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CVE-2026-47203: Authelia Missing Username Canonicalization in Basic Auth (LDAP)

• Severity: low (CVSS 2.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-19 · updated 2026-06-23
• Weakness: CWE-178

Description

Authelia is an open-source authentication and authorization server providing two-factor authentication and single sign-on (SSO) for applications via a web portal. In versions 4.38.0 through 4.39.19, when a user authenticates via Basic Auth (i.e via the `Authorization` header with the `Basic` scheme) on the authz verification endpoint, Authelia takes the username directly from the `Authorization` header and passes it as is to the regulation system for ban checking and attempt recording. LDAP treats usernames case insensitively : `john`, `John`, and `JOHN` all bind as the same user. But the regulation SQL queries treat the lookup of these values in certain scenarios as case sensitive. This allows each variation of a usernames case to have its own ban bucket. Upgrade to 4.39.20 to receive a patch. As a workaround, explicitly disable the basic auth mechanism.

Affected products

• authelia: from 4.38.0, < 4.39.20

References

• https://github.com/authelia/authelia/commit/b8985b57b70acdff8f204ed426ff619e763461ad
• https://github.com/authelia/authelia/security/advisories/GHSA-hjj4-hfjm-fmrj

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