CVE-2026-73550

7.5 HIGHpublic exploit available

Published 2026-09-21 · Updated 2026-09-21

AI risk analysis

Summary: The flaw allows unauthenticated clients to exploit HPACK indexing to submit large Host values, causing out-of-memory issues in Envoy proxies.
Exploitability: Exploitation requires sending multiple HTTP/2 streams with large Host headers; preconditions include the use of affected Envoy versions prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1.
Blast radius: If exploited, it could lead to Denial of Service (DoS) by overwhelming the proxy with excessive memory usage.
Prioritized remediation: Upgrade Envoy to version 1.36.10 or later.

doshttp2proxymemory

Analysis generated locally by qwen2.5:7b-instruct (no data left the box). AI-assisted — verify against primary sources before acting.

NVD description

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weaknesses

CWE-401

Public exploit & PoC references

All references

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

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