{"id":"GHSA-vp88-798v-h67f","revision":null,"records":[{"revision":"9f329331242a474a82b95f3756924bb0","observedAt":"2026-10-27T16:45:46.193+00:00","statement":{"source":"osv","id":"GHSA-vp88-798v-h67f","aliases":["RUSTSEC-2026-0347"],"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.","state":0,"publishedAt":"2026-10-27T16:08:59+00:00","modifiedAt":"2026-10-27T16:15:05.3366852+00:00","affected":[{"ecosystem":"crates.io","name":"rustls","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.23.44"},{"kind":"fixed","version":"0.23.46"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"crates.io","name":"rustls","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.24.0-dev.1"},{"kind":"fixed","version":"0.24.0-dev.2"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"LOW"}],"references":["https://github.com/rustls/rustls/security/advisories/GHSA-vp88-798v-h67f","https://github.com/rustls/rustls/pull/3300","https://github.com/rustls/rustls/pull/3354","https://github.com/rustls/rustls/commit/2bd5c0cefabb2c5fd4100383a736d59f9671b9b4","https://github.com/rustls/rustls/commit/4de14a508fbfa2273203ec17d9dfdd0fbd29e8d1","https://github.com/rustls/rustls/commit/7dcbe4c1ae12185237d22e9197583329630a2014","https://github.com/rustls/rustls","https://github.com/rustls/rustls/releases/tag/v/0.23.46","https://rustsec.org/advisories/RUSTSEC-2026-0347.html"],"sourceUrl":"https://github.com/advisories/GHSA-vp88-798v-h67f","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-vp88-798v-h67f","identifiers":["GHSA-vp88-798v-h67f","RUSTSEC-2026-0347"]},"retained":false,"historicalAffected":[]},{"revision":"c15f5e526b894ea593384e701c38f053","observedAt":"2026-10-24T13:19:54.901+00:00","statement":{"source":"osv","id":"RUSTSEC-2026-0347","aliases":["GHSA-vp88-798v-h67f"],"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.","state":0,"publishedAt":"2026-10-14T12:00:00+00:00","modifiedAt":"2026-10-14T13:30:02.4721034+00:00","affected":[{"ecosystem":"crates.io","name":"rustls","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0.23.44"},{"kind":"fixed","version":"0.23.46"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N","score":null,"severity":null}],"references":["https://crates.io/crates/rustls","https://rustsec.org/advisories/RUSTSEC-2026-0347.html","https://github.com/rustls/rustls/pull/3300"],"sourceUrl":"https://osv.dev/vulnerability/RUSTSEC-2026-0347","license":"OSV · upstream source license applies","key":"osv:RUSTSEC-2026-0347","identifiers":["RUSTSEC-2026-0347","GHSA-vp88-798v-h67f"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. Missing entries do not establish absence of exploitation.","generation":"2026-10-30T14:45:26.6987549+00:00","complete":true,"records":1764,"lastAttemptAt":"2026-10-30T14:45:26.6987549+00:00","lastSuccessAt":"2026-10-30T14:45:26.9497648+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.9497653+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"cve-program","scope":"Official CVE Program baseline and cumulative hourly delta; all vendors, published and rejected records","generation":"cve-7e2c4e7288f2c464ad8c61f3bb6017374714faedcc781283ac06a706ee1a820b-9ae73af7991357f8171c14345365990a8a2ca2ac30d2f5c0345295ca47cd8b59","complete":true,"records":417062,"lastAttemptAt":"2026-10-30T14:45:26.2761545+00:00","lastSuccessAt":"2026-10-30T13:45:42.363036+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.2761545+00:00","snapshotPublishedAt":"2026-10-30T13:19:40+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"euvd","scope":"Rolling EUVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global EUVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-2061c7564831481480eca7336a6a2d59","complete":false,"records":13525,"lastAttemptAt":"2026-10-30T14:57:22.1548673+00:00","lastSuccessAt":"2026-10-30T14:57:22.151+00:00","error":"74 identifier lookups failed; latest failures include HTTP 403. Other identifiers were checked independently.","lastVerifiedAt":"2026-10-30T14:57:22.151+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":12100,"expectedIdentifiers":13603,"failedIdentifiers":74},{"source":"first-epss:nuget","scope":"FIRST EPSS for explicit CVE aliases in the collected public NuGet archive. Not a global EPSS backfill.","generation":"2026-10-30T14:45:26.6987549+00:00","complete":true,"records":1094,"lastAttemptAt":"2026-10-30T14:45:26.6987549+00:00","lastSuccessAt":"2026-10-30T14:45:26.9516817+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.951682+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"nvd","scope":"Rolling NVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global NVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-6a13c6f8f39a448a8b96c895e97b0fc8","complete":true,"records":13543,"lastAttemptAt":"2026-10-30T14:45:34.6994115+00:00","lastSuccessAt":"2026-10-30T14:45:34.696+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:34.696+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13603,"expectedIdentifiers":13603,"failedIdentifiers":0},{"source":"osv:Go","scope":"Complete OSV Go ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"go-b597efeb8fc540d31a792e2148f8b153f027cb0902f6eec1f988f717bba80dd6","complete":true,"records":9806,"lastAttemptAt":"2026-10-30T14:45:26.6211704+00:00","lastSuccessAt":"2026-10-30T11:49:32.1566+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.6211704+00:00","snapshotPublishedAt":"2026-10-30T11:03:04+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:NuGet","scope":"Complete OSV NuGet ecosystem archive, including GitHub Advisory Database records; NuGet version matching only","generation":"nuget-2de9ccc5290f060c7aa63f89c25dd76f655a64ba1aba7c05c97fa3bee4f09899","complete":true,"records":1967,"lastAttemptAt":"2026-10-30T14:45:26.3367706+00:00","lastSuccessAt":"2026-10-28T20:55:34.2982937+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.3367706+00:00","snapshotPublishedAt":"2026-10-28T20:03:08+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:crates.io","scope":"Complete OSV crates.io ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"crates.io-f63fa91e750071ae88c9f82019ecd6c982fa4fcc1d3dc5ceb5d9c642fb6bf05c","complete":true,"records":3023,"lastAttemptAt":"2026-10-30T14:45:26.6363468+00:00","lastSuccessAt":"2026-10-30T11:49:36.4759887+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.6363468+00:00","snapshotPublishedAt":"2026-10-30T11:18:14+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:npm","scope":"Complete OSV npm ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"npm-38769c8a86ea1c9a6224e5523e119bd23337098bd8f535cc5952f8ec88cdd622","complete":true,"records":230950,"lastAttemptAt":"2026-10-30T14:45:26.5064351+00:00","lastSuccessAt":"2026-10-30T13:47:22.3495471+00:00","error":null,"lastVerifiedAt":"2026-10-30T14:45:26.5064351+00:00","snapshotPublishedAt":"2026-10-30T13:33:12+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null}]}