Bug 2527048 (CVE-2026-63435)

Summary: CVE-2026-63435 mail: Mail: Email address spoofing via malformed RFC 2047 encoded-words
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akostadi, amasferr, dmayorov, eshamard, jlledo, jvasik, kaycoth, pantinor, rblanco, tsedmik
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Mail, an internet library for Ruby. The library's decoding of RFC 2047 encoded-words in email headers was vulnerable to an overly greedy charset capture. A remote attacker could exploit this by crafting a malformed encoded-word in an address display name or local part. This could cause the decoded email headers to differ from their original values, leading to sender or recipient spoofing, phishing, or authorization-check bypass.
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Description OSIDB Bzimport 2026-09-01 20:21:15 UTC 
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.