# CVE-2026-39839: Wikimedia MediaWiki Cargo Extension stored XSS in map format

Source: https://junglewise.ai/threats/cve-2026-39839-wikimedia-mediawiki-cargo-extension-stored-xss-in-map-format  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-07. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-39839 · Severity: medium · CVSS 6.1 · Published 2026-04-07

The Cargo extension for MediaWiki, which allows for the storage and querying of structured data, contains a security flaw that allows for stored cross-site scripting (XSS). An attacker can inject malicious scripts into map-based data displays by using specially crafted links. If a user views the affected map and clicks on the malicious link, the script could execute in their browser, potentially leading to unauthorized actions or data theft.

Technologies: [Wikimedia Foundation Cargo Extension](https://junglewise.ai/threats/technologies/cargo-extension). Vendors: [Wikimedia Foundation](https://junglewise.ai/threats/vendors/wikimedia-foundation).

## Quick answers

**Is CVE-2026-39839 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39839 being exploited in the wild.

**How severe is CVE-2026-39839?** Medium severity, with a CVSS score of 6.1, published 7 April 2026.

**Which products and versions are affected?** Wikimedia Foundation Cargo Extension before 3.8.7.

**Is there a fix for CVE-2026-39839?** A patch was published on 2026-02-09: Fixes merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-39839 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-39839?** Check whether you run Wikimedia Foundation Cargo Extension 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

A stored cross-site scripting (XSS) vulnerability exists in the Cargo extension for MediaWiki due to improper neutralization of script-related HTML tags in the 'map' output format. Specifically, the extension fails to validate URLs used within map markers, allowing an attacker to store a 'javascript:' URI. When a user interacts with a marker containing this malicious link on a Cargo-generated map, the script executes in the context of the user's session. This issue is tracked as CWE-80 and was resolved in version 3.8.7 by adding URL validation to the CargoMapsFormat.php component.

## Affected products

- Wikimedia Foundation MediaWiki - Cargo Extension before 3.8.7

## Timeline

- 2026-02-03: disclosed: Vulnerability reported via Phabricator task T416271
- 2026-02-09: patched: Fixes merged into master branch
- 2026-04-07: advisory: CVE-2026-39839 published

## References

- [https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cargo/+/1237957](https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cargo/+/1237957)
- [https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cargo/+/1237977](https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Cargo/+/1237977)
- [https://phabricator.wikimedia.org/T416271](https://phabricator.wikimedia.org/T416271)

## Related threats

- [Wikimedia MediaWiki Cargo Extension stored XSS in map format](https://junglewise.ai/threats/cve-2026-58519-wikimedia-mediawiki-cargo-extension-stored-xss-in-map-format)
- [Wikimedia MediaWiki Cargo Extension stored XSS in list fields](https://junglewise.ai/threats/cve-2026-39841-wikimedia-mediawiki-cargo-extension-stored-xss-in-list-fields)
- [Wikimedia MediaWiki Cargo Extension stored XSS in dynamic table format](https://junglewise.ai/threats/cve-2026-39837-wikimedia-mediawiki-cargo-extension-stored-xss-in-dynamic-table)