Impact
This vulnerability allowed a malicious user to serve arbitrary HTML files from the main application domain (readthedocs[.]org/readthedocs[.]com) by exploiting a vulnerability in the code that serves downloadable content from a project.
Exploiting this would have required the attacker to get a logged-in user to visit the malicious URL, which would have allowed the attacker to take control of the user’s session with JavaScript (making requests to the API/site on behalf of the user). This URL would have looked something like hxxps[:]//readthedocs[.]org/projects/attacker-project/downloads/html/version-with-javascript-attack/.
Patches
This issue has been patched in our 8.8.1 release.