CVE-2026-40165
HIGHDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Exploit Intelligence
Moderate risk: more likely to be exploited than 40% of all known CVEs.
References
Related Vulnerabilities
Other CWE-91 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2020-0646 | Critical | 9.8 | 99% | KEV | - |
| CVE-2023-27253 | High | 8.8 | 90% | - | - |
| CVE-2023-46214 | High | 8.0 | 89% | - | Fix |
| CVE-2024-53675 | High | 7.3 | 84% | - | Fix |
| CVE-2024-53674 | High | 7.3 | 47% | - | Fix |
| CVE-2023-43187 | Critical | 9.8 | 45% | - | Fix |
Common questions
How do I fix CVE-2026-40165?
No published fix for CVE-2026-40165 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-40165 being actively exploited?
Not that we know of. CVE-2026-40165 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.50% is the estimated probability that it will be exploited in the next 30 days. That is higher than 40% of all scored CVEs.
How severe is CVE-2026-40165?
CVE-2026-40165 has a CVSS v3 base score of 8.7, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-23.