CVE-2026-39963
Description
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.
How to fix
- s9y serendipity2.6.0 or later
- s9y/serendipity2.6.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| s9y serendipity | v < 2.6.0, 2.6.0 | 2.6.0 |
| s9y/serendipityPackagist | v < 2.6.0 | 2.6.0 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.