What is CVE-2026-39971?

CVE-2026-39971 is a high-severity vulnerability in S9y Serendipity, classified under HTTP Response Splitting. CVSS score: 7.2/10. Published 2026-04-14.

How severe is CVE-2026-39971?

High severity. CVSS v3 base score is 7.2 out of 10.

Vulnerability in S9y Serendipity

CVE-2026-39971

Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the email sending functionality in include/functions.inc.php inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without validation, and the ex…

EPSS: 0.001 (20.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.

Affected products

S9y Serendipity — versions < 2.6.0

Weakness classification (CWE)

CWE-113 — HTTP Response Splitting

References

https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r (x_refsource_CONFIRM)
https://github.com/s9y/Serendipity/releases/tag/2.6.0 (x_refsource_MISC)

Frequently asked questions

What is CVE-2026-39971?: CVE-2026-39971 is a high-severity vulnerability in S9y Serendipity, classified under HTTP Response Splitting. CVSS score: 7.2/10. Published 2026-04-14.
How severe is CVE-2026-39971?: High severity. CVSS v3 base score is 7.2 out of 10.