The parsing team has fixed a security bug in Parsoid [1].

* Users could send invalid prefixes, formats, or domains and run javascript code on the error page that Parsoid displayed.

* This fix has been applied to the Wikimedia cluster [2] and also merged into Parsoid master [1].

* We have also released a 0.5.3 deb version with this patch applied. [3]

* We have also released a 0.5.3 npm version of Parsoid. [4]

* Parsoid is a stateless service and doesn't retain any state between requests. In private wikis, VisualEditor can be configured to forward the user cookie to Parsoid to pass along to the MediaWiki API to parse a page, but this exploit is not exposed through VE.

In addition, Parsoid doesn't receive any user credentials on public wikis.

* However, if a wiki's Parsoid service is publicly accessible on the internet *and* is accessible through the wiki's domain, then, this exploit can be used to leak user cookies for that wiki. For all wikis that use Parsoid in this fashion, we recommend they patch their Parsoid installation immediately.

* On the Wikimedia cluster, Parsoid is proxied behind RESTBase and is not public accessible and as such, this exploit wasn't available for an exploit to steal user sessions.

Thanks to the reporter of this exploit, Darian Patrick from the Security Team, Arlo Breault from the Parsing Team, Daniel Zahn and others from Ops for their assistance handling this bug and preparing this release.

[1] https://gerrit.wikimedia.org/r/#/c/319115 [2] https://www.mediawiki.org/wiki/Parsoid/Deployments#Monday.2C_October_31.2C_2... [3] https://releases.wikimedia.org/debian/pool/main/p/parsoid/ [4] https://www.npmjs.com/package/parsoid

Subramanya Sastry, Technical Lead and Manager, Parsing Team, Wikimedia Foundation.