Vulnerability · Published Sep 1, 2026 · Assigned by GitHub_M
CVE-2026-63435Mail: Email address spoofing via malformed RFC 2047 encoded-words
Medium 5.3
In plain English
A medium-severity security flaw in mail from mikel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-mail | no fix listed | DEBIAN-CVE-2026-63435 |
| Debian:13 | ruby-mail | no fix listed | DEBIAN-CVE-2026-63435 |
| Debian:14 | ruby-mail | 2.9.1-1 | DEBIAN-CVE-2026-63435 |
| RubyGems | 2.9.1 | GHSA-mvxr-6m87-mv2q | |
| Ubuntu:24.04:LTS | jruby | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:26.04:LTS | jruby | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:26.10 | jruby | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:22.04:LTS | ruby3.0 | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:24.04:LTS | ruby3.2 | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:26.04:LTS | ruby3.3 | no fix listed | UBUNTU-CVE-2026-63435 |
| Ubuntu:26.10 | ruby3.3 | no fix listed | UBUNTU-CVE-2026-63435 |
Affected products (as reported)
Weakness: CWE-436 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
References
- https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q x_refsource_CONFIRM
- https://github.com/mikel/mail/pull/1664 x_refsource_MISC
- https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859 x_refsource_MISC
- https://github.com/mikel/mail/releases/tag/2.9.1 x_refsource_MISC