{"id":"CVE-2025-64763","aliases":["BIT-envoy-2025-64763","EUVD-2025-201099","GHSA-rj35-4m94-77jh"],"status":"published","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","severity":{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00323,"percentile":0.2567,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-693"],"published":"2025-12-03T18:13:58Z","modified":"2026-10-28T02:30:43Z","fixes":[{"ecosystem":"Go","package":"github.com/envoyproxy/envoy","fixed_in":["1.36.3","1.35.7","1.34.11","1.33.13"],"sources":["ghsa","osv"]},{"ecosystem":"Bitnami","package":"envoy","fixed_in":["1.33.13","1.34.11","1.35.7","1.36.3"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.36.0"},{"last_affected":"1.36.2"},{"fixed":"1.36.3"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.35.0"},{"last_affected":"1.35.6"},{"fixed":"1.35.7"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.34.0"},{"last_affected":"1.34.10"},{"fixed":"1.34.11"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"1.33.12"},{"fixed":"1.33.13"}]}]},{"source":"osv","ecosystem":"Bitnami","package":"envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.33.13"},{"introduced":"1.34.0"},{"fixed":"1.34.11"},{"introduced":"1.35.0"},{"fixed":"1.35.7"},{"introduced":"1.36.0"},{"fixed":"1.36.3"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.36.0"},{"fixed":"1.36.3"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.35.0"},{"fixed":"1.35.7"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.34.0"},{"fixed":"1.34.11"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.33.13"}]}]}],"products":[{"vendor":"envoyproxy","product":"envoy"}],"references":[{"url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-rj35-4m94-77jh","tags":["x_refsource_CONFIRM","Patch","Vendor Advisory","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-64763","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-rj35-4m94-77jh"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/64xxx/CVE-2025-64763.json","tags":["advisory"]},{"url":"https://github.com/envoyproxy/envoy","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2025-64763","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","status":"published","published":"2025-12-03T18:13:58.496Z","modified":"2025-12-03T20:02:40.284Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"cna"}],"cwes":["CWE-693"],"updated_at":"2026-11-02T14:32:46.750177Z"}],"euvd":[{"id":"EUVD-2025-201099","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","status":"published","published":"2025-12-03T18:13:58Z","modified":"2025-12-03T20:02:40Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"updated_at":"2026-11-02T19:49:10.321316Z"}],"ghsa":[{"id":"GHSA-rj35-4m94-77jh","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"## Summary\n\nForwarding of early CONNECT data in TCP proxy mode.\n\n## Details\n\nPer [RFC 7231-4.3.6](https://www.rfc-editor.org/rfc/rfc7231#section-4.3.6) the sender of CONNECT (and all inbound proxies)  switch to tunnel mode only after receiving 2xx response. However in TCP proxy mode, Envoy accepts client data before it has issued a 2xx response and eagerly proxies it to an established TCP connection. This creates possibility of a de-synchronized tunnel state if a proxy upstream from Envoy responds with a status other an 2xx.\n\nThe RFC does not specify the behavior in case an early CONNECT data is received and early CONNECT data is common as a latency reduction mechanism. To prevent disruption to existing deployments Envoy will by default allow early CONNECT data. Setting the `envoy.reloadable_features.reject_early_connect_data` runtime flag to `true` will cause CONNECT requests that send data before 2xx response to be rejected. This options should be enabled if there are intermediaries upstream from Envoy that may reject establishment of a CONNECT tunnel. \n\n## Impact\n\nDe-synchronization of CONNECT tunnel state if a forwarding proxy upstream from Envoy responds with a non 2xx status.\n\n## Attack vector(s)\nSending data for a CONNECT request before receiving 2xx response.\n\n## Patches\nUsers should upgrade to v1.36.3, v1.35.7, v1.34.11 or v1.33.13\n\n## Credits\n\n[chasingimpact](https://github.com/chasingimpact) (Patrick)","status":"published","published":"2025-12-05T18:12:51Z","modified":"2025-12-10T20:48:24Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-693"],"updated_at":"2026-11-02T14:39:12.222121Z"}],"nvd":[{"id":"CVE-2025-64763","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","status":"published","published":"2025-12-03T18:15:47.037Z","modified":"2026-06-17T09:55:10.24Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"secondary"},{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-693"],"updated_at":"2026-11-02T14:11:47.746175Z"}],"osv":[{"id":"CVE-2025-64763","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","status":"published","published":"2025-12-03T18:13:58.496Z","modified":"2026-10-28T02:30:43.541298992Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-693"],"updated_at":"2026-11-02T15:44:51.851511Z"},{"id":"GHSA-rj35-4m94-77jh","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"## Summary\n\nForwarding of early CONNECT data in TCP proxy mode.\n\n## Details\n\nPer [RFC 7231-4.3.6](https://www.rfc-editor.org/rfc/rfc7231#section-4.3.6) the sender of CONNECT (and all inbound proxies)  switch to tunnel mode only after receiving 2xx response. However in TCP proxy mode, Envoy accepts client data before it has issued a 2xx response and eagerly proxies it to an established TCP connection. This creates possibility of a de-synchronized tunnel state if a proxy upstream from Envoy responds with a status other an 2xx.\n\nThe RFC does not specify the behavior in case an early CONNECT data is received and early CONNECT data is common as a latency reduction mechanism. To prevent disruption to existing deployments Envoy will by default allow early CONNECT data. Setting the `envoy.reloadable_features.reject_early_connect_data` runtime flag to `true` will cause CONNECT requests that send data before 2xx response to be rejected. This options should be enabled if there are intermediaries upstream from Envoy that may reject establishment of a CONNECT tunnel. \n\n## Impact\n\nDe-synchronization of CONNECT tunnel state if a forwarding proxy upstream from Envoy responds with a non 2xx status.\n\n## Attack vector(s)\nSending data for a CONNECT request before receiving 2xx response.\n\n## Patches\nUsers should upgrade to v1.36.3, v1.35.7, v1.34.11 or v1.33.13\n\n## Credits\n\n[chasingimpact](https://github.com/chasingimpact) (Patrick)","status":"published","published":"2025-12-05T18:12:51Z","modified":"2025-12-10T20:19:27.162055Z","cvss":[{"version":"3.1","score":3.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-693"],"updated_at":"2026-11-02T15:46:55.877614Z"},{"id":"BIT-envoy-2025-64763","title":"Envoy forwards early CONNECT data in TCP proxy mode","description":"Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.","status":"published","published":"2025-12-06T11:38:19.488Z","modified":"2026-09-08T08:47:31.822984351Z","updated_at":"2026-11-02T15:28:29.563843Z"}]}}