CVE-2026-47203: authelia Improper Handling of Case Sensitivity

Vulnerability summary

CVE-2026-47203 is a low (CVSS 2.9) Improper Handling of Case Sensitivity vulnerability in authelia. EPSS estimates a 0.45% chance of exploitation in the next 30 days, higher than 38% of scored vulnerabilities.

Timeline

1. 19-06-2026
   PublishedVulnerability first disclosed.
2. 22-06-2026
   Last modifiedVulnerability information updated.

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.

• CWE-178Improper Handling of Case SensitivityThe product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.
• CWE-307Improper Restriction of Excessive Authentication AttemptsThe product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame.