CVE-2021-32780: Envoyproxy Envoy

High severity, CVSS 7.5. EPSS: 1.2% chance of exploitation in the next 30 days.

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions Envoy transitions a H/2 connection to the CLOSED state when it receives a GOAWAY frame without any streams outstanding. The connection state is transitioned to DRAINING when it receives a SETTING frame with the SETTINGS_MAX_CONCURRENT_STREAMS parameter set to 0. Receiving these two frames in the same I/O event results in abnormal termination of the Envoy process due to invalid state transition from CLOSED to DRAINING. A sequence of H/2 frames delivered by an untrusted upstream server will result in Denial of Service in the presence of untrusted **upstream** servers. Envoy versions 1.19.1, 1.18.4 contain fixes to stop processing of pending H/2 frames after connection transition to the CLOSED state.

Affected products

• Envoyproxy Envoy: from 1.18.0, before 1.18.4 (fixed in 1.18.4); version 1.19.0 only

Published 2021-08-24. Last modified 2026-06-17.