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CVE-2026-39963

6.9 · MEDIUM

Serendipity is a PHP-powered weblog engine.

Published Apr 15, 2026CWE-565EPSS 0.30%

Overview

CVE-2026-39963 is a medium-severity vulnerability. It was published on April 15, 2026 and has a CVSS 3.1 base score of 6.9 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/s9y/Serendipity/releases/tag/2.6.0GitHubgithub.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gfGitHubgithub.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf

How CyberStrike helps

Frequently asked questions

What is CVE-2026-39963?

CVE-2026-39963 is a medium-severity vulnerability. It was published on April 15, 2026 and has a CVSS 3.1 base score of 6.9 (MEDIUM).

How severe is CVE-2026-39963?

This vulnerability has a CVSS 3.1 base score of 6.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-39963?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-39963?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-39963 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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