CVE-2026-63435: Mikel Mail

Medium severity, CVSS 5.3. EPSS: 0.4% chance of exploitation in the next 30 days.

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 products

• Mikel Mail: before 2.9.1 (fixed in 2.9.1)

Published 2026-09-01. Last modified 2026-09-09.