Input validation error in authentik - CVE-2026-40165
Published: May 12, 2026
Vulnerability identifier: #VU131247
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-40165
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Authentik Security Inc
Affected software:
authentik
authentik
Detailed vulnerability description
The vulnerability allows a remote attacker to gain access to other user accounts.
The vulnerability exists due to improper input validation in the SAML NameID value extraction logic when processing a SAML assertion. A remote attacker can inject an XML comment into the NameID value to gain access to other user accounts.
Exploitation requires an authentik instance configured with a SAML Source, XML signing enabled, and an attacker-controlled account on the SAML Source that can modify its NameID value.
How to mitigate CVE-2026-40165
Install security update from vendor's website.