{"id":"CVE-2026-73548","state":"PUBLISHED","title":"Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool","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.","publishedAt":"2026-09-21T19:35:15.275Z","updatedAt":"2026-09-24T22:35:14.446Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["envoyproxy envoy"],"affected":[{"vendor":"envoyproxy","product":"envoy","versions":[{"version":"< 1.36.10","status":"affected"},{"version":">= 1.37.0, < 1.37.6","status":"affected"},{"version":">= 1.38.0, < 1.38.4","status":"affected"},{"version":">= 1.39.0, < 1.39.1","status":"affected"}]}],"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"],"weaknesses":["CWE-444"],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/73xxx/CVE-2026-73548.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-73548","state":"PUBLISHED","datePublished":"2026-09-21T19:35:15.275Z","dateUpdated":"2026-09-24T22:35:14.446Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-08-12T20:53:46.379Z"},"containers":{"cna":{"title":"Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool","descriptions":[{"lang":"en","value":"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":[{"vendor":"envoyproxy","product":"envoy","versions":[{"version":"< 1.36.10","status":"affected"},{"version":">= 1.37.0, < 1.37.6","status":"affected"},{"version":">= 1.38.0, < 1.38.4","status":"affected"},{"version":">= 1.39.0, < 1.39.1","status":"affected"}]}],"references":[{"url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2","name":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361","name":"https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b","name":"https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c","name":"https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766","name":"https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.36.10","name":"https://github.com/envoyproxy/envoy/releases/tag/v1.36.10","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.37.6","name":"https://github.com/envoyproxy/envoy/releases/tag/v1.37.6","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.38.4","name":"https://github.com/envoyproxy/envoy/releases/tag/v1.38.4","tags":["x_refsource_MISC"]},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.39.1","name":"https://github.com/envoyproxy/envoy/releases/tag/v1.39.1","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-444","lang":"en","description":"CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-09-21T19:35:15.275Z"},"source":{"advisory":"GHSA-3vhp-c83q-jqc2","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-24T22:34:49.061262Z","id":"CVE-2026-73548","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-24T22:35:14.446Z"}}]}}}