XWiki Platform Applications Tag and XWiki Platform Tag UI vulnerable to Eval Injection

Impact

The tags document Main.Tags in XWiki didn't sanitize user inputs properly, allowing users with view rights on the document (default in a public wiki or for authenticated users on private wikis) to execute arbitrary Groovy, Python and Velocity code with programming rights. This allows bypassing all rights checks and thus both modification and disclosure of all content stored in the XWiki installation. Also, this could be used to impact the availability of the wiki. Some versions of XWiki XML-escaped the tag (e.g., version 3.1) but this isn't a serious limitation as string literals can be delimited by / in Groovy and < and > aren't necessary, e.g., to elevate privileges of the current user.

On XWiki versions before 13.10.4 and 14.2, this can be combined with the authentication bypass using the login action, meaning that no rights are required to perform the attack. The following URL demonstrates the attack: <server>/xwiki/bin/login/Main/Tags?xpage=view&do=viewTag&tag=%7B%7Basync+async%3D%22true%22+cached%3D%22false%22+context%3D%22doc.reference%22%7D%7D%7B%7Bgroovy%7D%7Dprintln%28%22hello+from+groovy%21%22%29%7B%7B%2Fgroovy%7D%7D%7B%7B%2Fasync%7D%7D, where <server> is the URL of the XWiki installations.

On current versions (e.g, 14.3), the issue can be exploited by requesting the URL <server>/xwiki/bin/view/Main/Tags?do=viewTag&tag=%7B%7Basync%20async%3D%22true%22%20cached%3D%22false%22%20context%3D%22doc.reference%22%7D%7D%7B%7Bgroovy%7D%7Dprintln(%22hello%20from%20groovy!%22)%7B%7B%2Fgroovy%7D%7D%7B%7B%2Fasync%7D%7D, where <server> is the URL of the server. On XWiki 2.0 (that contains version 1.7 of the tag application), the URL <server>/xwiki/bin/view/Main/Tags?do=viewTag&tag={{/html}}{{groovy}}println(%2Fhello from groovy!%2F){{%2Fgroovy}} demonstrates the exploit while on XWiki 3.1 the following URL demonstrates the exploit: <server>/xwiki/bin/view/Main/Tags?do=viewTag&tag={{/html}}{{footnote}}{{groovy}}println(%2Fhello%20from%20groovy!%2F){{%2Fgroovy}}{{/footnote}}.

Patches

This has been patched in the supported versions 13.10.6 and 14.4.

Workarounds

The patch that fixes the issue can be manually applied to the document Main.Tags or the updated version of that document can be imported from version 14.4 of xwiki-platform-tag-ui using on XWiki 10.9 and later (earlier versions might not be compatible with the current version of the document).