Reference page — cumulative record through Thursday, October 8, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-73548

CVE-2026-73548HIGH

envoyproxy envoy — Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  U  H  N  N    7.5   .0046   38.2     —

AFFECTED
  Product  Versions     Fixed
  envoy    < 1.36.10 –  —

TIMELINE
  Aug 12  Reserved by GitHub_M
  Sep 21  Published (CNA: GitHub_M)
  Oct 5   EXPLOIT PUBLISHED — CVE-2026-73548 (envoyproxy envoy). Public exploit reference added.

CWE-444 · CNA: GitHub_M · CVSS v3.1 · 9 references · NVD status: Analyzed

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 forwards data for a configured non-WebSocket HTTP upgrade before the upstream accepts the upgrade. An unauthenticated HTTP/2 client can place a complete HTTP/1.1 request in extended CONNECT data; Envoy downgrades the request, writes the data unframed to a keep-alive HTTP/1.1 upstream, and returns the socket to the shared pool while the smuggled response remains queued. A different downstream client can then receive the attacker's response. The relevant scope boundary is that webSocket upgrades, plain CONNECT, disabled backend keep-alive, per-downstream pools, and max_requests_per_connection set to 1 are not affected by the demonstrated path. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 12, 2026	Reserved	Reserved by GitHub_M
September 21, 2026	Published	Published (CNA: GitHub_M)
October 5, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-73548 (envoyproxy envoy). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
envoyproxy	envoy	—	< 1.36.10	—

Weaknesses

CWE-444

References (9)

https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361 [Patch]
https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b [Patch]
https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c [Patch]
https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766 [Patch]
https://github.com/envoyproxy/envoy/releases/tag/v1.36.10 [Release Notes]
https://github.com/envoyproxy/envoy/releases/tag/v1.37.6 [Release Notes]
https://github.com/envoyproxy/envoy/releases/tag/v1.38.4 [Release Notes]
https://github.com/envoyproxy/envoy/releases/tag/v1.39.1 [Release Notes]
https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 [Exploit, Vendor Advisory]

Authoritative record: CVE-2026-73548 at cve.org

Vendors: envoyproxy

Weaknesses: CWE-444

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-73548 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Thursday, October 8, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.