CVE-2026-57580
CRITICALDescription
authentik is an open-source identity provider. Prior to 2026.2.6 and 2026.5.5, an inbound SAML Source configured with the non-default USERNAME_LINK or EMAIL_LINK user-matching mode interprets an XML comment in a NameID differently from the identity provider's signed assertion. An attacker with an account on the source identity provider who can set the account's NameID can inject an XML comment that truncates the value used by authentik to the text before the comment while the signed assertion remains valid. A crafted NameID can therefore truncate to a victim's username or email and bind the attacker's external identity to the victim's existing account. This grants full takeover without the victim's password or the identity provider's private key, and the malicious link persists so later logins succeed without the comment. Sources using the default unique-identifier matching mode and authentik's outbound SAML Provider role are not affected. This issue is fixed in versions 2026.2.6 and 2026.5.5.
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 v4 Vector
Exploitability
Impact
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Exploit Intelligence
Low risk: more likely to be exploited than 37% of all known CVEs.
References
Related Vulnerabilities
Other CWE-436 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-63030 | Critical | 9.8 | 97% | KEV | Fix |
| CVE-2025-25292 | Critical | 9.8 | 65% | - | Fix |
| CVE-2022-37436 | Medium | 5.3 | 58% | - | Fix |
| CVE-2021-28474 | High | 8.8 | 51% | - | Fix |
| CVE-2025-25291 | Critical | 9.8 | 20% | - | Fix |
| CVE-2019-17596 | High | 7.5 | 4.7% | - | Fix |
Common questions
How do I fix CVE-2026-57580?
No published fix for CVE-2026-57580 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-57580 being actively exploited?
Not that we know of. CVE-2026-57580 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.44% is the estimated probability that it will be exploited in the next 30 days. That is higher than 37% of all scored CVEs.
How severe is CVE-2026-57580?
CVE-2026-57580 has a CVSS v4 base score of 9.4, rated critical. 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 2026-08-18.