CVE-2026-73548: 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…

PriorityP347high7.5CVSS 3.1

AVNACLPRNUINSUCHINAN

EPSS

0.46%

39.3th percentile

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.

Affected

8 ranges

Vendor	Product	Version range	Fixed in
envoyproxy	envoy	< 1.36.10	1.36.10
envoyproxy	envoy	—	—
envoyproxy	envoy	—	—
envoyproxy	envoy	—	—
envoyproxy	envoy	>= 1.37.0 < 1.37.6	1.37.6
envoyproxy	envoy	>= 1.38.0 < 1.38.4	1.38.4
envoyproxy	envoy	>= 1.39.0 < 1.39.1	1.39.1
openshift-service-mesh	istio-proxyv2-rhel9	—	—

CVSS provenance

nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

vendor_redhat7.5HIGH

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