CVE-2026-39971: Serendipity is a PHP-powered weblog engine

Q: How do I fix CVE-2026-39971?

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

Q: Is CVE-2026-39971 being exploited?

CVE-2026-39971 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-2026-39971 affect?

CVE-2026-39971 affects serendipity. Severity is high (CVSS 7.2). 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 exi

Q: How urgent is CVE-2026-39971?

Priority 39/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.2REMOTEUPGRADE

CVE-2026-39971 is a high-severity flaw (CVSS 7.2) 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 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 notificati

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 83%)
CISA exploited list	No
Weakness	CWE-113
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-2026-39971?

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

Is CVE-2026-39971 being exploited?

CVE-2026-39971 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-2026-39971 affect?

CVE-2026-39971 affects serendipity. Severity is high (CVSS 7.2). 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 exi

How urgent is CVE-2026-39971?

Priority 39/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

Related CVEs

CVE-2026-39963 MEDIUM 6.9 UPGRADE Serendipity is a PHP-powered weblog engine

References

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