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CVE-2026-63435

5.3 · MEDIUM

Mail is an internet library for Ruby designed to handle email generation, parsing, and sending.

Published Sep 1, 2026CWE-436EPSS 0.45%

Overview

CVE-2026-63435 is a medium-severity vulnerability. It was published on September 1, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859GitHubgithub.com/mikel/mail/pull/1664GitHubgithub.com/mikel/mail/releases/tag/2.9.1GitHubgithub.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q

How CyberStrike helps

Frequently asked questions

What is CVE-2026-63435?

CVE-2026-63435 is a medium-severity vulnerability. It was published on September 1, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-63435?

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-63435?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-63435?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-63435 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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