# CVE-2025-53479: CheckUser: Reflected Cross-Site Scripting (XSS) in Special:CheckUser via unsanitized internationalized message

> Attackers can execute arbitrary JavaScript in victims' browsers via reflected XSS in the CheckUser interface, potentially leading to session hijacking.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Jul 2025
- **Updated:** 10 Jul 2025
- **Also known as:** GHSA-mjwg-jq5c-p8xr

## What is CVE-2025-53479?

CVE-2025-53479 is a medium-severity cross-site scripting vulnerability in Wikimedia Foundation Mediawiki - CheckUser extension, published on 8 Jul 2025. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

The CheckUser extension’s Special:CheckUser interface is vulnerable to reflected XSS via the rev-deleted-user message. This message is rendered without proper escaping, making it possible to inject JavaScript through the uselang=x-xss language override mechanism.

This issue affects Mediawiki - CheckUser extension: from 1.42.X before 1.42.7, from 1.43.X before 1.43.2.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2025-53479?


## How do I fix CVE-2025-53479?

No fix has been published for CVE-2025-53479 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-53479 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-53479 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-53479 and fix it if it is affected.

What it is: CVE-2025-53479 is a medium-severity cross-site scripting vulnerability in Wikimedia Foundation Mediawiki - CheckUser extension, published on 8 Jul 2025. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-53479 exists.

Affected product: Wikimedia Foundation Mediawiki - CheckUser extension. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2025-53479/ (Markdown: https://insights.sbomify.com/CVE-2025-53479/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-53479
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-53479
- OSV: https://osv.dev/vulnerability/CVE-2025-53479

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-53479/
Summaries are generated and may contain mistakes; the official description above is the record.