{"api_version":"1","generated_at":"2026-04-09T23:55:41+00:00","cve":"CVE-2026-34831","urls":{"html":"https://cve.report/CVE-2026-34831","api":"https://cve.report/api/cve/CVE-2026-34831.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-34831","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-34831"},"summary":{"title":"Rack: Content-Length mismatch in Rack::Files error responses","description":"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. 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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."}],"metrics":[{"cvssV3_1":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":4.8,"baseSeverity":"MEDIUM","confidentialityImpact":"LOW","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-130","description":"CWE-130: Improper Handling of Length Parameter Inconsistency","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-135","description":"CWE-135: Incorrect Calculation of Multi-Byte String Length","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-04-02T16:43:08.762Z","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M"},"references":[{"name":"https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388","tags":["x_refsource_CONFIRM"],"url":"https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388"}],"source":{"advisory":"GHSA-q2ww-5357-x388","discovery":"UNKNOWN"},"title":"Rack: Content-Length mismatch in Rack::Files error responses"}},"cveMetadata":{"assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","assignerShortName":"GitHub_M","cveId":"CVE-2026-34831","datePublished":"2026-04-02T16:43:08.762Z","dateReserved":"2026-03-30T20:52:53.284Z","dateUpdated":"2026-04-02T16:43:08.762Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-04-02 17:16:26","lastModifiedDate":"2026-04-03 16:10:23","problem_types":["CWE-130","CWE-135","CWE-130 CWE-130: Improper Handling of Length Parameter Inconsistency","CWE-135 CWE-135: Incorrect Calculation of Multi-Byte String Length"],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"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","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":2.2,"impactScore":2.5}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"34831","Ordinal":"1","Title":"Rack: Content-Length mismatch in Rack::Files error responses","CVE":"CVE-2026-34831","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"34831","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Rack: Content-Length mismatch in Rack::Files error responses"}]}}}