GHSA-p2x4-6ghr-6vmq

Impact

User without the right to view documents can deduce their existence by repeated Livetable queries.

Reproduction steps

1. Restrict "view" access to Sandbox.TestPage3 by setting an explicit view right for admins
2. As a user who is not an admin, open <server>/bin/get/XWiki/LiveTableResults?outputSyntax=plain&classname=&collist=doc.title%2Cdoc.location%2Cdoc.content&doc.title=Sandbo&doc.location=Sandbox.TestPage3&doc.content=dummy&limit=0 where <server> is the URL of your XWiki installation.

Expect Result:

No results are displayed as the user doesn't have view rights on Sandbox.TestPage3.

Actual Result:

The result

{
  "reqNo": null,
  "matchingtags": {},
  "tags": [],
  "totalrows": 1,
  "returnedrows": 0,
  "offset": 1,
  "rows": [
    {
      "doc_viewable": false,
      "doc_fullName": "obfuscated"
    }
  ]
}

is displayed.

This reveals that a document Sandbox.TestPage3 exists (we explicitly searched for this name) which has a title containing "Sandbo" and a content containing "dummy". By starting with a single letter and then iteratively extending the match, the full content of the title/content or XObject properties can be discovered. Several tests can be combined in a single request to use binary search to narrow down the actual match from a list of possible characters/words. If the used alphabet is known and smaller than 128 distinct characters, it is possible to discover one character with 7 requests. Alternatively, frequencies of words and word pairs (2-gram frequencies) can be used to first guess whole words and only resort to guessing individual characters if none of the predicted words match, allowing a much faster recovery of the textual content. As it also depends on the content how easy the attack is and how much recovered content would be a "successful" attack, it is hard to quantify how many requests are necessary.

Patches

The issue has been patched in XWiki 14.6RC1, 13.10.8, and 14.4.3, the response is not properly cleaned up of obfuscated entries.

Workarounds

The patch for the document XWiki.LiveTableResultsMacros can be manually applied or a XAR archive of a patched version can be imported, on versions >= 12.10.11, >= 13.9-rc-1, and >= 13.4.4.

References

• https://github.com/xwiki/xwiki-platform/commit/1450b6e3c69ac7df25e5a2571186d1f43402facd#diff-5a739e5865b1f1ad9d79b724791be51b0095a0170cc078911c940478b13b949a
• https://jira.xwiki.org/browse/XWIKI-19999

For more information

If you have any questions or comments about this advisory:

• Open an issue in Jira XWiki.org
• Email us at Security Mailing List