CVE Tools
Sign in

CVE-2026-39963

Serendipity: Host Header Injection enables authentication cookie scoping to an attacker-controlled domain

Published: Apr 14, 2026Updated: Apr 23, 2026 Sources: CVE List NVDCWE-565
NVD MITRE
6.9CVSSMEDIUM
EPSS Score
0.2%
Top 87.2%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:HPR:NUI:RS:CC:HI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:RUser Interaction
Required
Scope
S:CScope
Changed
Impact
C:HConfidentiality
High
I:LIntegrity
Low
A:NAvailability
None
Open in CVSS calculator →

Weaknesses

CWE-565

Affected Products

serendipitys9y
On-premWeb App
Web & CMS Plugins / cms-core
Serendipitys9y
On-premWeb App
Web & CMS Plugins / cms-core
s9yoss-projectWeb & CMS Pluginsaka serendipity event freetag

Exploitability

Official Patch Available

References

https://github.com/s9y/Serendipity/releases/tag/2.6.0
github.com
https://github.com/s9y/Serendipity/security/advisories/GHSA-4m6c-649p-f6gf
github.com

Timeline

Published
Apr 14, 2026
Last Updated
Apr 23, 2026

Unlock Complete Vulnerability Intelligence

Get the full picture for CVE-2026-39963 and every CVE in our database. Create a free account — no credit card required.

Create Free Account
Plain-language analysis
Impact assessment and exploitation scenario in plain English
Attack graph visualization
Interactive attack path and kill chain mapping
Exploit details & PoC links
ExploitDB, Metasploit, GitHub PoCs with direct links
Nuclei scanner templates
Ready-to-use vulnerability scanner templates
Full remediation guide
Patch instructions, workarounds, and compliance impact
Interactive AI chat
Ask questions about this vulnerability in natural language
Related vulnerabilities
Semantically similar CVEs and attack patterns
REST API & MCP access
Integrate vulnerability data into your workflows