cvedb.io
CVE-2026-39971
HIGH · CVSS 7.2
EPSS exploitation probability: 0%
Published 2026-04-15T04:17:39.763 · Last modified 2026-06-17T10:42:50.143

Summary

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.

Affected products

s9y — serendipity

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References

This product uses data from the NVD API but is not endorsed or certified by the NVD. Informational only; not professional security advice.