CVE-2026-73548
Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool
- State
- Published
- Severity
- 7.5 High
- Published
- Sep 21, 2026
- Updated
- Sep 24, 2026
- Reserved
- Aug 12, 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'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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N | GitHub_M |
Weaknesses
- CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected Products
| Product | Versions |
|---|---|
envoyenvoyproxy |
|
References
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2
- https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361
- https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b
- https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c
- https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766
- https://github.com/envoyproxy/envoy/releases/tag/v1.36.10
- https://github.com/envoyproxy/envoy/releases/tag/v1.37.6
- https://github.com/envoyproxy/envoy/releases/tag/v1.38.4
- https://github.com/envoyproxy/envoy/releases/tag/v1.39.1
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