# CVE-2026-103439: Wikimedia MediaWiki Wikbase cross-site scripting in HTML tags

Source: https://junglewise.ai/threats/cve-2026-103439-improper-neutralization-of-script-related-html-tags-in-a-web  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-30. Updated: 2026-09-30  
License: CC BY 4.0 with a link back

CVE-2026-103439 · Severity: info · Published 2026-09-30

The Wikimedia Foundation's MediaWiki Wikbase extension contains a cross-site scripting (XSS) vulnerability that allows improper handling of HTML script tags in web pages. An attacker could inject malicious scripts into affected pages, potentially compromising user sessions, stealing credentials, or defacing wiki content. This affects multiple versions of the Wikbase extension used by wiki installations worldwide.

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

## Quick answers

**Is CVE-2026-103439 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103439 being exploited in the wild.

**How severe is CVE-2026-103439?** Informational severity, published 30 September 2026.

**Which products and versions are affected?** Wikimedia Foundation MediaWiki Wikbase 1.43, 1.45, 1.46.

**Is there a fix for CVE-2026-103439?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-103439 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-103439?** Check whether you run Wikimedia Foundation MediaWiki Wikbase 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

The vulnerability is an improper neutralization of script-related HTML tags resulting in basic XSS, affecting the Wikbase extension for MediaWiki versions 1.43, 1.45, and 1.46. The flaw allows attackers to inject and execute arbitrary JavaScript in the context of wiki pages, typically via page content or parameters that are not properly sanitized. Patches have been made available through the Wikimedia Gerrit repository.

## Affected products

- Wikimedia Foundation MediaWiki Wikbase 1.43, 1.45, 1.46

## Timeline

- 2026-09-30: disclosed

## References

- [https://gerrit.wikimedia.org/r/q/Ie7a35b211565148e0cae437a4a8c41633b81f1b3](https://gerrit.wikimedia.org/r/q/Ie7a35b211565148e0cae437a4a8c41633b81f1b3)
- [https://phabricator.wikimedia.org/T182213](https://phabricator.wikimedia.org/T182213)