CVE-2026-47203 Authelia Missing Username Canonicalization in Basic Auth (LDAP)
Attackers can bypass account lockout mechanisms by varying username casing in Basic Auth requests, allowing unlimited brute-force attempts against LDAP users.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47203?
CVE-2026-47203 is a low-severity vulnerability in authelia, published on 19 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-47203?
4 open source packages ship an affected version, including github.com/authelia/authelia/v4 and github.com/authelia/authelia.
| Package | Affected | Fixed in |
|---|---|---|
github.com/authelia/authelia/v4 Go | From 4.38.0 | 4.39.20 |
github.com/authelia/authelia/v4 Go | From 4.38.0 | 4.39.20 |
github.com/authelia/authelia/v4 Go | From 4.38.0 | 4.39.20 |
github.com/authelia/authelia Go | All versions | None |
How do I fix CVE-2026-47203?
Upgrade github.com/authelia/authelia/v4 to 4.39.20 or later.
Is CVE-2026-47203 being exploited?
There is no known exploitation of CVE-2026-47203 in the wild and no public exploit code.
Sources
Also known as GHSA-hjj4-hfjm-fmrj, GO-2026-5430.