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GHSA-7rfg-6273-f5wp
No affected components available
Impact
The rendered diff in XWiki embeds images to be able to compare the contents and not display a difference for an actually unchanged image. For this, XWiki requests all embedded images on the server side. These requests are also sent for images from other domains and include all cookies that were sent in the original request to ensure that images with restricted view right can be compared. This allows an attacker to steal login and session cookies that allow impersonating the current user who views the diff. The attack can be triggered with an image that references the rendered diff, thus making it easy to trigger.
More concretely, to reproduce, add 101 different images with references to the attacker's server. In any place add an image with a reference to /xwiki/bin/view/Image%20Cookie%20Test/?xpage=changes&rev1=1.1&rev2=2.1&include=renderedChanges where Image%20Cookie%20Test needs to be replaced by the path to the document with the images and the two revisions should match the revision before/after adding the images. Whenever a user views that image, the user's login cookies should be sent to the attacker's server. The 101 images are to circumvent the cache that has a default maximum size of 100 entries.
Apart from stealing login cookies, this also allows server-side request forgery (the result of any successful request is returned in the image's source) and viewing protected content as once a resource is cached, it is returned for all users. As only successful requests are cached, the cache will be filled by the first user who is allowed to access the resource.
Patches
This has been patched in XWiki 14.10.15, 15.5.1 and 15.6. The rendered diff now only downloads images from trusted domains. Further, cookies are only sent when the image's domain is the same the requested domain. The cache has been changed to be specific for each user.
Workarounds
As a workaround, the image embedding feature can be disabled by deleting xwiki-platform-diff-xml-<version>.jar in WEB-INF/lib/.
References
- https://jira.xwiki.org/browse/XWIKI-20818
- https://github.com/xwiki/xwiki-platform/commit/bff0203e739b6e3eb90af5736f04278c73c2a8bb
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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