Envoy crashes when HTTP ext_proc processes local replies

Summary

Envoy's ext_proc HTTP filter is at risk of crashing if a local reply is sent to the external server due to the filter's life time issue. A known situation is the fail of a websocket handshake will trigger a local reply leading to the crash of Envoy.

PoC

If both websocket and ext_proc are enabled, a failed handshake will trigger a local reply, thus ext_proc will crash.

Mitigation

1. Disable websocket traffic
2. Change the websocket response from backend to always return 101 Switch protocol based on RFC.
3. Apply the patch and the ext_proc filter will not send the local reply that is generated by Envoy to the ext_proc server for processing.
4. Apply the patch that the router will cancel the upstream requests when sending a local reply.

Impact

Denial of service

Reporter

Vasilios Syrakis Fernando Cainelli