GHSA-w4pr-4vjg-hffh When matrix-nio receives forwarded room keys, the receiver doesn't check if it requested the key from the forwarder

• PyPI matrix-nio: < 0.20 → fixed in 0.20

When matrix-nio before 0.20 requests a room key from our devices, it correctly accepts key forwards only if they are a response to a previous request. However, it doesn't check that the device that responded matches the device the key was requested from. This allows a malicious homeserver to insert room keys of questionable validity into the key store in some situations, potentially assisting in an impersonation attack. For more information If you have any questions or comments about this advisory, e-mail us at [email protected].