CVE-2026-63435: 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…

PriorityP428medium5.3CVSS 3.1

AVNACLPRNUINSUCNILAN

EPSS

0.33%

25.7th percentile

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.

Affected

2 ranges

Vendor	Product	Version range	Fixed in
mikel	mail	< 2.9.1	2.9.1
nextcloud	mail	>= 0 < 2.9.1	2.9.1

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