CVE-2026-47774: Envoy vulnerable to HTTP/2 memory exhaustion via cookie header size bypass and H

Official description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a vulnerability in Envoy's HTTP/2 downstream request processing allows an unauthenticated remote client to trigger excessive memory consumption, potentially resulting in OOM termination of the Envoy process and denial of service. The issue arises from the combination of two behaviors. First, cookie header bytes are not fully accounted for during request header size validation in Envoy. Second, HPACK header block limits in oghttp2/quiche are enforced on encoded bytes without a corresponding limit on total decoded header size. Together, these behaviors allow a malicious client to cause large decoded header allocations while bypassing the intended request header size protections. Versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1 contain a fix. No complete workaround is known short of applying a fix. Possible temporary mitigations include disabling downstream HTTP/2 where operationally feasible; enforcing stricter request header and cookie limits before traffic reaches Envoy; and monitoring Envoy memory usage for abnormal growth under HTTP/2 traffic.

Vendor	Product	Versions
envoyproxy	envoy	< 1.35.11>= 1.36.0, < 1.36.7>= 1.37.0, < 1.37.3>= 1.38.0, < 1.38.1

Vendor

Product

Versions

envoyproxy

envoy

< 1.35.11>= 1.36.0, < 1.36.7>= 1.37.0, < 1.37.3>= 1.38.0, < 1.38.1

CVE-2026-47774Envoy vulnerable to HTTP/2 memory exhaustion via cookie header size bypass and HPACK amplification

In plain English

Official description

Affected products (as reported)

References