CVE-2026-39971
7.2 · HIGHOverview
CVE-2026-39971 is a high-severity vulnerability affecting s9y serendipity. It was published on April 15, 2026 and has a CVSS 3.1 base score of 7.2 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.2, rated HIGH. 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 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.
Remediation
Check the references section for vendor advisories and patches from s9y. Update serendipity to the latest patched version. 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.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| s9y | serendipity | >= 0, < 2.6.0 | Affected |
Frequently Asked Questions
What is CVE-2026-39971?
CVE-2026-39971 is a high-severity vulnerability affecting s9y serendipity. It was published on April 15, 2026 and has a CVSS 3.1 base score of 7.2 (HIGH).
How severe is CVE-2026-39971?
This vulnerability has a CVSS 3.1 base score of 7.2, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2026-39971?
Check the references section for vendor advisories and patches from s9y. Update serendipity to the latest patched version. 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-2026-39971?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-39971 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
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