Vulnerability details

CVE-2026-73548

envoyproxy envoy

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

CVSS 3.1

7.5High

Official 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.

CVSS scores

Score	Version	Source	Vector
7.5High	3.1	CVEProject cvelistV5 (CNA) (GitHub_M)	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`

Affected products

Vendor	Product	Versions	Source
envoyproxy	envoy	< 1.36.10	CVEProject cvelistV5 (CNA)
envoyproxy	envoy	>= 1.37.0, < 1.37.6	CVEProject cvelistV5 (CNA)
envoyproxy	envoy	>= 1.38.0, < 1.38.4	CVEProject cvelistV5 (CNA)
envoyproxy	envoy	>= 1.39.0, < 1.39.1	CVEProject cvelistV5 (CNA)

References and advisories

https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361 x_refsource_MISC
https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b x_refsource_MISC
https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c x_refsource_MISC
https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766 x_refsource_MISC
https://github.com/envoyproxy/envoy/releases/tag/v1.36.10 x_refsource_MISC
https://github.com/envoyproxy/envoy/releases/tag/v1.37.6 x_refsource_MISC
https://github.com/envoyproxy/envoy/releases/tag/v1.38.4 x_refsource_MISC
https://github.com/envoyproxy/envoy/releases/tag/v1.39.1 x_refsource_MISC
https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 x_refsource_CONFIRM

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Details

Published: 2026-09-21
Last updated: 2026-09-25
State: Published
Assigner (CNA): GitHub_M

Exploit prediction (EPSS)

0.46%

Probability of exploitation in 30 days

40.5%

Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable: Yes
Exploitation: Proof of concept
Technical impact: Partial

Weaknesses (CWE)

CWE-444
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')