Is CVE-2026-39963 actively exploited?

No active exploitation of CVE-2026-39963 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-39963 be exploited remotely?

Yes. CVE-2026-39963 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-39963?

CVE-2026-39963 has a CVSS score of 6.9 (MEDIUM).

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MEDIUM

CVE-2026-39963

CWE-565Published: April 15, 2026· Updated: Apr 17, 2026

6.9

CVSS v3.1

EPSS:0.04%probability of exploitation in 30 daysPercentile:13.0th

Official 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.

NVD Source

Technical Analysis

CVE-2026-39963 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation does not require any privileges, though user interaction (Required) is needed, which slightly reduces the risk of mass automated attacks.

A successful exploit results in complete confidentiality breach (data exposure), with a CVSS base score of 6.9.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.