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VulnerabilityPublished

CVE-2026-39963: s9y Serendipity · Unvalidated Cookie Trust

Affects s9y SerendipitySource CVE Database V5

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Not known to be exploited · CVSS 6.9 Medium : upgrade to 2.6.0 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
6.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.6.0
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 14 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade Serendipity and s9y/Serendipity to 2.6.0.

Affected software

ProductAffectedFixed in
s9ySerendipityAffected
  • <2.6.0
Fixed in
  • 2.6.0
GitHubs9y/Serendipitypkg:github/s9y/SerendipityOther threatsAffected
  • <2.6.0
Fixed in
  • 2.6.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Serendipity to version 2.6.0 or later, where this vulnerability is fixed. Since the vendor advisory indicates the issue is resolved in 2.6.0, applying this official fix is the recommended remediation. Patch status is confirmed by the vendor's versioning information. No additional mitigation steps are specified.

Description

Serendipity versions prior to 2.6.0 contain a vulnerability where the function serendipity_setCookie() uses the HTTP Host header without validation when setting cookies. This allows an attacker who can manipulate the Host header during login to cause authentication cookies to be scoped to an attacker-controlled domain. The vulnerability enables session fixation, token leakage, and potential privilege escalation if an administrator logs in under a manipulated Host header. The issue is fixed in version 2.6.0.

References

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