Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length_CVE-2026-48743

{
    "lastseen": "",
    "description": "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.",
    "published": "2026-06-26T17:34:22.470Z",
    "modified": "2026-06-26T17:34:22.470Z",
    "type": "cve",
    "title": "Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length",
    "source": "GitHub_M",
    "references": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-8phg-2h2q-jgxf",
    "id": "CVE-2026-48743",
    "bulletinFamily": "",
    "cwe": [
        "CWE-444"
    ],
    "cvelist": null,
    "sourceData": "envoyproxy envoy >= 1.38.0, < 1.38.1\nenvoyproxy envoy >= 1.37.0, < 1.37.3\nenvoyproxy envoy >= 1.36.0, < 1.36.7\nenvoyproxy envoy >= 1.35.0, < 1.35.11",
    "sourceHref": "",
    "cvss": {
        "score": 7.5,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N",
        "version": "3.1"
    },
    "cvss2": [],
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        "baseScore": 0,
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        "confidentialityImpact": "",
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        "cvssV3": {
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "envoy",
    "version": ">= 1.38.0, < 1.38.1",
    "vendor": "envoyproxy",
    "ai_description": "",
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    "ai_score": 0
}