Executive brief
Envoy Proxy, a widely-used networking intermediary component for managing HTTP/3 connections, contains a flaw in QPACK header decompression that allows attackers to crash services handling HTTP/3 traffic. An attacker can send malformed requests that cause the HTTP/3 stack to stop responding, resulting in service unavailability for legitimate users.
Technical details
A vulnerability in Envoy Proxy's QPACK (QUIC Package Compression) decoder allows a network-based attacker to cause a denial-of-service condition in the HTTP/3 stack. The flaw occurs when the decoder encounters blocked QPACK streams, which can be triggered by specially crafted HTTP/3 requests. The vulnerability is reachable over the network from any client capable of sending HTTP/3 traffic to an affected Envoy instance; no authentication is required. Successful exploitation causes the HTTP/3 connection handler to fail, rendering the proxy unable to process legitimate traffic. Patches are available through Google Cloud Service Mesh updates.
Affected products
- Envoy Envoy Proxy <unknown>
Timeline
- 2026-06-29: disclosed