CVE-2023-35945: Envoy vulnerable to HTTP/2 memory leak in nghttp2 codec

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-07-13 · updated 2026-10-15
Weakness: CWE-400

Description

Envoy is a cloud-native high-performance edge/middle/service proxy. Envoy’s HTTP/2 codec may leak a header map and bookkeeping structures upon receiving `RST_STREAM` immediately followed by the `GOAWAY` frames from an upstream server. In nghttp2, cleanup of pending requests due to receipt of the `GOAWAY` frame skips de-allocation of the bookkeeping structure and pending compressed header. The error return [code path] is taken if connection is already marked for not sending more requests due to `GOAWAY` frame. The clean-up code is right after the return statement, causing memory leak. Denial of service through memory exhaustion. This vulnerability was patched in versions(s) 1.26.3, 1.25.8, 1.24.9, 1.23.11.

Affected products

envoyproxy envoy: before 1.23.11; from 1.24.0 before 1.24.9; from 1.25.0 before 1.25.8; from 1.26.0 before 1.26.3 — fixed in 1.23.11, 1.24.9, 1.25.8, 1.26.3
nghttp2: before 1.55.1 — fixed in 1.55.1

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.23.11, 1.24.9, 1.25.8, 1.26.3; nghttp2 1.55.1. Check the vendor advisory for mitigations.

References

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