CVE-2026-39971

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.

CVSS v3 7.2 HIGH

7.2^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/s9y/Serendipity/releases/tag/2.6.0	Patch
https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r	Exploit Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:s9y:serendipity::::::::
	cpe:2.3:a:s9y:serendipity:2.6.0:beta1::::::

History

No history.

Information

Published : 2026-04-15 04:17

Updated : 2026-06-17 10:42

NVD link : CVE-2026-39971

Mitre link : CVE-2026-39971

CVE.ORG link : CVE-2026-39971

JSON object : View

Products Affected

s9y

serendipity

CWE

CWE-113

Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

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