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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-73548
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-21 20:17:28 UTC
Updated2026-09-21 20:17:28 UTC
DescriptionEnvoy 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Problem Types: CWE-444 | CWE-444 CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Envoyproxy Envoy affected < 1.36.10 Not specified
CNA Envoyproxy Envoy affected >= 1.37.0, < 1.37.6 Not specified
CNA Envoyproxy Envoy affected >= 1.38.0, < 1.38.4 Not specified
CNA Envoyproxy Envoy affected >= 1.39.0, < 1.39.1 Not specified

References

ReferenceSourceLinkTags
github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c [email protected] github.com
github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766 [email protected] github.com
github.com/envoyproxy/envoy/releases/tag/v1.37.6 [email protected] github.com
github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 [email protected] github.com
github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361 [email protected] github.com
github.com/envoyproxy/envoy/releases/tag/v1.39.1 [email protected] github.com
github.com/envoyproxy/envoy/releases/tag/v1.36.10 [email protected] github.com
github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b [email protected] github.com
github.com/envoyproxy/envoy/releases/tag/v1.38.4 [email protected] github.com
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