Vulnerability Description
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.
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859
- https://github.com/mikel/mail/pull/1664
- https://github.com/mikel/mail/releases/tag/2.9.1
- https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q
FAQ
What is CVE-2026-63435?
CVE-2026-63435 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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#m...
How severe is CVE-2026-63435?
CVE-2026-63435 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-63435?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.