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Vulnerability record · CVE-2026-40165 · published 21 May 2026

CVE-2026-40165: XML injection vulnerability

authentik 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.

8.7 CVSS 3.1 High EPSS 0.68% · top 49.6% CWE-91 · XML injectionCWE-287 · Improper authentication Deferred
8.7CVSS 3.1 base score
0.68%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
23 Jul 2026Last modified by NVD

Description

authentik 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.

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

References

LinkTags
https://github.com/goauthentik/authentik/commit/47dec5c6b7fb4a62bfad2ae8bddf002bde7ba774
https://github.com/goauthentik/authentik/releases/tag/version%2F2025.12.5
https://github.com/goauthentik/authentik/security/advisories/GHSA-9wj8-xv4r-qwrp

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Source: NIST National Vulnerability Database (record CVE-2026-40165), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.