{"schemaVersion":3,"id":"CVE-2026-73548","aliases":[],"status":"published","duplicateOf":null,"title":null,"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.","dates":{"published":"2026-09-21T19:35:15.275Z","modified":"2026-09-24T22:35:14.446Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":7.5,"severity":"high","version":"3.1","versionLabel":"v3.1","source":"CVE.org","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":7.5,"severity":"high","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":7.5,"severity":"high","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00465,"percentile":0.39195,"severity":"low","asOf":"2026-10-21T00:00:00.000Z","change":{"pp":null,"baselineDate":null,"baselineScore":null},"history":[{"date":"2026-09-22T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-21T00:00:00.000Z","score":0.00465,"percentile":0.39195}],"last30":[{"date":"2026-09-22T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00665,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.0048,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00465,"percentile":null},{"date":"2026-10-20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