Sydent vulnerable to denial of service attack via memory exhaustion

Impact

Sydent does not limit the size of requests it receives from HTTP clients. A malicious user could send an HTTP request with a very large body, leading to disk space exhaustion and denial of service.

Sydent also does not limit response size for requests it makes to remote Matrix homeservers. A malicious homeserver could return a very large response, again leading to memory exhaustion and denial of service.

This affects any server which accepts registration requests from untrusted clients.

Patches

Patched by 89071a1, 0523511, f56eee3.

Workarounds

Request sizes can be limited in an HTTP reverse-proxy.

There are no known workarounds for the problem with overlarge responses.

For more information

If you have any questions or comments about this advisory, email us at security@matrix.org.