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Forward authentication bypass with malformed session cookie on Traefik and Caddy

High
rissson published GHSA-fj56-5763-j8pp Feb 12, 2026

Package

authentik

Affected versions

<= 2025.10.3
<= 2025.12.3

Patched versions

2025.10.4
2025.12.4

Description

Summary

With a malformed cookie it was possible to bypass authentication when using forward authentication in the authentik Proxy Provider when used in conjunction with Traefik or Caddy as reverse proxy. When a malicious cookie was used, none of the authentik-specific X-Authentik-* headers were set which depending on application can grant access to an attacker.

Patches

authentik 2025.10.4 and 2025.12.4 fix this issue.

Impact

Depending on the behavior of applications (based on if they require an X-Authentik header being present) behind the Proxy Provider, attackers are potentially able to gain full access to the application.

Workarounds

There are no workarounds. If an upgrade is not possible, it is recommended to deactivate the reverse proxy entries for any applications using forward authentication until authentik can be upgraded.

For more information

If you have any questions or comments about this advisory:

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

CVE ID

CVE-2026-25748

Weaknesses

Improper Authentication

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Learn more on MITRE.

Credits