CVE-2026-39963

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.

CVSS 3.1

6.9CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

EPSS

0.2% chance of exploitation in the next 30 days; higher than 12% of CVEs (scores of 2026-10-26)

CWE

CWE-565

Published

2026-04-15

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Affected

• s9y:serendipity

References

• https://github.com/s9y/Serendipity/releases/tag/2.6.0
• https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf
• https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf

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