{"id":"CVE-2026-123612","aliases":["DEBIAN-CVE-2026-123612","EUVD-2026-119371","GHSA-jrx3-hh25-gg3m","GHSA-vp88-798v-h67f","RUSTSEC-2026-0347","UBUNTU-CVE-2026-123612"],"status":"published","title":"rustls 0.23.44 and 0.23.45 ECH Rejection Application Data Disclosure","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","severity":{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.0011,"percentile":0.01266,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-200","CWE-696"],"published":"2026-10-14T12:00:00Z","modified":"2026-11-10T02:50:22Z","fixes":[{"ecosystem":"crates.io","package":"rustls","fixed_in":["0.23.46","0.24.0-dev.2"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"crates.io","package":"rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.23.44"},{"fixed":"0.23.46"}]}]},{"source":"ghsa","ecosystem":"crates.io","package":"rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.24.0-dev.1"},{"fixed":"0.24.0-dev.2"}]}]},{"source":"osv","ecosystem":"Debian:12","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.20.8-4","0.20.8-4.1","0.20.8-4.2","0.21.10-1","0.21.12-1","0.21.12-2","0.21.12-3","0.21.12-4","0.21.12-5","0.21.12-6","0.21.12-7","0.21.12-8","0.21.12-9","0.21.5-1","0.21.5-2","0.21.5-3","0.21.5-4","0.21.5-5","0.21.6-1","0.21.6-2","0.21.6-3","0.21.6-4","0.21.7-1","0.21.8-1","0.21.8-2","0.21.8-3","0.21.8-3.1","0.21.9-1","0.23.16-1","0.23.20+ds-1","0.23.20+ds-10","0.23.20+ds-2","0.23.20+ds-3","0.23.20+ds-4","0.23.20+ds-5","0.23.20+ds-6","0.23.20+ds-7","0.23.20+ds-8","0.23.20+ds-9","0.23.25+ds-1","0.23.26+ds-1","0.23.31+ds-1","0.23.31+ds-2","0.23.31+ds-3","0.23.31+ds-4","0.23.31+ds-5","0.23.31+ds-6","0.23.31+ds-7","0.23.32+ds-1","0.23.32+ds-2","0.23.33+ds-1","0.23.33+ds-2","0.23.33+ds-3","0.23.33+ds-4","0.23.35+ds-1","0.23.36+ds-1","0.23.37+ds-1","0.23.37+ds-2","0.23.37+ds-3","0.23.38+ds-1","0.23.40+ds-1","0.23.41+ds-1","0.23.43+ds-1","0.23.45+ds-1","0.23.46+ds-1"]},{"source":"osv","ecosystem":"Debian:13","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.23.26+ds-1","0.23.31+ds-1","0.23.31+ds-2","0.23.31+ds-3","0.23.31+ds-4","0.23.31+ds-5","0.23.31+ds-6","0.23.31+ds-7","0.23.32+ds-1","0.23.32+ds-2","0.23.33+ds-1","0.23.33+ds-2","0.23.33+ds-3","0.23.33+ds-4","0.23.35+ds-1","0.23.36+ds-1","0.23.37+ds-1","0.23.37+ds-2","0.23.37+ds-3","0.23.38+ds-1","0.23.40+ds-1","0.23.41+ds-1","0.23.43+ds-1","0.23.45+ds-1","0.23.46+ds-1"]},{"source":"osv","ecosystem":"Debian:14","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.23.26+ds-1","0.23.31+ds-1","0.23.31+ds-2","0.23.31+ds-3","0.23.31+ds-4","0.23.31+ds-5","0.23.31+ds-6","0.23.31+ds-7","0.23.32+ds-1","0.23.32+ds-2","0.23.33+ds-1","0.23.33+ds-2","0.23.33+ds-3","0.23.33+ds-4","0.23.35+ds-1","0.23.36+ds-1","0.23.37+ds-1","0.23.37+ds-2","0.23.37+ds-3","0.23.38+ds-1","0.23.40+ds-1","0.23.41+ds-1","0.23.43+ds-1","0.23.45+ds-1","0.23.46+ds-1"]},{"source":"osv","ecosystem":"crates.io","package":"rustls","ranges":[{"type":"SEMVER","events":[{"introduced":"0.23.44"},{"fixed":"0.23.46"}]}]},{"source":"osv","ecosystem":"crates.io","package":"rustls","ranges":[{"type":"SEMVER","events":[{"introduced":"0.24.0-dev.1"},{"fixed":"0.24.0-dev.2"}]}]},{"source":"osv","ecosystem":"crates.io","package":"rustls","ranges":[{"type":"SEMVER","events":[{"introduced":"0.23.44"},{"fixed":"0.23.46"}]}]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.21.6-3","0.21.7-1","0.21.9-1","0.21.10-1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.23.36+ds-1","0.23.41+ds-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"rust-rustls","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.23.26+ds-1","0.23.33+ds-3build2","0.23.35+ds-1","0.23.35+ds-1build1","0.23.36+ds-1"]}],"products":[{"vendor":"rustls","product":"rustls"},{"vendor":"rustls project","product":"rustls"}],"references":[{"url":"https://github.com/rustls/rustls/security/advisories/GHSA-vp88-798v-h67f","tags":["vendor-advisory","advisory","web","report"]},{"url":"https://www.vulncheck.com/advisories/rustls-0.23.44-and-0.23.45-ech-rejection-application-data-disclosure","tags":["third-party-advisory","advisory","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-123612","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-jrx3-hh25-gg3m"},{"url":"https://github.com/rustls/rustls/pull/3300","tags":["web","report"]},{"url":"https://github.com/rustls/rustls/pull/3354","tags":["web"]},{"url":"https://github.com/rustls/rustls/commit/2bd5c0cefabb2c5fd4100383a736d59f9671b9b4","tags":["web"]},{"url":"https://github.com/rustls/rustls/commit/4de14a508fbfa2273203ec17d9dfdd0fbd29e8d1","tags":["web"]},{"url":"https://github.com/rustls/rustls/commit/7dcbe4c1ae12185237d22e9197583329630a2014","tags":["web"]},{"url":"https://github.com/rustls/rustls/releases/tag/v/0.23.46","tags":["web"]},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0347.html","tags":["web","advisory","report"]},{"url":"https://github.com/advisories/GHSA-vp88-798v-h67f","tags":["report"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/123xxx/CVE-2026-123612.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-123612","tags":["advisory"]},{"url":"https://github.com/rustls/rustls","tags":["package"]},{"url":"https://crates.io/crates/rustls","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2026-123612","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-123612","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-123612","title":"rustls 0.23.44 and 0.23.45 ECH Rejection Application Data Disclosure","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T01:38:36.873Z","modified":"2026-11-12T13:40:04.848Z","cvss":[{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"medium","assessor":"cna"},{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"cna"}],"cwes":["CWE-696"],"updated_at":"2026-11-08T02:36:49.037074Z"}],"euvd":[{"id":"EUVD-2026-119371","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T01:38:36Z","modified":"2026-11-12T13:40:04Z","cvss":[{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"medium"}],"updated_at":"2026-11-08T06:12:04.155226Z"}],"ghsa":[{"id":"GHSA-jrx3-hh25-gg3m","title":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application...","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T03:30:37Z","modified":"2026-11-08T03:30:38Z","cvss":[{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"medium"},{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-696"],"updated_at":"2026-11-08T03:41:53.166172Z"},{"id":"GHSA-vp88-798v-h67f","title":"rustls: ECH rejection can expose buffered application data to authenticated outer server before `ech_required` alert","description":"In rustls 0.23.44 and 0.23.45, application data that a client buffers before the handshake completes is sent to the server even when the server rejects Encrypted Client Hello (ECH).\n\nWhen the server rejects ECH, the client completes the handshake with the outer ClientHello and authenticates the server against the ECH config's `public_name`. At the end of the handshake, `start_traffic()` encrypts and queues any plaintext buffered by `ClientConnection::writer()`. It does this *before* checking for `EchStatus::Rejected` and queueing the `ech_required` alert.\n\nThe application then receives `Error::PeerIncompatible(ServerRejectedEncryptedClientHello)`, as expected. However, the client is still expected to call `write_tls()` to send the fatal alert, and that call also sends the encrypted application data. The server decrypts the data and only then receives the alert.\n\nThe ordering bug is older than 0.23.44. Before 0.23.44, the client checked the server certificate against the inner server name rather than `public_name`, so a correctly configured server failed certificate verification first and no data was sent. 0.23.44 fixed that check, which makes the ordinary rejection path reachable.\n\n# Impact\n\nPlaintext meant for the inner server, the one named in the encrypted ClientHello, goes to the client-facing server identified by `public_name`. That server is properly authenticated, so this is not an attack by an unauthenticated party. However this violates [RFC 9849](https://www.rfc-editor.org/info/rfc9849), which says the following:\n\n- Section 6.1.6: if the handshake and authentication succeed after ECH rejection, the client \"MUST ... abort the connection with an \"ech_required\" alert **before sending any application data to the server.**\"\n- Section 6.1.7: the certificate is checked only against `public_name`, and the connection \"MUST NOT\" be reported as successful to the application. rustls does report failure correctly. The problem is only that data is sent before the alert.\n\nThis affects only clients that meet all of these conditions:\n\n- They use `EchMode::Enable`. GREASE ECH is not affected.\n- They write application data before the handshake completes.\n- They connect to a server that rejects their ECH config, for example because the config is stale. This is the same case where the server returns retry configs.\n\nThe usual client response to rejection is to retry with the server's retry configs. In that case, the data has already gone to the outer server.","status":"published","published":"2026-10-27T16:08:59Z","modified":"2026-10-27T16:09:02Z","cvss":[{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-200"],"updated_at":"2026-11-02T14:41:37.912288Z"}],"nvd":[{"id":"CVE-2026-123612","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T02:16:56.597Z","modified":"2026-11-12T21:30:23.87Z","cvss":[{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"medium","assessor":"secondary"},{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low","assessor":"secondary"}],"cwes":["CWE-696"],"updated_at":"2026-11-12T15:31:32.275584Z"}],"osv":[{"id":"CVE-2026-123612","title":"rustls 0.23.44 and 0.23.45 ECH Rejection Application Data Disclosure","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T01:38:36.873Z","modified":"2026-11-09T02:30:53.815306592Z","cvss":[{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-696"],"updated_at":"2026-11-09T03:16:44.651171Z"},{"id":"DEBIAN-CVE-2026-123612","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-08T02:16:56.597Z","modified":"2026-11-08T10:00:15.297764727Z","cvss":[{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"updated_at":"2026-11-08T10:03:28.621517Z"},{"id":"GHSA-vp88-798v-h67f","title":"rustls: ECH rejection can expose buffered application data to authenticated outer server before `ech_required` alert","description":"In rustls 0.23.44 and 0.23.45, application data that a client buffers before the handshake completes is sent to the server even when the server rejects Encrypted Client Hello (ECH).\n\nWhen the server rejects ECH, the client completes the handshake with the outer ClientHello and authenticates the server against the ECH config's `public_name`. At the end of the handshake, `start_traffic()` encrypts and queues any plaintext buffered by `ClientConnection::writer()`. It does this *before* checking for `EchStatus::Rejected` and queueing the `ech_required` alert.\n\nThe application then receives `Error::PeerIncompatible(ServerRejectedEncryptedClientHello)`, as expected. However, the client is still expected to call `write_tls()` to send the fatal alert, and that call also sends the encrypted application data. The server decrypts the data and only then receives the alert.\n\nThe ordering bug is older than 0.23.44. Before 0.23.44, the client checked the server certificate against the inner server name rather than `public_name`, so a correctly configured server failed certificate verification first and no data was sent. 0.23.44 fixed that check, which makes the ordinary rejection path reachable.\n\n# Impact\n\nPlaintext meant for the inner server, the one named in the encrypted ClientHello, goes to the client-facing server identified by `public_name`. That server is properly authenticated, so this is not an attack by an unauthenticated party. However this violates [RFC 9849](https://www.rfc-editor.org/info/rfc9849), which says the following:\n\n- Section 6.1.6: if the handshake and authentication succeed after ECH rejection, the client \"MUST ... abort the connection with an \"ech_required\" alert **before sending any application data to the server.**\"\n- Section 6.1.7: the certificate is checked only against `public_name`, and the connection \"MUST NOT\" be reported as successful to the application. rustls does report failure correctly. The problem is only that data is sent before the alert.\n\nThis affects only clients that meet all of these conditions:\n\n- They use `EchMode::Enable`. GREASE ECH is not affected.\n- They write application data before the handshake completes.\n- They connect to a server that rejects their ECH config, for example because the config is stale. This is the same case where the server returns retry configs.\n\nThe usual client response to rejection is to retry with the server's retry configs. In that case, the data has already gone to the outer server.","status":"published","published":"2026-10-27T16:08:59Z","modified":"2026-11-08T10:55:39.094187294Z","cvss":[{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"cwes":["CWE-200"],"updated_at":"2026-11-08T11:04:05.022583Z"},{"id":"RUSTSEC-2026-0347","title":"Buffered application data sent to outer server after ECH rejection","description":"When a server rejects Encrypted Client Hello (ECH), the client completes the\nhandshake using the outer ClientHello and authenticates the server against the\nECH config's `public_name`. At the end of that handshake, rustls encrypted and\nqueued any application data buffered via `ClientConnection::writer()` *before*\nqueueing the `ech_required` alert.\n\nThe application correctly receives\n`Error::PeerIncompatible(ServerRejectedEncryptedClientHello)`, but the next\n`write_tls()` call (needed to send the alert) also sends the buffered\napplication data. Plaintext meant for the inner server therefore goes to the\nclient-facing server named by `public_name`.\n\nThat server is authenticated, so this is not exploitable by an unauthenticated\nparty, but it violates RFC 9849 section 6.1.6, which requires the client to\nabort with `ech_required` \"before sending any application data to the server\".\n\nThis affects only clients that:\n\n- use `EchMode::Enable` (GREASE ECH is not affected),\n- write application data before the handshake completes, and\n- connect to a server that rejects their ECH config (for example, because it is stale).\n\nThe underlying ordering bug is older, but before 0.23.44 the client checked\nthe server certificate against the inner server name rather than `public_name`,\nso certificate verification failed first and no data was sent.","status":"published","published":"2026-10-14T12:00:00Z","modified":"2026-11-09T09:21:20Z","cvss":[{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"}],"updated_at":"2026-11-08T11:04:05.022583Z"},{"id":"UBUNTU-CVE-2026-123612","description":"rustls 0.23.44 and 0.23.45 contain an information disclosure vulnerability that sends application data buffered before the handshake completes to the client-facing server when Encrypted Client Hello is rejected. Because start_traffic() queues plaintext from ClientConnection::writer() before sending the ech_required alert, the authenticated public_name server receives data intended for the inner server.","status":"published","published":"2026-11-09T00:00:00Z","modified":"2026-11-10T02:50:22.400300548Z","cvss":[{"version":"3.1","score":2.3,"vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","level":"low"},{"version":"4.0","score":4.6,"vector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","level":"medium"}],"updated_at":"2026-11-10T03:18:58.105788Z"}]}}