CVE-2025-66622: matrix-sdk-base is vulnerable to DoS via custom m.room.join_rules event values
matrix-sdk-base is the base component to build a Matrix client library. Versions 0.14.1 and prior are unable to handle responses that include custom m.room.joinrules values due to a serialization bug. This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventing further processing for all rooms. This is fixed in version 0.16.0.
Other sources
The matrix-sdk-base crate is unable to handle responses that include custom m.room.joinrules values due to a serialization bug.
This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventing further processing for all rooms.
Patches The issue is fixed in matrix-sdk-base 0.16.0.
Workarounds
Users can leave affected rooms on another client to mitigate the issue.
References
The issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/5924.
— GitHub
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2025-66622?
CVE-2025-66622 has been classified as a denial-of-service vulnerability due to its ability to stall the sync process.
How do I fix CVE-2025-66622?
To mitigate CVE-2025-66622, upgrading to matrix-sdk-base version 0.16.0 or later is recommended.
What causes CVE-2025-66622?
CVE-2025-66622 is caused by a serialization bug that affects the handling of custom m.room.join_rules values.
What software is affected by CVE-2025-66622?
CVE-2025-66622 affects the matrix-sdk-base crate prior to version 0.16.0.
What happens if I am impacted by CVE-2025-66622?
If impacted by CVE-2025-66622, users may experience denied service due to stalled sync processes when invited to rooms with non-standard join rules.