).| Exploits created (1)." }, { "date": "2026-03-25T18:26:45.316824Z", "number": "12", "summary": "NCSC Score updated." }, { "date": "2026-03-25T18:36:54.629381Z", "number": "13", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (40).| Product Identifiers created (40).| Products created (1).| References created (3).| CWES updated (1)." }, { "date": "2026-03-25T21:01:57.826010Z", "number": "14", "summary": "References created (2)." }, { "date": "2026-03-26T00:38:38.321983Z", "number": "15", "summary": "References created (2)." }, { "date": "2026-03-26T12:42:58.593513Z", "number": "16", "summary": "Source created.| CVE status created. (valid)| Description created for source.| Products connected (2)." }, { "date": "2026-03-26T12:43:01.431244Z", "number": "17", "summary": "NCSC Score updated." } ], "status": "interim", "version": "17" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:rpm/3", "product": { "name": "vers:rpm/3", "product_id": "CSAFPID-2858641", "product_identification_helper": { "cpe": "cpe:/a:redhat:ai_inference_server:3" } } } ], "category": "product_name", "name": "Red Hat AI Inference Server" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/2", "product": { "name": "vers:rpm/2", "product_id": "CSAFPID-1508257", "product_identification_helper": { "cpe": "cpe:/a:redhat:ansible_automation_platform:2" } } } ], "category": "product_name", "name": "Red Hat Ansible Automation Platform 2" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/3", "product": { "name": "vers:rpm/3", "product_id": "CSAFPID-5198605", "product_identification_helper": { "cpe": "cpe:/a:redhat:enterprise_linux_ai:3" } } } ], "category": "product_name", "name": "Red Hat Enterprise Linux AI (RHEL AI) 3" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-1439279", "product_identification_helper": { "cpe": "cpe:/a:redhat:openshift_ai" } } } ], "category": "product_name", "name": "Red Hat OpenShift AI (RHOAI)" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5206383" } } ], "category": "product_name", "name": "bootc-aws-cuda-rhel9" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5206384" } } ], "category": "product_name", "name": "bootc-azure-cuda-rhel9" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5811347" } } ], "category": "product_name", "name": "bootc-azure-rocm-rhel9" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5205180" } } ], "category": "product_name", "name": "bootc-cuda-rhel9" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5198606" } } ], "category": "product_name", "name": "bootc-gcp-cuda-rhel9" }, { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-5811351" } } ], "category": "product_name", "name": "bootc-rocm-rhel9" } ], "category": "product_family", "name": "Red Hat Enterprise Linux AI (RHEL AI) 3" }, { "branches": [ { "branches": [ { 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"category": "product_family", "name": "bookworm" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:deb/unknown", "product": { "name": "vers:deb/unknown", "product_id": "CSAFPID-5195301" } } ], "category": "product_name", "name": "cbor2" } ], "category": "product_family", "name": "bullseye" } ], "category": "vendor", "name": "Debian" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/1.0.0", "product": { "name": "vers:unknown/1.0.0", "product_id": "CSAFPID-3931679", "product_identification_helper": { "purl": "pkg:pypi/cbor2@1.0.0" } } }, { "category": "product_version_range", "name": "vers:unknown/1.1.0", "product": { "name": "vers:unknown/1.1.0", "product_id": "CSAFPID-3931680", "product_identification_helper": { "purl": "pkg:pypi/cbor2@1.1.0" } } }, { "category": "product_version_range", "name": "vers:unknown/2.0.0", "product": { "name": "vers:unknown/2.0.0", "product_id": "CSAFPID-3931681", "product_identification_helper": { "purl": "pkg:pypi/cbor2@2.0.0" } } }, { "category": "product_version_range", "name": "vers:unknown/3.0.0", "product": { "name": "vers:unknown/3.0.0", "product_id": "CSAFPID-3931682", "product_identification_helper": { "purl": "pkg:pypi/cbor2@3.0.0" } } }, { "category": "product_version_range", "name": "vers:unknown/3.0.1", "product": { "name": "vers:unknown/3.0.1", "product_id": "CSAFPID-3931683", "product_identification_helper": { "purl": "pkg:pypi/cbor2@3.0.1" } } }, { "category": "product_version_range", "name": "vers:unknown/3.0.2", "product": { "name": "vers:unknown/3.0.2", "product_id": "CSAFPID-3931684", "product_identification_helper": { "purl": "pkg:pypi/cbor2@3.0.2" } } }, { "category": "product_version_range", "name": "vers:unknown/3.0.3", "product": { "name": "vers:unknown/3.0.3", "product_id": "CSAFPID-3931685", "product_identification_helper": { "purl": "pkg:pypi/cbor2@3.0.3" } } }, { "category": "product_version_range", "name": "vers:unknown/3.0.4", "product": { "name": "vers:unknown/3.0.4", "product_id": "CSAFPID-3931686", "product_identification_helper": { "purl": "pkg:pypi/cbor2@3.0.4" } } }, { "category": "product_version_range", "name": "vers:unknown/4.0.0", "product": { "name": "vers:unknown/4.0.0", "product_id": "CSAFPID-3931687", "product_identification_helper": { "purl": "pkg:pypi/cbor2@4.0.0" } } }, { "category": "product_version_range", "name": "vers:unknown/4.0.1", "product": { "name": "vers:unknown/4.0.1", "product_id": "CSAFPID-3931688", "product_identification_helper": { "purl": "pkg:pypi/cbor2@4.0.1" } } }, { "category": "product_version_range", "name": "vers:unknown/4.1.0", "product": { "name": "vers:unknown/4.1.0", "product_id": "CSAFPID-3931689", "product_identification_helper": { "purl": "pkg:pypi/cbor2@4.1.0" } } }, { "category": "product_version_range", "name": "vers:unknown/4.1.1", "product": { "name": "vers:unknown/4.1.1", "product_id": "CSAFPID-3931690", "product_identification_helper": { "purl": "pkg:pypi/cbor2@4.1.1" } } }, { "category": "product_version_range", "name": "vers:unknown/4.1.2", "product": { "name": "vers:unknown/4.1.2", "product_id": "CSAFPID-3931691", "product_identification_helper": { "purl": "pkg:pypi/cbor2@4.1.2" } } }, { "category": "product_version_range", "name": "vers:unknown/5.0.0", "product": { "name": "vers:unknown/5.0.0", "product_id": "CSAFPID-3931693", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.0.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.0.1", "product": { "name": "vers:unknown/5.0.1", "product_id": "CSAFPID-3931694", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.0.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.1.0", "product": { "name": "vers:unknown/5.1.0", "product_id": "CSAFPID-3931695", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.1.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.1.1", "product": { "name": "vers:unknown/5.1.1", "product_id": "CSAFPID-3931696", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.1.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.1.2", "product": { "name": "vers:unknown/5.1.2", "product_id": "CSAFPID-3931697", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.1.2" } } }, { "category": "product_version_range", "name": "vers:unknown/5.2.0", "product": { "name": "vers:unknown/5.2.0", "product_id": "CSAFPID-3931698", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.2.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.2.0.post1", "product": { "name": "vers:unknown/5.2.0.post1", "product_id": "CSAFPID-5317854", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.2.0.post1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.3.0", "product": { "name": "vers:unknown/5.3.0", "product_id": "CSAFPID-3931699", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.3.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.0", "product": { "name": "vers:unknown/5.4.0", "product_id": "CSAFPID-3931700", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.1", "product": { "name": "vers:unknown/5.4.1", "product_id": "CSAFPID-3931701", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.2", "product": { "name": "vers:unknown/5.4.2", "product_id": "CSAFPID-3931702", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.2" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.2.post1", "product": { "name": "vers:unknown/5.4.2.post1", "product_id": "CSAFPID-3931703", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.2.post1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.3", "product": { "name": "vers:unknown/5.4.3", "product_id": "CSAFPID-3931704", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.3" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.4", "product": { "name": "vers:unknown/5.4.4", "product_id": "CSAFPID-3931705", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.4" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.5", "product": { "name": "vers:unknown/5.4.5", "product_id": "CSAFPID-3931706", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.5" } } }, { "category": "product_version_range", "name": "vers:unknown/5.4.6", "product": { "name": "vers:unknown/5.4.6", "product_id": "CSAFPID-3931707", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.4.6" } } }, { "category": "product_version_range", "name": "vers:unknown/5.5.0", "product": { "name": "vers:unknown/5.5.0", "product_id": "CSAFPID-3931708", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.5.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.5.1", "product": { "name": "vers:unknown/5.5.1", "product_id": "CSAFPID-1640791", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.5.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.0", "product": { "name": "vers:unknown/5.6.0", "product_id": "CSAFPID-1075813", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.1", "product": { "name": "vers:unknown/5.6.1", "product_id": "CSAFPID-1075814", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.2", "product": { "name": "vers:unknown/5.6.2", "product_id": "CSAFPID-5315933", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.2" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.3", "product": { "name": "vers:unknown/5.6.3", "product_id": "CSAFPID-5315934", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.3" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.4", "product": { "name": "vers:unknown/5.6.4", "product_id": "CSAFPID-5315935", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.4" } } }, { "category": "product_version_range", "name": "vers:unknown/5.6.5", "product": { "name": "vers:unknown/5.6.5", "product_id": "CSAFPID-5315936", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.6.5" } } }, { "category": "product_version_range", "name": "vers:unknown/5.7.0", "product": { "name": "vers:unknown/5.7.0", "product_id": "CSAFPID-5315937", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.7.0" } } }, { "category": "product_version_range", "name": "vers:unknown/5.7.1", "product": { "name": "vers:unknown/5.7.1", "product_id": "CSAFPID-5315938", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.7.1" } } }, { "category": "product_version_range", "name": "vers:unknown/5.8.0", "product": { "name": "vers:unknown/5.8.0", "product_id": "CSAFPID-5494080", "product_identification_helper": { "purl": "pkg:pypi/cbor2@5.8.0" } } }, { "category": "product_version_range", "name": "vers:unknown/<5.9.0", "product": { "name": "vers:unknown/<5.9.0", "product_id": "CSAFPID-5900044", "product_identification_helper": { "cpe": "cpe:2.3:a:agronholm:cbor2:*:*:*:*:*:python:*:*" } } }, { "category": "product_version_range", "name": "vers:unknown/>=0|<5.9.0", "product": { "name": "vers:unknown/>=0|<5.9.0", "product_id": "CSAFPID-5908032" } } ], "category": "product_name", "name": "cbor2" } ], "category": "vendor", "name": "agronholm" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-26209", "cwe": { "id": "CWE-674", "name": "Uncontrolled Recursion" }, "notes": [ { "category": "description", "text": "cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format. Versions prior to 5.9.0 are vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures. This vulnerability affects both the pure Python implementation and the C extension `_cbor2`. The C extension relies on Python's internal recursion limits `Py_EnterRecursiveCall` rather than a data-driven depth limit, meaning it still raises `RecursionError` and crashes the worker process when the limit is hit. While the library handles moderate nesting levels, it lacks a hard depth limit. An attacker can supply a crafted CBOR payload containing approximately 100,000 nested arrays `0x81`. When `cbor2.loads()` attempts to parse this, it hits the Python interpreter's maximum recursion depth or exhausts the stack, causing the process to crash with a `RecursionError`. Because the library does not enforce its own limits, it allows an external attacker to exhaust the host application's stack resource. In many web application servers (e.g., Gunicorn, Uvicorn) or task queues (Celery), an unhandled `RecursionError` terminates the worker process immediately. By sending a stream of these small (<100KB) malicious packets, an attacker can repeatedly crash worker processes, resulting in a complete Denial of Service for the application. Version 5.9.0 patches the issue.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-26209" }, { "category": "description", "text": "cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format. Versions prior to 5.9.0 are vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures. This vulnerability affects both the pure Python implementation and the C extension `_cbor2`. The C extension relies on Python's internal recursion limits `Py_EnterRecursiveCall` rather than a data-driven depth limit, meaning it still raises `RecursionError` and crashes the worker process when the limit is hit. While the library handles moderate nesting levels, it lacks a hard depth limit. An attacker can supply a crafted CBOR payload containing approximately 100,000 nested arrays `0x81`. When `cbor2.loads()` attempts to parse this, it hits the Python interpreter's maximum recursion depth or exhausts the stack, causing the process to crash with a `RecursionError`. Because the library does not enforce its own limits, it allows an external attacker to exhaust the host application's stack resource. In many web application servers (e.g., Gunicorn, Uvicorn) or task queues (Celery), an unhandled `RecursionError` terminates the worker process immediately. By sending a stream of these small (<100KB) malicious packets, an attacker can repeatedly crash worker processes, resulting in a complete Denial of Service for the application. Version 5.9.0 patches the issue.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/26xxx/CVE-2026-26209.json" }, { "category": "description", "text": "A flaw was found in cbor2, a library for encoding and decoding Concise Binary Object Representation (CBOR) data. A remote attacker can exploit this vulnerability by sending a specially crafted CBOR payload containing deeply nested structures. This can cause the application to crash due to uncontrolled recursion, leading to a complete Denial of Service (DoS) for the affected application.", "title": "redhat - https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-26209.json" }, { "category": "description", "text": "### Summary\n\n- The `cbor2` library is vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures.\n- This vulnerability affects both the pure Python implementation and the C extension (`_cbor2`). The C extension correctly uses Python's C-API for recursion protection (`Py_EnterRecursiveCall`), but this mechanism is designed to prevent a stack overflow by raising a `RecursionError`. In some environments, this exception is not caught, thus causing the service process to terminate.\n- While the library handles moderate nesting, it lacks a configurable, data-driven depth limit independent of Python's global recursion setting. An attacker can supply a crafted CBOR payload containing thousands of nested arrays (e.g., `0x81`). When `cbor2.loads()` attempts to parse this, it hits the interpreter's recursion limit, causing the call to raise a `RecursionError`.\n- By sending a stream of small (<100KB) malicious packets, an attacker can repeatedly crash worker processes faster than they can be restarted, resulting in a complete and sustained Denial of Service.\n\n### Details\n\n- The vulnerability stems from the recursive design of the `CBORDecoder` class, specifically how it decodes nested container types like Arrays and Maps.\n- Inside `decode_array` (and similarly `decode_map`), the decoder iterates through the number of elements specified in the CBOR header. For each element, it calls `self.decode()` again to parse the nested item. This recursive call lacks a depth-tracking mechanism.\n- Vulnerable Code Locations:\n - `cbor2/decoder.py` (Pure Python implementation)\n - `source/decoder.c` (C extension implementation)\n- Execution Flow:\n 1. The `cbor2.loads()` function initializes a `CBORDecoder` and calls its `decode()` method.\n 2. The `decode()` method reads the initial byte and dispatches control to a specific handler based on the major type. For an Array (Major Type 4), it calls `decode_array`.\n 3. `decode_array` loops and calls `self.decode()` for each item, leading to deep recursion when parsing a payload like `[...[...[1]...]...]`.\n\n### PoC\n\n```\nimport cbor2\n\nDEPTH = 1000\n\npayload = b'\\x81' * DEPTH + b'\\x01'\nprint(f\"[*] Payload size: {len(payload) / 1024:.2f} KB\")\nprint(\"[*] Triggering decoder...\")\n\ntry:\n cbor2.loads(payload)\n print(\"[+] Parsed successfully (Not Vulnerable)\")\nexcept RecursionError:\n print(\"\\n[!] VULNERABLE: RecursionError triggered!\")\nexcept Exception as e:\n print(f\"\\n[-] Unexpected Error: {type(e).__name__}: {e}\")\n```\n\n### Impact\n\n- Scope: This vulnerability affects any application using `cbor2` to parse untrusted data. Common use cases include IoT data processing, WebAuthn (FIDO2) authentication flows, and inter-service communication over COSE (CBOR Object Signing and Encryption).\n- Attack Vector: A remote, unauthenticated attacker can achieve a full Denial of Service with a highly efficient, low-bandwidth attack. A payload under 100KB is sufficient to reliably terminate a Python worker process.\n\n### Credit\n\nThis issue was discovered by Kevin Tu of TMIR at ByteDance. The patch was developed by @agronholm.", "title": "github - https://api.github.com/advisories/GHSA-3c37-wwvx-h642" }, { "category": "description", "text": "### Summary\n\n- The `cbor2` library is vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures.\n- This vulnerability affects both the pure Python implementation and the C extension (`_cbor2`). The C extension correctly uses Python's C-API for recursion protection (`Py_EnterRecursiveCall`), but this mechanism is designed to prevent a stack overflow by raising a `RecursionError`. In some environments, this exception is not caught, thus causing the service process to terminate.\n- While the library handles moderate nesting, it lacks a configurable, data-driven depth limit independent of Python's global recursion setting. An attacker can supply a crafted CBOR payload containing thousands of nested arrays (e.g., `0x81`). When `cbor2.loads()` attempts to parse this, it hits the interpreter's recursion limit, causing the call to raise a `RecursionError`.\n- By sending a stream of small (<100KB) malicious packets, an attacker can repeatedly crash worker processes faster than they can be restarted, resulting in a complete and sustained Denial of Service.\n\n### Details\n\n- The vulnerability stems from the recursive design of the `CBORDecoder` class, specifically how it decodes nested container types like Arrays and Maps.\n- Inside `decode_array` (and similarly `decode_map`), the decoder iterates through the number of elements specified in the CBOR header. For each element, it calls `self.decode()` again to parse the nested item. This recursive call lacks a depth-tracking mechanism.\n- Vulnerable Code Locations:\n - `cbor2/decoder.py` (Pure Python implementation)\n - `source/decoder.c` (C extension implementation)\n- Execution Flow:\n 1. The `cbor2.loads()` function initializes a `CBORDecoder` and calls its `decode()` method.\n 2. The `decode()` method reads the initial byte and dispatches control to a specific handler based on the major type. For an Array (Major Type 4), it calls `decode_array`.\n 3. `decode_array` loops and calls `self.decode()` for each item, leading to deep recursion when parsing a payload like `[...[...[1]...]...]`.\n\n### PoC\n\n```\nimport cbor2\n\nDEPTH = 1000\n\npayload = b'\\x81' * DEPTH + b'\\x01'\nprint(f\"[*] Payload size: {len(payload) / 1024:.2f} KB\")\nprint(\"[*] Triggering decoder...\")\n\ntry:\n cbor2.loads(payload)\n print(\"[+] Parsed successfully (Not Vulnerable)\")\nexcept RecursionError:\n print(\"\\n[!] VULNERABLE: RecursionError triggered!\")\nexcept Exception as e:\n print(f\"\\n[-] Unexpected Error: {type(e).__name__}: {e}\")\n```\n\n### Impact\n\n- Scope: This vulnerability affects any application using `cbor2` to parse untrusted data. Common use cases include IoT data processing, WebAuthn (FIDO2) authentication flows, and inter-service communication over COSE (CBOR Object Signing and Encryption).\n- Attack Vector: A remote, unauthenticated attacker can achieve a full Denial of Service with a highly efficient, low-bandwidth attack. A payload under 100KB is sufficient to reliably terminate a Python worker process.\n\n### Credit\n\nThis issue was discovered by Kevin Tu of TMIR at ByteDance. The patch was developed by @agronholm.", "title": "osv - https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/PyPI%2FGHSA-3c37-wwvx-h642.json?alt=media" }, { "category": "description", "text": "cbor2 provides encoding and decoding for the Concise Binary Object Representation (CBOR) serialization format. Versions prior to 5.9.0 are vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding deeply nested CBOR structures. This vulnerability affects both the pure Python implementation and the C extension `_cbor2`. The C extension relies on Python's internal recursion limits `Py_EnterRecursiveCall` rather than a data-driven depth limit, meaning it still raises `RecursionError` and crashes the worker process when the limit is hit. While the library handles moderate nesting levels, it lacks a hard depth limit. An attacker can supply a crafted CBOR payload containing approximately 100,000 nested arrays `0x81`. When `cbor2.loads()` attempts to parse this, it hits the Python interpreter's maximum recursion depth or exhausts the stack, causing the process to crash with a `RecursionError`. Because the library does not enforce its own limits, it allows an external attacker to exhaust the host application's stack resource. In many web application servers (e.g., Gunicorn, Uvicorn) or task queues (Celery), an unhandled `RecursionError` terminates the worker process immediately. By sending a stream of these small (<100KB) malicious packets, an attacker can repeatedly crash worker processes, resulting in a complete Denial of Service for the application. Version 5.9.0 patches the issue.", "title": "debian - https://security-tracker.debian.org/tracker/CVE-2026-26209" }, { "category": "other", "text": "0.00045", "title": "EPSS" }, { "category": "other", "text": "3.7", "title": "NCSC Score" }, { "category": "other", "text": "There is cwe data available from source Redhat, There is product data available from source Redhat", "title": "NCSC Score top increasing factors" }, { "category": "other", "text": "Is related to (a version of) an uncommon product, There is exploit data available from source Nvd", "title": "NCSC Score top decreasing factors" }, { "category": "details", "text": "Severity: 2\n", "title": "Vendor assessment" } ], "product_status": { "known_affected": [ "CSAFPID-5900044", "CSAFPID-1439279", "CSAFPID-1508257", "CSAFPID-2858641", "CSAFPID-2858642", "CSAFPID-2858643", "CSAFPID-3112098", "CSAFPID-5008756", "CSAFPID-5009266", "CSAFPID-5198605", "CSAFPID-5198606", "CSAFPID-5205180", "CSAFPID-5206383", "CSAFPID-5206384", "CSAFPID-5206387", "CSAFPID-5206388", "CSAFPID-5206389", "CSAFPID-5206390", "CSAFPID-5811320", "CSAFPID-5811347", "CSAFPID-5811351", "CSAFPID-5826732", "CSAFPID-1075813", "CSAFPID-1075814", "CSAFPID-1640791", "CSAFPID-3931679", "CSAFPID-3931680", "CSAFPID-3931681", "CSAFPID-3931682", "CSAFPID-3931683", "CSAFPID-3931684", "CSAFPID-3931685", "CSAFPID-3931686", "CSAFPID-3931687", "CSAFPID-3931688", "CSAFPID-3931689", "CSAFPID-3931690", "CSAFPID-3931691", "CSAFPID-3931693", "CSAFPID-3931694", "CSAFPID-3931695", "CSAFPID-3931696", "CSAFPID-3931697", "CSAFPID-3931698", "CSAFPID-3931699", "CSAFPID-3931700", "CSAFPID-3931701", "CSAFPID-3931702", "CSAFPID-3931703", "CSAFPID-3931704", "CSAFPID-3931705", "CSAFPID-3931706", "CSAFPID-3931707", "CSAFPID-3931708", "CSAFPID-5315933", "CSAFPID-5315934", "CSAFPID-5315935", "CSAFPID-5315936", "CSAFPID-5315937", "CSAFPID-5315938", "CSAFPID-5317854", "CSAFPID-5494080", "CSAFPID-5908032", "CSAFPID-5195300", "CSAFPID-5195301" ] }, "references": [ { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-26209" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/26xxx/CVE-2026-26209.json" }, { "category": "external", "summary": "Source - redhat", "url": "https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-26209.json" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-3c37-wwvx-h642" }, { "category": "external", "summary": "Source - osv", "url": "https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/PyPI%2FGHSA-3c37-wwvx-h642.json?alt=media" }, { "category": "external", "summary": "Source - debian", "url": "https://security-tracker.debian.org/tracker/CVE-2026-26209" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; osv; redhat", "url": "https://github.com/agronholm/cbor2/commit/e61a5f365ba610d5907a0ae1bc72769bba34294b" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; osv; redhat", "url": "https://github.com/agronholm/cbor2/pull/275" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; osv; redhat", "url": "https://github.com/agronholm/cbor2/releases/tag/5.9.0" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; osv; redhat", "url": "https://github.com/agronholm/cbor2/security/advisories/GHSA-3c37-wwvx-h642" }, { "category": "external", "summary": "Reference - redhat", "url": "https://www.cve.org/CVERecord?id=CVE-2026-26209" }, { "category": "external", "summary": "Reference - github; osv; redhat", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26209" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-3c37-wwvx-h642" } ], "scores": [ { "cvss_v3": { "version": "3.0", "vectorString": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "products": [ "CSAFPID-1075813", "CSAFPID-1075814", "CSAFPID-1439279", "CSAFPID-1508257", "CSAFPID-1640791", "CSAFPID-2858641", "CSAFPID-2858642", "CSAFPID-2858643", "CSAFPID-3112098", "CSAFPID-3931679", "CSAFPID-3931680", "CSAFPID-3931681", "CSAFPID-3931682", "CSAFPID-3931683", "CSAFPID-3931684", "CSAFPID-3931685", "CSAFPID-3931686", "CSAFPID-3931687", "CSAFPID-3931688", "CSAFPID-3931689", "CSAFPID-3931690", "CSAFPID-3931691", "CSAFPID-3931693", "CSAFPID-3931694", "CSAFPID-3931695", "CSAFPID-3931696", "CSAFPID-3931697", "CSAFPID-3931698", "CSAFPID-3931699", "CSAFPID-3931700", "CSAFPID-3931701", "CSAFPID-3931702", "CSAFPID-3931703", "CSAFPID-3931704", "CSAFPID-3931705", "CSAFPID-3931706", "CSAFPID-3931707", "CSAFPID-3931708", "CSAFPID-5008756", "CSAFPID-5009266", "CSAFPID-5195300", "CSAFPID-5195301", "CSAFPID-5198605", "CSAFPID-5198606", "CSAFPID-5205180", "CSAFPID-5206383", "CSAFPID-5206384", "CSAFPID-5206387", "CSAFPID-5206388", "CSAFPID-5206389", "CSAFPID-5206390", "CSAFPID-5315933", "CSAFPID-5315934", "CSAFPID-5315935", "CSAFPID-5315936", "CSAFPID-5315937", "CSAFPID-5315938", "CSAFPID-5317854", "CSAFPID-5494080", "CSAFPID-5811320", "CSAFPID-5811347", "CSAFPID-5811351", "CSAFPID-5826732", "CSAFPID-5900044", "CSAFPID-5908032" ] } ], "title": "CVE-2026-26209" } ] }