CVE-2026-73548 (GCVE-0-2026-73548)

Vulnerability from cvelistv5 – Published: 2026-09-21 19:35 – Updated: 2026-09-21 19:35
VLAI
Title
Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CWE
  • CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
Impacted products
Vendor Product Version CPE status
envoyproxy envoy Affected: < 1.36.10
Affected: >= 1.37.0, < 1.37.6
Affected: >= 1.38.0, < 1.38.4
Affected: >= 1.39.0, < 1.39.1
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "envoy",
          "vendor": "envoyproxy",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.36.10"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.37.0, \u003c 1.37.6"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.38.0, \u003c 1.38.4"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.39.0, \u003c 1.39.1"
            }
          ]
        }
      ],
      "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\u0027s 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."
        }
      ],
      "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",
              "description": "CWE-444: Inconsistent Interpretation of HTTP Requests (\u0027HTTP Request/Response Smuggling\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-21T19:35:15.275Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b",
          "tags": [
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          "url": "https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/releases/tag/v1.36.10",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.36.10"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/releases/tag/v1.37.6",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.37.6"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/releases/tag/v1.38.4",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.38.4"
        },
        {
          "name": "https://github.com/envoyproxy/envoy/releases/tag/v1.39.1",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.39.1"
        }
      ],
      "source": {
        "advisory": "GHSA-3vhp-c83q-jqc2",
        "discovery": "UNKNOWN"
      },
      "title": "Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy\u0027s shared backend pool"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-73548",
    "datePublished": "2026-09-21T19:35:15.275Z",
    "dateReserved": "2026-08-12T20:53:46.379Z",
    "dateUpdated": "2026-09-21T19:35:15.275Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "envoy",
                "vendor": "envoyproxy",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 1.36.10"
                  },
                  {
                    "status": "affected",
                    "version": "\u003e= 1.37.0, \u003c 1.37.6"
                  },
                  {
                    "status": "affected",
                    "version": "\u003e= 1.38.0, \u003c 1.38.4"
                  },
                  {
                    "status": "affected",
                    "version": "\u003e= 1.39.0, \u003c 1.39.1"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "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\u0027s 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",
        "lastModified": "2026-09-21T20:17:28.397",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "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"
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              "impactScore": 3.6,
              "source": "security-advisories@github.com",
              "type": "Secondary"
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            "url": "https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.36.10"
          },
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            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.37.6"
          },
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            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.38.4"
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            "source": "security-advisories@github.com",
            "url": "https://github.com/envoyproxy/envoy/releases/tag/v1.39.1"
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            "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2"
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        ],
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        "vulnStatus": "Received",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-444"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    }
  }
}



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