{"id":"BIT-envoy-2026-73548","summary":"Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool","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.","aliases":["CVE-2026-73548","GHSA-3vhp-c83q-jqc2"],"modified":"2026-09-29T10:10:55.484820447Z","published":"2026-09-29T08:43:12.086Z","database_specific":{"severity":"High","cpes":["cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*"]},"references":[{"type":"WEB","url":"https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361"},{"type":"WEB","url":"https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2b"},{"type":"WEB","url":"https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91c"},{"type":"WEB","url":"https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766"},{"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":"WEB","url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73548"}],"affected":[{"package":{"name":"envoy","ecosystem":"Bitnami","purl":"pkg:bitnami/envoy"},"ranges":[{"type":"SEMVER","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"}]}],"database_specific":{"source":"https://github.com/bitnami/vulndb/tree/main/data/envoy/BIT-envoy-2026-73548.json"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"}]}],"schema_version":"1.9.0"}