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Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length

Type: advisorySources: OSV

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, Envoy can translate a downstream HTTP/3 request that is complete at the transport layer (HEADERS with FIN / headers-only close) but still carries a nonzero Content-Length into a complete upstream HTTP/1 request with unresolved body debt. In an HTTP/1 upstream deployment where the origin replies before reading the declared body and keeps the connection reusable, the beginning of the next Envoy-generated upstream request can be consumed as the first request's body. The remaining bytes are then parsed by the origin as a new HTTP/1 request. This was reproduced as a route-bypass/desync: direct /pwn was denied by Envoy, but the second downstream H3 stream received the response for backend-parsed GET /pwn HTTP/1.1. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-48743
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 04:43 UTC · Revision 1

Source evidence

Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length

core-osv · Original source

Published 26 Jun 2026, 17:34 UTC

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, Envoy can translate a downstream HTTP/3 request that is complete at the transport layer (HEADERS with FIN / headers-only close) but still carries a nonzero Content-Length into a complete upstream HTTP/1 request with unresolved body debt. In an HTTP/1 upstream deployment where the origin replies before reading the declared body and keeps the connection reusable, the beginning of the next Envoy-generated upstream request can be consumed as the first request's body. The remaining bytes are then parsed by the origin as a new HTTP/1 request. This was reproduced as a route-bypass/desync: direct /pwn was denied by Envoy, but the second downstream H3 stream received the response for backend-parsed GET /pwn HTTP/1.1. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.

osv:CVE-2026-48743
Complete source record
{
  "id": "25c934bb3f44f1733d2a03a63e09a6f12a2669a80538aca8c48dbead93351419",
  "url": "https://osv.dev/vulnerability/CVE-2026-48743",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length",
    "summary": "Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, Envoy can translate a downstream HTTP/3 request that is complete at the transport layer (HEADERS with FIN / headers-only close) but still carries a nonzero Content-Length into a complete upstream HTTP/1 request with unresolved body debt. In an HTTP/1 upstream deployment where the origin replies before reading the declared body and keeps the connection reusable, the beginning of the next Envoy-generated upstream request can be consumed as the first request's body. The remaining bytes are then parsed by the origin as a new HTTP/1 request. This was reproduced as a route-bypass/desync: direct /pwn was denied by Envoy, but the second downstream H3 stream received the response for backend-parsed GET /pwn HTTP/1.1. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.",
    "evidence": "osv:CVE-2026-48743",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-48743",
      "aliases": [
        "BIT-envoy-2026-48743",
        "CVE-2026-48743",
        "GHSA-8phg-2h2q-jgxf"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/envoyproxy/envoy",
              "type": "GIT",
              "events": [
                {
                  "introduced": "84305a6cb64bd55aaf606bdd53de7cd6080427a1"
                },
                {
                  "fixed": "adb998f2875986005be294d10231a9c9a497e30d"
                },
                {
                  "introduced": "63ee0dc79dce88117c6bd2df5a742f8eb67ea980"
                },
                {
                  "fixed": "57198c441a298a75097c690726d90974549a9778"
                },
                {
                  "introduced": "6d9bb7d9a85d616b220d1f8fe67b61f82bbdb8d3"
                },
                {
                  "fixed": "f97695a50e11f5ff6719e129a466bf9204b64a7f"
                },
                {
                  "introduced": "f1dd21b16c244bda00edfb5ffce577e12d0d2ec2"
                },
                {
                  "fixed": "0ebfcfe5b0484b89ca85b761da9e05ce75dbda8d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.35.0"
                      },
                      {
                        "fixed": "1.35.13"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.36.0"
                      },
                      {
                        "fixed": "1.36.9"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.37.0"
                      },
                      {
                        "fixed": "1.37.5"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "1.38.0"
                      },
                      {
                        "fixed": "1.38.3"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.38.2",
            "v1.37.4",
            "v1.36.8",
            "v1.35.12",
            "v1.38.1",
            "v1.37.3",
            "v1.36.7",
            "v1.35.11",
            "v1.38.0",
            "v1.37.2",
            "v1.36.6",
            "v1.35.10",
            "v1.37.1",
            "v1.36.5",
            "v1.35.9",
            "v1.37.0",
            "v1.36.4",
            "v1.35.8",
            "v1.36.3",
            "v1.35.7",
            "v1.35.6",
            "v1.36.2",
            "v1.36.1",
            "v1.35.5",
            "v1.36.0",
            "v1.35.4",
            "v1.35.3",
            "v1.35.2",
            "v1.35.1",
            "v1.35.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-48743.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:25.680511306Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48743.json",
        "https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-48743"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-444"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/48xxx/CVE-2026-48743.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-48743",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 492512,
  "published_at": "2026-06-26T17:34:22.47+00:00"
}