---
id: CVE-2026-73550
title: >-
  Envoy is an open source edge and service proxy designed for cloud-native
  applications
summary: >-
  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 copies every
  decoded HTTP/2 Host header value before discarding it when :authority is
  already pres…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-401
vendor: envoyproxy
product: envoy
affected:
  - envoy < 1.36.10
  - 'envoy >= 1.37.0, < 1.37.6'
  - 'envoy >= 1.38.0, < 1.38.4'
  - 'envoy >= 1.39.0, < 1.39.1'
published: '2026-09-21'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T18:12:04.247'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-73550'
references:
  - url: >-
      https://github.com/envoyproxy/envoy/commit/0910997f70e91d2d20c329bb507bfce44ce01f80
    label: security-advisories@github.com
  - url: >-
      https://github.com/envoyproxy/envoy/commit/1fec994c868df008cdd4ae285aab58a196fd31f2
    label: security-advisories@github.com
  - url: >-
      https://github.com/envoyproxy/envoy/commit/3fd0ffee7ac87adf3bc6e421656bb96310512300
    label: security-advisories@github.com
  - url: >-
      https://github.com/envoyproxy/envoy/commit/fc75d8e35b0d11acbae18b63a0bd96e32e84f61b
    label: security-advisories@github.com
  - url: 'https://github.com/envoyproxy/envoy/releases/tag/v1.36.10'
    label: security-advisories@github.com
  - url: 'https://github.com/envoyproxy/envoy/releases/tag/v1.37.6'
    label: security-advisories@github.com
  - url: 'https://github.com/envoyproxy/envoy/releases/tag/v1.38.4'
    label: security-advisories@github.com
  - url: 'https://github.com/envoyproxy/envoy/releases/tag/v1.39.1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/envoyproxy/envoy/security/advisories/GHSA-qgf6-qvhw-4hvh
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
epss: 0.00879
epssPercentile: 0.57309
ingestedAt: '2026-09-21T19:51:58.866Z'
---

## Overview

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 copies every decoded HTTP/2 Host header value before discarding it when :authority is already present. The discarded value bypasses saveHeader, so its bytes and count are not charged against request header limits. An unauthenticated client can use HPACK indexing to submit many references to a large Host value across a bounded number of streams, forcing extreme header-copy allocation and causing the proxy to be out-of-memory killed. The relevant scope boundary is that the demonstrated amplification uses HTTP/2 HPACK and the duplicate Host discard behavior. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.