# 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.

- **Severity:** Low 2.9 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jun 2026
- **Updated:** 22 Jun 2026
- **Also known as:** GHSA-hjj4-hfjm-fmrj, GO-2026-5430

## 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.

Weakness: CWE-307 (Improper Restriction of Excessive Authentication Attempts), CWE-178 (Improper Handling of Case Sensitivity)

## 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 | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47203 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-47203 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/authelia/authelia/v4 (Go): affected from 4.38.0; fixed in 4.39.20
- github.com/authelia/authelia/v4 (Go): affected from 4.38.0; fixed in 4.39.20
- github.com/authelia/authelia/v4 (Go): affected from 4.38.0; fixed in 4.39.20
- github.com/authelia/authelia (Go): affected all versions; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-47203/ (Markdown: https://insights.sbomify.com/CVE-2026-47203/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47203
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47203
- OSV: https://osv.dev/vulnerability/CVE-2026-47203

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47203/
Summaries are generated and may contain mistakes; the official description above is the record.