{
    "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-2026-34831",
        "tracking": {
            "current_release_date": "2026-04-03T15:35:49.032451Z",
            "generator": {
                "date": "2026-02-17T15:00:00Z",
                "engine": {
                    "name": "V.E.L.M.A",
                    "version": "1.7"
                }
            },
            "id": "CVE-2026-34831",
            "initial_release_date": "2026-04-02T17:28:54.429569Z",
            "revision_history": [
                {
                    "date": "2026-04-02T17:28:54.429569Z",
                    "number": "1",
                    "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (1).| CWES updated (1)."
                },
                {
                    "date": "2026-04-02T17:28:56.774822Z",
                    "number": "2",
                    "summary": "NCSC Score created."
                },
                {
                    "date": "2026-04-02T17:38:50.617317Z",
                    "number": "3",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (3).| References created (1).| CWES updated (1)."
                },
                {
                    "date": "2026-04-02T17:38:54.957025Z",
                    "number": "4",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-04-02T20:52:57.081609Z",
                    "number": "5",
                    "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)."
                },
                {
                    "date": "2026-04-03T00:44:11.333185Z",
                    "number": "6",
                    "summary": "Source created.| CVE status created. (valid)| Products connected (2)."
                },
                {
                    "date": "2026-04-03T00:44:16.705828Z",
                    "number": "7",
                    "summary": "NCSC Score updated."
                },
                {
                    "date": "2026-04-03T06:45:55.517677Z",
                    "number": "8",
                    "summary": "Description created for source."
                },
                {
                    "date": "2026-04-03T15:30:48.062916Z",
                    "number": "9",
                    "summary": "Source connected.| CVE status created. (valid)| EPSS created."
                },
                {
                    "date": "2026-04-03T15:30:52.548329Z",
                    "number": "10",
                    "summary": "NCSC Score updated."
                }
            ],
            "status": "interim",
            "version": "10"
        }
    },
    "product_tree": {
        "branches": [
            {
                "branches": [
                    {
                        "branches": [
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/<2.2.23",
                                "product": {
                                    "name": "vers:unknown/<2.2.23",
                                    "product_id": "CSAFPID-5985093"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=3.0.0.beta1|<3.1.21",
                                "product": {
                                    "name": "vers:unknown/>=3.0.0.beta1|<3.1.21",
                                    "product_id": "CSAFPID-5985094"
                                }
                            },
                            {
                                "category": "product_version_range",
                                "name": "vers:unknown/>=3.2.0|<3.2.6",
                                "product": {
                                    "name": "vers:unknown/>=3.2.0|<3.2.6",
                                    "product_id": "CSAFPID-5985095"
                                }
                            }
                        ],
                        "category": "product_name",
                        "name": "rack"
                    }
                ],
                "category": "vendor",
                "name": "rack"
            },
            {
                "branches": [
                    {
                        "branches": [
                            {
                                "branches": [
                                    {
                                        "category": "product_version_range",
                                        "name": "vers:deb/unknown",
                                        "product": {
                                            "name": "vers:deb/unknown",
                                            "product_id": "CSAFPID-2065710"
                                        }
                                    }
                                ],
                                "category": "product_name",
                                "name": "ruby-rack"
                            }
                        ],
                        "category": "product_family",
                        "name": "bookworm"
                    },
                    {
                        "branches": [
                            {
                                "branches": [
                                    {
                                        "category": "product_version_range",
                                        "name": "vers:deb/unknown",
                                        "product": {
                                            "name": "vers:deb/unknown",
                                            "product_id": "CSAFPID-2065711"
                                        }
                                    }
                                ],
                                "category": "product_name",
                                "name": "ruby-rack"
                            }
                        ],
                        "category": "product_family",
                        "name": "bullseye"
                    }
                ],
                "category": "vendor",
                "name": "Debian"
            }
        ]
    },
    "vulnerabilities": [
        {
            "cve": "CVE-2026-34831",
            "cwe": {
                "id": "CWE-130",
                "name": "Improper Handling of Length Parameter Inconsistency"
            },
            "notes": [
                {
                    "category": "description",
                    "text": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
                    "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-34831"
                },
                {
                    "category": "description",
                    "text": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
                    "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/34xxx/CVE-2026-34831.json"
                },
                {
                    "category": "description",
                    "text": "## Summary\n\n`Rack::Files#fail` sets the `Content-Length` response header using `String#size` instead of `String#bytesize`. When the response body contains multibyte UTF-8 characters, the declared `Content-Length` is smaller than the number of bytes actually sent on the wire.\n\nBecause `Rack::Files` reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters.\n\nThis results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect `Content-Length` value.\n\n## Details\n\n`Rack::Files#fail` constructs error responses using logic equivalent to:\n\n```ruby\ndef fail(status, body, headers = {})\n  body += \"\\n\"\n  [\n    status,\n    {\n      \"content-type\" => \"text/plain\",\n      \"content-length\" => body.size.to_s,\n      \"x-cascade\" => \"pass\"\n    }.merge!(headers),\n    [body]\n  ]\nend\n```\n\nHere, `body.size` returns the number of characters, not the number of bytes. For multibyte UTF-8 strings, this produces an incorrect `Content-Length` value.\n\n`Rack::Files` includes the decoded request path in 404 responses. A request containing percent-encoded UTF-8 path components therefore causes the response body to contain multibyte characters, while the `Content-Length` header still reflects character count rather than byte count.\n\nAs a result, the server can send more bytes than declared in the response headers.\n\nThis violates HTTP message framing requirements, which define `Content-Length` as the number of octets in the message body.\n\n## Impact\n\nApplications using `Rack::Files` may emit incorrectly framed error responses when handling requests for non-existent paths containing multibyte characters.\n\nIn some deployment topologies, particularly with keep-alive connections and intermediaries that rely on `Content-Length`, this mismatch may lead to response parsing inconsistencies or response desynchronization. The practical exploitability depends on the behavior of downstream proxies, clients, and connection reuse.\n\nEven where no secondary exploitation is possible, the response is malformed and may trigger protocol errors in strict components.\n\n## Mitigation\n\n* Update to a patched version of Rack that computes `Content-Length` using `String#bytesize`.\n* Avoid exposing `Rack::Files` directly to untrusted traffic until a fix is available, if operationally feasible.\n* Where possible, place Rack behind a proxy or server that normalizes or rejects malformed backend responses.\n* Prefer closing backend connections on error paths if response framing anomalies are a concern.",
                    "title": "github - https://api.github.com/advisories/GHSA-q2ww-5357-x388"
                },
                {
                    "category": "description",
                    "text": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.",
                    "title": "debian - https://security-tracker.debian.org/tracker/CVE-2026-34831"
                },
                {
                    "category": "other",
                    "text": "0.00028",
                    "title": "EPSS"
                },
                {
                    "category": "other",
                    "text": "3.9",
                    "title": "NCSC Score"
                },
                {
                    "category": "other",
                    "text": "The value of the most recent EPSS score, Is related to (a version of) an uncommon product, There is cwe data available from source Nvd",
                    "title": "NCSC Score top decreasing factors"
                }
            ],
            "product_status": {
                "known_affected": [
                    "CSAFPID-5985093",
                    "CSAFPID-5985094",
                    "CSAFPID-5985095",
                    "CSAFPID-2065710",
                    "CSAFPID-2065711"
                ]
            },
            "references": [
                {
                    "category": "external",
                    "summary": "Source - nvd",
                    "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-34831"
                },
                {
                    "category": "external",
                    "summary": "Source - cveprojectv5",
                    "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/34xxx/CVE-2026-34831.json"
                },
                {
                    "category": "external",
                    "summary": "Source - github",
                    "url": "https://api.github.com/advisories/GHSA-q2ww-5357-x388"
                },
                {
                    "category": "external",
                    "summary": "Source - debian",
                    "url": "https://security-tracker.debian.org/tracker/CVE-2026-34831"
                },
                {
                    "category": "external",
                    "summary": "Source - first",
                    "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0"
                },
                {
                    "category": "external",
                    "summary": "Reference - cveprojectv5; github; nvd",
                    "url": "https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388"
                },
                {
                    "category": "external",
                    "summary": "Reference - github",
                    "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34831"
                },
                {
                    "category": "external",
                    "summary": "Reference - github",
                    "url": "https://github.com/advisories/GHSA-q2ww-5357-x388"
                }
            ],
            "scores": [
                {
                    "cvss_v3": {
                        "version": "3.1",
                        "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
                        "baseScore": 4.8,
                        "baseSeverity": "MEDIUM"
                    },
                    "products": [
                        "CSAFPID-2065710",
                        "CSAFPID-2065711",
                        "CSAFPID-5985093",
                        "CSAFPID-5985094",
                        "CSAFPID-5985095"
                    ]
                }
            ],
            "title": "CVE-2026-34831"
        }
    ]
}