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CVE-2026-39971
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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