Executive brief
Semantic MediaWiki's Special:Ask search interface accepts user-supplied pagination tokens that are not properly validated or encoded before display. An attacker can craft a malicious link containing JavaScript code in the pagination token, which executes in a victim's browser when the page loads, potentially stealing credentials or wiki data. No authentication is required; the attack is delivered via a simple phishing link.
Technical details
The vulnerability is a reflected cross-site scripting (XSS) flaw in the Special:Ask page's cursor-based pagination mechanism. The `cursor` query parameter is a base64url-encoded JSON blob that is decoded without signature verification, allowing an attacker to forge arbitrary content. When the cursor's sort parameters do not match the request sort parameters, the code builds an error message by directly interpolating the attacker-controlled `sort_prop` and `sort_order` fields into a raw string via `Query::addErrors()`, bypassing the normal message sanitization layer. This unsanitized error text is then passed to `Html::errorBox()` which emits it as raw HTML without output encoding. The attack requires only network access and a crafted URL; the victim must click the link. The fix involves output-encoding the `sort_prop` and `sort_order` values before interpolation into error messages.
Affected products
- Semantic MediaWiki Semantic MediaWiki 7.0.0 and later
Timeline
- 2026-09-18: disclosed
- 2026-09-18: advisory: GHSA-cx86-7xwp-w9wf