s9y Serendipity up to 2.5.x functions_config.inc.php serendipity_setCookie HTTP_HOST cookie validation

Summaryinfo

A vulnerability has been found in s9y Serendipity up to 2.5.x and classified as problematic. The affected element is the function serendipity_setCookie of the file include/functions_config.inc.php. The manipulation of the argument HTTP_HOST leads to cookie validation. This vulnerability is referenced as CVE-2026-39963. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in s9y Serendipity up to 2.5.x. It has been rated as problematic. This issue affects the function serendipity_setCookie of the file include/functions_config.inc.php. The manipulation of the argument HTTP_HOST with an unknown input leads to a cookie validation vulnerability. Using CWE to declare the problem leads to CWE-565. The product relies on the existence or values of cookies when performing security-critical operations, but it does not properly ensure that the setting is valid for the associated user. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-39963 since 04/08/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available.

By approaching the search of inurl:include/functions_config.inc.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 2.6.0 eliminates this vulnerability.

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

• Content Management System

Vendor

• s9y

Name

• Serendipity

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5

License

• free

Website

• Product: https://github.com/s9y/Serendipity/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Discussion