CVE-2026-73548

Severity CVSS v4.0:

Pending analysis

Type:

Unavailable / Other

Publication date:

21/09/2026

Last modified:

05/10/2026

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&#39;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.

Impact

Vector 3.x

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N CVSS v3.1 Severity and Metrics:

Base Score: 7.50 HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): High
Integrity (I): None
Availability (A): None

Base Score 3.x

7.50

Severity 3.x

HIGH

Vulnerable products and versions

CPE	From	Up to
cpe:2.3:a:envoyproxy:envoy::::::::		1.36.10 (excluding)
cpe:2.3:a:envoyproxy:envoy::::::::	1.37.0 (including)	1.37.6 (excluding)
cpe:2.3:a:envoyproxy:envoy::::::::	1.38.0 (including)	1.38.4 (excluding)
cpe:2.3:a:envoyproxy:envoy::::::::	1.39.0 (including)	1.39.1 (excluding)

To consult the complete list of CPE names with products and versions, see this page

CVE-2026-73548

Description

Impact

Vulnerable products and versions

References to Advisories, Solutions, and Tools