CVE-2026-63435 (GCVE-0-2026-63435)
Vulnerability from cvelistv5 – Published: 2026-09-01 20:09 – Updated: 2026-09-02 15:44
VLAI
EPSS
VEX
Title
Mail: Email address spoofing via malformed RFC 2047 encoded-words
Summary
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.
Severity
5.3 (Medium)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-02 15:44 UTC
CWE
- CWE-436 - Interpretation Conflict
Assigner
GitHub_M
CNA
References
4 references
| URL | Tags |
|---|---|
| https://github.com/mikel/mail/security/advisories… | x_refsource_CONFIRM |
| https://github.com/mikel/mail/pull/1664 | x_refsource_MISC |
| https://github.com/mikel/mail/commit/f9d59c2e447a… | x_refsource_MISC |
| https://github.com/mikel/mail/releases/tag/2.9.1 | x_refsource_MISC |
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Nomenclature
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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