Dashboard / CVE-2026-39971

CVE-2026-39971

HIGH
MEDIUM Priority: 0.02 BB Relevance: 74/100
Published: 2026-04-15 Modified: 2026-10-26 First seen: 2026-10-29 Status: active

Attack Surface

Network Low Complexity No Auth No Interaction Scope Change

CVSS Vector Breakdown

AV: Network
AC: Low
PR: None
UI: None
S: Changed
C: Low
I: Low
A: None

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.

Weakness Classification (1)

Affected Software (2)

VendorProductVersion
s9y serendipity < 2.6.0
s9y serendipity 2.6.0

References & Advisories (2)

Bug Bounty Relevance

74 / 100
✓ Network accessible
✓ No authentication
✓ Low complexity
✓ No user interaction

CVSS Score

7.2 / 10.0 v3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

EPSS — Exploitation Probability

0.26%
Raw Score 0.002550
Percentile 17.1%
Date 2026-10-29

EPSS Trend

2026-10-29
0.00255
2026-10-28
0.00255

Intelligence Sources

nvd ref →

External Links