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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63435
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-01 21:18:35 UTC
Updated2026-09-09 21:09:13 UTC
DescriptionMail 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS: 0.003280000 probability, percentile 0.256960000 (date 2026-09-10)

Problem Types: CWE-436 | CWE-436 CWE-436: Interpretation Conflict

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mikel Mail affected < 2.9.1 Not specified

References

ReferenceSourceLinkTags
github.com/mikel/mail/releases/tag/2.9.1 [email protected] github.com
github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q [email protected] github.com
github.com/mikel/mail/pull/1664 [email protected] github.com
github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859 [email protected] github.com
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