GHSA-w9fg-xffh-p362

Denial of service (via resource exhaustion) due to improper input validation on third-party identifier endpoints

Source: GitHub Advisory Database (reviewed) Moderate CVE-2021-21394

Packages

Ecosystem	Package	Affected	Fixed in
PyPI	matrix-synapse	< 1.28.0	1.28.0

Details

As written in the advisory (Markdown source, shown as plain text).

### Impact 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. ### Patches The issue is fixed by #9321. ### Workarounds Depending on the needs and configuration of the homeserver a few options are available: 1. Using email as third-party identifiers be disabled by not configuring the `email` setting. 2. Using phone numbers as third-party identifiers can be disabled by ensuring that `account_threepid_delegates.msisdn` is not configured. 3. 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`

References

External links from the advisory. They lead to third-party sites.