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CVE-2026-63435

Mail: Email address spoofing via malformed RFC 2047 encoded-words

Published: Sep 1, 2026Updated: Sep 2, 2026 Sources: CVE List NVDCWE-436
5.3MEDIUM
NVD MITRE
EPSS Score
0.3%
Top 74.5%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available
Self-Check
Not available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-436

Affected Products

mikel
mail

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

References

https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859
github.com
https://github.com/mikel/mail/pull/1664
github.com
https://github.com/mikel/mail/releases/tag/2.9.1
github.com
and 1 more references View all →

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