# CVE-2026-34090: Wikimedia Foundation CheckUser information exposure in Suggested Investigations

Source: https://junglewise.ai/threats/cve-2026-34090-wikimedia-foundation-checkuser-information-exposure-in-suggested  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-11. Updated: 2026-05-14  
License: CC BY 4.0 with a link back

CVE-2026-34090 · Severity: high · CVSS 7.5 · Published 2026-05-11

A vulnerability in the CheckUser extension for MediaWiki could allow unauthorized users to view suppressed or hidden usernames. CheckUser is a tool used by wiki administrators to investigate disruptive behavior and maintain site integrity. If exploited, this flaw could lead to the exposure of sensitive identity information that was intended to be restricted from public or low-level administrative view.

Technologies: [Wikimedia Foundation CheckUser](https://junglewise.ai/threats/technologies/checkuser). Vendors: [Wikimedia Foundation](https://junglewise.ai/threats/vendors/wikimedia-foundation).

## Quick answers

**Is CVE-2026-34090 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34090 being exploited in the wild.

**How severe is CVE-2026-34090?** High severity, with a CVSS score of 7.5, published 11 May 2026.

**Which products and versions are affected?** Wikimedia Foundation CheckUser 1.45.0 to 1.45.1, from 1.45.0 before 1.45.2.

**Is there a fix for CVE-2026-34090?** A patch was published on 2026-02-13: Patch developed and reviewed Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-34090 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-34090?** Check whether you run Wikimedia Foundation CheckUser at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An information disclosure vulnerability (CWE-200) exists in the Wikimedia Foundation CheckUser extension within the Special:SuggestedInvestigations component. The application fails to properly filter or redact suppressed usernames, making them visible to users who lack the specific permissions required to view hidden user data. This issue affects CheckUser versions 1.45.0 through 1.45.1. An attacker with high-privileged access (but lacking specific suppression-viewing rights) could exploit this to identify accounts that have been hidden from the public. The vulnerability is addressed in version 1.45.2.

## Affected products

- Wikimedia Foundation CheckUser from 1.45.0 before 1.45.2

## Timeline

- 2025-12-01: disclosed: Issue reported internally via Phabricator
- 2026-02-13: patched: Patch developed and reviewed
- 2026-05-11: advisory: CVE-2026-34090 published

## References

- [https://phabricator.wikimedia.org/T411366](https://phabricator.wikimedia.org/T411366)

## Related threats

- [Wikimedia Foundation CheckUser XSS in blockConnectedTempAccountsField](https://junglewise.ai/threats/cve-2026-58034-wikimedia-foundation-checkuser-xss-in)