CVE-2026-39971
Serendipity: Host Header Injection leads to SMTP header injection via unvalidated HTTP_HOST
Description
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.
INFO
Published Date :
April 14, 2026, 11:35 p.m.
Last Modified :
April 14, 2026, 11:35 p.m.
Remotely Exploit :
No
Source :
GitHub_M
Affected Products
The following products are affected by CVE-2026-39971
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update Serendipity to version 2.6.0 or later.
- Apply vendor patches if available.
- Validate all user inputs carefully.
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CVE-2026-39971 vulnerability anywhere in the article.