TI-2026-45211 Aliases CVE-2026-63435 GHSA-mvxr-6m87-mv2q

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

LOW 30CWE-436Published 2026-09-01 · Updated 2026-09-02

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: None · Low · None
Fix status: Partial Red Hat: 1 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00448 39th percentileScored 2026-11-07

Fix Partial mail (mikel): 2.9.1mail (RubyGems): 2.9.1Red Hat: 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
mikel	mail	before 2.9.1	2.9.1	Patch available	CNA
—	mail (RubyGems)	before 2.9.1	2.9.1	Patch available	GHSA-mvxr-6m87-mv2q

mail Vendormikel Affected before 2.9.1 Fixed in 2.9.1 Patch available CNA
mail (RubyGems) Vendor— Affected before 2.9.1 Fixed in 2.9.1 Patch available GHSA-mvxr-6m87-mv2q

Remediation

Fix · CNA mail (mikel) Fixed in 2.9.1
Fix · GHSA-mvxr-6m87-mv2q mail (RubyGems) Fixed in 2.9.1 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat 3scale API Management Platform 2	Affected	No fix yet: Fix deferred

Timeline

2026-10-02 Threatist record created from CVE-2026-63435
2026-10-03 Alias added: GHSA-mvxr-6m87-mv2q

References

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-63435

Other 5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences