CVE-2026-34090 Suggested investigations: Handle suppressed usernames

Medium 4.8 Published 11 May 2026 Updated 11 May 2026

An attacker can view suppressed usernames, exposing sensitive user data in the Wikimedia CheckUser extension.

Exploited in the wild: Not known
Login needed: An administrator
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2026-34090?

CVE-2026-34090 is a medium-severity vulnerability in Wikimedia Foundation CheckUser, published on 11 May 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

Official description

Exposure of Sensitive Information to an Unauthorized Actor vulnerability in Wikimedia Foundation CheckUser.

This issue affects CheckUser: from 1.45.0 before 1.45.2.

Weakness: CWE-200

Which versions are affected by CVE-2026-34090?

It affects 1 product.

Products include Mediawiki Checkuser.

How do I fix CVE-2026-34090?

No fix has been published for CVE-2026-34090 yet. Limit exposure of the affected software until one is available.

Is CVE-2026-34090 being exploited?

There is no known exploitation of CVE-2026-34090 in the wild and no public exploit code.

Sources

Also known as GHSA-cg3w-6fh3-65mw.