CVE-2026-39963: Serendipity is a PHP-powered weblog engine

Q: How do I fix CVE-2026-39963?

serendipity: upgrade to 2.6.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-39963 being exploited?

CVE-2026-39963 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-39963 affect?

CVE-2026-39963 affects serendipity. Severity is medium (CVSS 6.9). 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

Q: How urgent is CVE-2026-39963?

Priority 32/100. Public exploit reference

Routine

MEDIUM 6.9UPGRADE

CVE-2026-39963 is a medium-severity flaw (CVSS 6.9) affecting serendipity. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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-logi

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-565
Published	2026-04-15
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: s9y

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-15 04:17 UTCPublished CVE record published
2026-10-26 22:10 UTCUpdated Record last modified

s9y serendipity UPGRADE

Affected: < 2.6.0 · 2.6.0 beta1

Fixed in: 2.6.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy serendipity || rpm -q serendipity || serendipity --version

2. UPGRADE to 2.6.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade serendipity

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade serendipity

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-39963?

serendipity: upgrade to 2.6.0. Exact commands for each OS are on this page.

Is CVE-2026-39963 being exploited?

CVE-2026-39963 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-39963 affect?

CVE-2026-39963 affects serendipity. Severity is medium (CVSS 6.9). 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

How urgent is CVE-2026-39963?

Priority 32/100. Public exploit reference

Software pages

PHP vulnerabilities

Related CVEs

CVE-2026-39971 HIGH 7.2 UPGRADE Serendipity is a PHP-powered weblog engine

References

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