{"id":"CVE-2026-34827","aliases":["GHSA-v6x5-cg8r-vv6x"],"url":"https://o3.security/vulnerability/CVE-2026-34827","summary":"Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser","details":"Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as Content-Disposition: form-data; name=\"...\" using repeated String#index searches combined with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing. An unauthenticated attacker can send a crafted multipart/form-data request containing many parts with long backslash-escaped parameter values to trigger excessive CPU usage during multipart parsing. This results in a denial of service condition in Rack applications that accept multipart form data. This issue has been patched in versions 3.1.21 and 3.2.6.","published":"2026-04-02T17:07:48.279Z","modified":"2026-07-27T03:56:44.912445996Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"rack","fixedVersion":"3.1.21"},{"ecosystem":"RubyGems","name":"rack","fixedVersion":"3.2.6"}],"fix":null,"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34827.json"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-34827"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34827.json"},{"type":"ADVISORY","url":"https://github.com/rack/rack/security/advisories/GHSA-v6x5-cg8r-vv6x"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34827"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2454501"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-27T03:56:44.912445996Z"}}