{"id":"CVE-2026-34831","summary":"Rack: Content-Length mismatch in Rack::Files error responses","details":"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.","aliases":["GHSA-q2ww-5357-x388"],"modified":"2026-04-13T04:29:46.857576Z","published":"2026-04-02T16:43:08.762Z","related":["CGA-whh4-hgx9-244x","openSUSE-SU-2026:10508-1"],"database_specific":{"cna_assigner":"GitHub_M","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34831.json","cwe_ids":["CWE-130","CWE-135"]},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34831.json"},{"type":"ADVISORY","url":"https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34831"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/rack/rack","events":[{"introduced":"0"},{"fixed":"f2af0c8f869193fa7bb7d20b619b3003418e1055"},{"introduced":"572a42a705b423ce98ef4e81435d4f60fb0ae53d"},{"fixed":"ae8431120e66e92d1885ab8ec0a553d9cad5ec13"},{"introduced":"b68251c03788ff39d4a4b25424df7360426e4afd"},{"fixed":"e1f22fdbe99afd2126b6fbf05bb12399359574b7"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"2.2.23"},{"introduced":"3.0.0.beta1"},{"fixed":"3.1.21"},{"introduced":"3.2.0"},{"fixed":"3.2.6"}],"source":"AFFECTED_FIELD"}}],"versions":["0.1","0.2","0.3","1.0","1.3.0","1.3.0.beta","1.3.0.beta2","1.4.0","1.4.1","1.5.0","1.5.1","1.6.0.beta","2.0.0","2.0.0.alpha","2.0.0.rc1","2.0.1","2.1.0","2.2.0","2.2.3","2.2.4","3.0.0","3.0.0.beta1","3.0.0.rc1","v2.2.1","v2.2.10","v2.2.11","v2.2.12","v2.2.13","v2.2.14","v2.2.15","v2.2.16","v2.2.17","v2.2.18","v2.2.19","v2.2.2","v2.2.20","v2.2.21","v2.2.22","v2.2.5","v2.2.6","v2.2.6.1","v2.2.6.2","v2.2.7","v2.2.8","v2.2.9","v3.1.0","v3.1.10","v3.1.11","v3.1.12","v3.1.13","v3.1.14","v3.1.15","v3.1.16","v3.1.17","v3.1.18","v3.1.19","v3.1.2","v3.1.20","v3.1.3","v3.1.4","v3.1.5","v3.1.6","v3.1.7","v3.1.8","v3.1.9","v3.2.0","v3.2.1","v3.2.2","v3.2.3","v3.2.4","v3.2.5"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-34831.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"}]}