{"id":"CVE-2026-73548","title":"Envoy is an open source edge and service proxy designed for cloud-native applications","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.…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","cwe":["CWE-444"],"vendor":"envoyproxy","product":"envoy","affected":["envoy < 1.36.10","envoy >= 1.37.0, < 1.37.6","envoy >= 1.38.0, < 1.38.4","envoy >= 1.39.0, < 1.39.1"],"published":"2026-09-21","updated":"2026-09-21","sourceUpdated":"2026-09-21T20:17:28.397","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-73548","references":[{"url":"https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.36.10","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.37.6","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.38.4","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/releases/tag/v1.39.1","label":"security-advisories@github.com"},{"url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2","label":"security-advisories@github.com"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-21T19:51:58.874Z","slug":"CVE-2026-73548","body":"## Overview\n\nEnvoy 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}