CVE-2026-39971

7.2 HIGH 0.3% exploit odds Fix listed Other Web app

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. Limited direct impact.
Exploit odds: 0.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-04-15 04:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-26 22:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.3% in the next 30 days (EPSS).
Severity: 7.2 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-04-15 04:17 UTC
Last modified: 2026-10-26 22:10 UTC
Exploit probability: 0.3% · EPSS, next 30 days
Weakness: CWE-113
Record status: Analyzed

Affected

s9y Serendipity < 2.6.0
s9y Serendipity 2.6.0

Attack profile CVSS 3.1 · 7.2

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-39971.md and follow it. Check whether this project is affected by CVE-2026-39971. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record