CVE-2026-39963Public exploitNetwork attack vector

Authentication token theft via Host-derived cookie domains

Published Apr 14, 2026 · Updated Apr 14, 2026

Host header injection in Serendipity before 2.6.0 allows remote attackers to steal authentication tokens through poisoned cookie domains. serendipity_setCookie() passes the unvalidated HTTP Host header to setcookie() as the domain for session and auto-login cookies. Exploitation requires control of the Host header while a user logs in, exposing that user's tokens and enabling account takeover at the user's privilege level.

CVSS severity6.9
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Host header injection in Serendipity before 2.6.0 allows remote attackers to steal authentication tokens through poisoned cookie domains. serendipity_setCookie() passes the unvalidated HTTP Host header to setcookie() as the domain for session and auto-login cookies. Exploitation requires control of the Host header while a user logs in, exposing that user's tokens and enabling account takeover at the user's privilege level.

The record

CVE
CVE-2026-39963
Published
Apr 14, 2026
Updated
Apr 14, 2026
Vendor
Serendipity Team
Product
Serendipity
Classifications
CWE-565, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Serendipity Team · Serendipityversion=< 2.6.0

Published CVSS scores

6.9GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-565Reliance on Cookies without Validation and Integrity Checking
T1539Steal Web Session Cookie

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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