CVE-2026-39963: Serendipity has a Host Header Injection allows authentication cookie scoping to attacker-controlled domain in functions_config.inc.php

April 14, 2026 (updated April 15, 2026)

The serendipity_setCookie() function uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker can force authentication cookies — including session tokens and auto-login tokens — to be scoped to an attacker-controlled domain, facilitating session hijacking.

References

github.com/advisories/GHSA-4m6c-649p-f6gf
github.com/s9y/Serendipity/releases/tag/2.6.0
github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf
nvd.nist.gov/vuln/detail/CVE-2026-39963

Code Behaviors & Features

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