Is CVE-2026-39971 actively exploited?

No active exploitation of CVE-2026-39971 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-39971 be exploited remotely?

Yes. CVE-2026-39971 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-39971?

CVE-2026-39971 has a CVSS score of 7.2 (HIGH).

HOME VULNERABILITIESCVE-2026-39971

HIGH

CVE-2026-39971

CWE-113Published: April 15, 2026· Updated: Apr 17, 2026

7.2

CVSS v3.1

EPSS:0.03%probability of exploitation in 30 daysPercentile:8.1th

Official Description

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 existing sanitization function serendipity_isResponseClean() is not called on HTTP_HOST before embedding it. An attacker who can control the Host header during an email-triggering action such as comment notifications or subscription emails can inject arbitrary SMTP headers into outgoing emails. This enables identity spoofing, reply hijacking via manipulated Message-ID threading, and email reputation abuse through the attacker's domain being embedded in legitimate mail headers. This issue has been fixed in version 2.6.0.

NVD Source

Technical Analysis

CVE-2026-39971 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

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.