CVE-2022-39374: Synapse Denial of service due to incorrect application of event authorization rules during state resolution
Impact If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected.
Synapse homeservers are affected by this issue if and only if they are joined to rooms which members of untrusted homeservers are joined or invited to.
- Synapse homeservers in rooms available over public federation are affected. - Synapse homeservers with federation disabled are not affected. - Synapse homeservers in a closed federation containing only trusted servers are not affected. - Synapse homeservers which are only joined to rooms with federation disabled[^1] are not affected.
Patches Administrators of homeservers with federation enabled are advised to upgrade to 1.68.0 or higher.
Workarounds Federation can be disabled by setting federationdomainwhitelist to an empty list ([]). from the vulnerable homeserver to be rejected. This issue has been patched in version 1.68.0
References - https://github.com/matrix-org/synapse/pull/13723
[^1]: See m.federate in the m.room.create definition.
For more information
If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
Other sources
If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected.
Synapse homeservers are affected by this issue if and only if they are joined to rooms which members of untrusted homeservers are joined or invited to.
- Synapse homeservers in rooms available over public federation are affected. - Synapse homeservers with federation disabled are not affected. - Synapse homeservers in a closed federation containing only trusted servers are not affected. - Synapse homeservers which are only joined to rooms with federation disabled1 are not affected.
— Red Hat
Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected. This issue has been patched in version 1.68.0
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is CVE-2022-39374?
CVE-2022-39374 is a vulnerability in Synapse, an open-source Matrix homeserver, that allows a malicious homeserver to trick Synapse into accepting previously rejected events into its view of the current state of a room.
How does CVE-2022-39374 impact Synapse?
CVE-2022-39374 allows a malicious homeserver to cause all further messages and state changes to be accepted by Synapse.
What is the severity of CVE-2022-39374?
The severity of CVE-2022-39374 is medium, with a CVSS score of 6.5.
What software versions are affected by CVE-2022-39374?
Versions of matrix-synapse between 1.62.0 and 1.68.0 are affected by CVE-2022-39374.
How can I fix CVE-2022-39374?
To fix CVE-2022-39374, you should update matrix-synapse to version 1.68.0 or higher.