{"id":"CVE-2026-63435","aliases":["GHSA-mvxr-6m87-mv2q"],"url":"https://o3.security/vulnerability/CVE-2026-63435","summary":"Mail: Email address spoofing via malformed RFC 2047 encoded-words","details":"Mail is an internet library for Ruby designed to handle email generation, parsing, and sending. Prior to 2.9.1, Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode used a single String#match and an overly greedy charset capture to decode only the first RFC 2047 encoded-word and mishandle surrounding or subsequent text. A crafted malformed encoded-word in an address display name or local part could cross ? delimiters and make decoded From, To, or Reply-To header values differ from the raw values inspected by a human reviewer or downstream parser, enabling apparent sender or recipient spoofing, phishing, or authorization-check bypass. This issue is fixed in version 2.9.1.","published":"2026-09-01T20:09:20.820Z","modified":"2026-09-04T03:30:48.221353042Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},"epss":{"score":0.00328,"percentile":0.25438,"asOf":"2026-09-03"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"mail","fixedVersion":"2.9.1"}],"fix":{"url":"https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859","label":"mikel/mail@f9d59c2"},"references":[{"type":"WEB","url":"https://github.com/mikel/mail/releases/tag/2.9.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63435.json"},{"type":"ADVISORY","url":"https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63435"},{"type":"FIX","url":"https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859"},{"type":"FIX","url":"https://github.com/mikel/mail/pull/1664"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-04T03:30:48.221353042Z"}}