{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "1.36.10"
              },
              {
                "introduced": "1.37.0"
              },
              {
                "fixed": "1.37.6"
              },
              {
                "introduced": "1.38.0"
              },
              {
                "fixed": "1.38.4"
              },
              {
                "introduced": "1.39.0"
              },
              {
                "fixed": "1.39.1"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "introduced": "6d9bb7d9a85d616b220d1f8fe67b61f82bbdb8d3"
            },
            {
              "introduced": "f1dd21b16c244bda00edfb5ffce577e12d0d2ec2"
            },
            {
              "introduced": "8eea3285d6bdb89f8ea34632cfe7ce1608a8f374"
            },
            {
              "fixed": "053a8989382dd91542ecf0cef8f379b9cb761cdd"
            },
            {
              "fixed": "cf413bdb37b36d3ffbe570b8a48760abe2b588f5"
            },
            {
              "fixed": "ef2d997c1b022cf8b849a1d3521fbf234d79ca26"
            },
            {
              "fixed": "b579d07d3ad7ee11d32b105e91a5a39ad24718d7"
            },
            {
              "fixed": "309855626966cff176155c821043ed3b44671361"
            },
            {
              "fixed": "3c7998545a9c9fb3933a4bc1907d92f0e752bc2b"
            },
            {
              "fixed": "4633b8cce3d15b8734eefe232e30c12b0140b91c"
            },
            {
              "fixed": "bd6711f2617658e28dfa3df3dace6bfe3cfc0766"
            }
          ],
          "repo": "https://github.com/envoyproxy/envoy",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-3vhp-c83q-jqc2"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-444"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73548.json"
  },
  "details": "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.",
  "id": "CVE-2026-73548",
  "modified": "2026-09-26T03:30:51.113508086Z",
  "published": "2026-09-21T19:35:15.275Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.36.10"
    },
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.37.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.38.4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.39.1"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73548.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-73548"
    },
    {
      "type": "FIX",
      "url": "https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361"
    },
    {
      "type": "FIX",
      "url": "https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b"
    },
    {
      "type": "FIX",
      "url": "https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c"
    },
    {
      "type": "FIX",
      "url": "https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool"
}