GHSA-vhr5-g3pm-49fm

Description

### Impact A malicious homeserver can craft a room or room structure such that the predecessors form a cycle. The matrix-js-sdk's `getRoomUpgradeHistory` function will infinitely recurse in this case, causing the code to hang. This method is public but also called by the 'leaveRoomChain()' method, so leaving a room will also trigger the bug. Even if the CVSS score would be 4.1 ([AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:N/A:L](https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:N/A:L&version=3.1)) we classify this as High severity issue. ### Patches This was patched in matrix-js-sdk 34.3.1. ### Workarounds Sanity check rooms before passing them to the matrix-js-sdk or avoid calling either `getRoomUpgradeHistory` or `leaveRoomChain`. ### References N/A.