Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/s9y/Serendipity/releases/tag/2.6.0 Patch
- https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r Exploit, Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 7.2 · s9yNVD modified 2026-10-26 22:10
Affected (CPE criteria) 2
cpe:2.3:a:s9y:serendipity:*:*:*:*:*:*:*:*cpe:2.3:a:s9y:serendipity:2.6.0:beta1:*:*:*:*:*:*
References 2
- https://github.com/s9y/Serendipity/releases/tag/2.6.0 Patch
- https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r Exploit, Mitigation, Vendor Advisory