Rocket.Chat in versions before 8.8.0, 8.7.1, 8.6.2, 8.5.3, 8.4.6. 8.3.8, 8.2.8, 8.1.8, and 7.10.15, the Meteor DDP methods getThreadsList an

Rocket.Chat in versions before 8.8.0, 8.7.1, 8.6.2, 8.5.3, 8.4.6. 8.3.8, 8.2.8, 8.1.8, and 7.10.15, the Meteor DDP methods getThreadsList and getThreadMessages accept rid / tmid as raw, untyped parameters with no schema validation. A MongoDB operator object (e.g. {"$gt": "4"}) can be substituted for a string room-id or message-id. The authorization check resolves to a room the attacker already has access to, while the downstream data query fans out across all rooms - disclosing private thread parents and their full reply content to any low-privilege authenticated user.
The REST route chat.getThreadsList was patched in v5.0 (HackerOne report #1446767) by adding rid: {type:'string'} AJV validation. The equivalent DDP method was never given the same fix and remains exploitable