Missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion.
The issue is fixed by #9321.
Depending on the needs and configuration of the homeserver a few options are available:
email setting.account_threepid_delegates.msisdn is not configured.Additionally, the affected endpoint patterns can be blocked at a reverse proxy:
^/_matrix/client/(r0|unstable)/register/email^/_matrix/client/(r0|unstable)/register/msisdn^/_matrix/client/(r0|unstable)/account/password^/_matrix/client/(r0|unstable)/account/3pid{
"github_reviewed_at": "2021-04-12T21:01:40Z",
"github_reviewed": true,
"cwe_ids": [
"CWE-20"
],
"severity": "MODERATE",
"nvd_published_at": "2021-04-12T21:15:00Z"
}