CVE-2026-39963
Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain
Description
Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0.
INFO
Published Date :
April 15, 2026, 4:17 a.m.
Last Modified :
April 23, 2026, 1:58 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update Serendipity to version 2.6.0 or later.
- Validate Host header inputs.
- Ensure secure cookie configurations.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-39963.
| URL | Resource |
|---|---|
| https://github.com/s9y/Serendipity/releases/tag/2.6.0 | Product |
| https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf | Exploit Vendor Advisory Mitigation |
| https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf | Exploit Vendor Advisory Mitigation |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-39963 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-39963
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-39963 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-39963 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 23, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:s9y:serendipity:*:*:*:*:*:*:*:* versions up to (excluding) 2.6.0 *cpe:2.3:a:s9y:serendipity:2.6.0:beta1:*:*:*:*:*:* Added Reference Type GitHub, Inc.: https://github.com/s9y/Serendipity/releases/tag/2.6.0 Types: Product Added Reference Type CISA-ADP: https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf Types: Exploit, Mitigation, Vendor Advisory Added Reference Type GitHub, Inc.: https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf Types: Exploit, Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 15, 2026
Action Type Old Value New Value Added Reference https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf -
New CVE Received by [email protected]
Apr. 15, 2026
Action Type Old Value New Value Added Description Serendipity is a PHP-powered weblog engine. In versions 2.6-beta2 and below, the serendipity_setCookie() function in include/functions_config.inc.php uses $_SERVER['HTTP_HOST'] without validation as the domain parameter of setcookie(). An attacker who can influence the Host header at login time, such as via MITM, reverse proxy misconfiguration, or load balancer manipulation, can force authentication cookies including session tokens and auto-login tokens to be scoped to an attacker-controlled domain. This enables session fixation, token leakage to attacker-controlled infrastructure, and privilege escalation if an admin logs in under a poisoned Host header. This issue has been fixed in version 2.6.0. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N Added CWE CWE-565 Added Reference https://github.com/s9y/Serendipity/releases/tag/2.6.0 Added Reference https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf