authentik: SAML NameID XML Comment Injection Enables Authentication Bypass via Identifier Truncation

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Summary

CVECVE-2026-40165
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-21 00:16:28 UTC
Updated2026-05-21 15:24:25 UTC
Descriptionauthentik is an open-source identity provider. Versions 2025.12.4 and prior, and versions 2026.2.0-rc1 through 2026.2.2 were vulnerable to Authentication Bypass through SAML NameID XML Comment Injection. Due to how authentik extracted the NameID value from a SAML assertion, it was possible for an attacker to trick authentik into only seeing a part of the NameID value, potentially allowing an attacker to gain access to other accounts. This issue could be exploited on an authentik instance with a SAML Source, where the attacker had an account on the SAML Source and the ability to modify their NameID value (commonly username or E-mail), and XML Signing was enabled. The attacker could modify the SAML assertion given to authentik by injecting a comment within the NameID value, which effectively truncated the NameID value to the snippet before the comment, and gave the attacker access to any user account. This issue has been fixed in versions 2025.12.5 and 2026.2.3.

Risk And Classification

Primary CVSS: v3.1 8.7 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

EPSS: 0.000200000 probability, percentile 0.056900000 (date 2026-05-27)

Problem Types: CWE-91 | CWE-287 | CWE-436 | CWE-287 CWE-287: Improper Authentication | CWE-91 CWE-91: XML Injection (aka Blind XPath Injection) | CWE-436 CWE-436: Interpretation Conflict

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.7HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
3.1CNADECLARED8.7HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Goauthentik Authentik affected < 2025.12.5 Not specified
CNA Goauthentik Authentik affected >= 2026.2.0-rc1, < 2026.2.3 Not specified

References

ReferenceSourceLinkTags
github.com/goauthentik/authentik/releases/tag/version%2F2025.12.5 [email protected] github.com
github.com/goauthentik/authentik/commit/47dec5c6b7fb4a62bfad2ae8bddf002b... [email protected] github.com
github.com/goauthentik/authentik/security/advisories/GHSA-9wj8-xv4r-qwrp [email protected] github.com
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