CVE-2026-48521: Envoyproxy Envoy

Medium severity, CVSS 5.9. EPSS: 0.7% chance of exploitation in the next 30 days.

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transport_socket_options while selecting an HTTP/3 connection pool without first checking whether the pointer is null. LoadBalancerContext implementations used by synthetic, mirror, health-check, and async-client calls can return no transport-socket options. With auto_config and HTTP/3 enabled, routine traffic reaching one of those contexts can crash an Envoy worker. The relevant scope boundary is that the affected branch requires HTTP/3 in the protocol set and a context that supplies no transport-socket options. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Affected products

• Envoyproxy Envoy: before 1.36.10 (fixed in 1.36.10); from 1.37.0, before 1.37.6 (fixed in 1.37.6); from 1.38.0, before 1.38.4 (fixed in 1.38.4); from 1.39.0, before 1.39.1 (fixed in 1.39.1)

Published 2026-09-21. Last modified 2026-10-05.