What is CVE-2026-39963?

CVE-2026-39963 is a medium-severity vulnerability in S9y Serendipity, classified under Reliance on Cookies without Validation and Integrity Checking. CVSS score: 6.9/10. Published 2026-04-14.

How severe is CVE-2026-39963?

Medium severity. CVSS v3 base score is 6.9 out of 10.

Vulnerability in S9y Serendipity

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…

EPSS: 0.001 (22.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N.

Affected products

S9y Serendipity — versions < 2.6.0

Weakness classification (CWE)

CWE-565 — Reliance on Cookies without Validation and Integrity Checking

References

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

Frequently asked questions

What is CVE-2026-39963?: CVE-2026-39963 is a medium-severity vulnerability in S9y Serendipity, classified under Reliance on Cookies without Validation and Integrity Checking. CVSS score: 6.9/10. Published 2026-04-14.
How severe is CVE-2026-39963?: Medium severity. CVSS v3 base score is 6.9 out of 10.