The component jitsi-meet-prosody (version <= 1.0.4985-1) was shipped with an insecure default configuration in prosody.cfg.lua that allowed malicious unauthenticated users to gain moderator privileges prior to the start of a meeting.
The way of working remotely changed drastically with COVID. A lot of products were made quickly available which aimed to fill the gap of meeting people face to face via the Internet using a webcam.
But there was a problem: most of these products were centralized, and all communications (chat, video, audio or file share) were traveling to and from the company’s servers.
To obviate this issue, one product in particular gained a lot of attention: Jitsi, the open-source privacy-focused video chat with easy self-hosting capabilities.
With more than 300 contributors on GitHub, the project is quickly growing and being used by a lot of companies for private communications.
The configuration files were amended in accordance with the official documentation (https://jitsi.github.io/handbook/docs/devops-guide/secure-domain) to enable authentication, therefore only moderators could start a new meeting.
The use case for this authentication bypass is:
The main muc component available at “conference.<yourdomain>.ltd” was missing the ‘restrict_room_creation’ directive, which allowed unauthenticated participants to force the conference to start and gain moderator privileges.
The pull request that fixed this issue can be seen at https://github.com/jitsi/jitsi-meet/pull/9252/files.
When Jitsi is configured to require the host to login, the following UI message is presented to the participants before the meeting can start:
The XMPP BOSH requests and responses, while waiting for the host to open the room, are as follow:
The next step to trigger the vulnerability, is to make the client (browser) believe that the server accepted its authentication request (which was never sent in the first place). This can be achieved by tampering with one of the “not authorized” responses to insert the following content:
It is important to change the following elements to make a valid response:
Also, this issue can only be triggered if the response from the server is tampered with in a timely manner. For this reason, it is strongly advised to let Burp Suite change the response via Match and Replace functionality:
Let’s take a look at what’s happening in the requests/responses once the client receives the tampered response.
Table 2: Client sends a <presence> structure and Server assigns moderator privileges to the attacker.
At this stage the attacker is the first one in the room, however the room is still closed for all other participants as we need to wait for a moderator to login to see people joining the same space. It should be noted that the attacker moderator does not have the necessary privileges to start the meeting – that action can only be performed by the legitimate moderator.
Once a legitimate moderator has joined, this will be the view from the attacker perspective:
The attacker, having moderator role, can enable the lobby, set a room password, mute, stop video, chat, and generally perform all moderator actions.
Please note: Moderators cannot kick out another moderator – which will make the attacker presence in the room permanent.
Updating to the newly released version of jitsi-meet-prosody will resolve this issue, which at the time of writing is 2.0.5963-1.
20/05/2021: Bug Identified
21/05/2021: Technical documentation delivered to Jitsi developers privately and CVE request submitted
21/05/2021: A fix is issued in the commit https://github.com/jitsi/jitsi-meet/pull/9252/commits/5568dacf893116c8056f4aa1fea7baaf414d1947
25/05/2021: Commit pushed into master branch
10/06/2021: New release of jitsi-meet-prosody
18/06/2021: Jitsi release advisory: https://github.com/jitsi/security-advisories/blob/master/advisories/JSA-2021-0001.md
27/07/2021: Publishing this blog post
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