CVE-2026-40165: High authentication bypass (CVSS 8.7)

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 breakdown

Attack vectorNetwork

Attack complexityHigh

Privileges requiredNone

User interactionNone

ScopeChanged

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-40165 being actively exploited?

CVE-2026-40165 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.68%.

How severe is CVE-2026-40165?

CVE-2026-40165 has a CVSS 3.1 base score of 8.7, rated high. EPSS estimates a 0.68% probability of exploitation.

How do I fix CVE-2026-40165?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-40165 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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