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CVE-2026-39971

CVE-2026-39971 · Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 7.2 · High · EPSS 0.3% · Fix available

Published
Updated

Stack: php

Affected products and versions

  • serendipity

    Versions
    • < 2.6.0: Affected

    No fix published

  • s9y/serendipity Packagist

    Versions
    • 2.0.0
    • 2.0.1
    • 2.0.2
    • 2.0.3
    • 2.0.4
    • 2.0.5
    • 2.1-beta1
    • 2.1-beta2
    • 2.1-beta3
    • 2.1-rc1
    • 2.1.0
    • 2.1.1
    • 2.1.2
    • 2.1.3
    • 2.1.4
    • 2.1.5
    • 2.1.6
    • 2.2.1-alpha1
    • 2.3-beta1
    • 2.3-rc1
    • 2.3.0
    • 2.3.1
    • 2.3.2
    • 2.3.3
    • 2.3.4
    • 2.3.5
    • 2.4-beta1
    • 2.4.0
    • 2.5-beta1
    • 2.5.0
    • 2.6-beta1
    Affected ranges
    • ECOSYSTEM: < 2.6.0

    Update to 2.6.0

Original sources

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