{"id":"CVE-2021-32640","aliases":["GHSA-6fc8-4gx4-v693"],"url":"https://o3.security/vulnerability/CVE-2021-32640","summary":"ReDoS in Sec-Websocket-Protocol header","details":"### Impact\n\nA specially crafted value of the `Sec-Websocket-Protocol` header can be used to significantly slow down a ws server.\n\n### Proof of concept\n\n```js\nfor (const length of [1000, 2000, 4000, 8000, 16000, 32000]) {\n  const value = 'b' + ' '.repeat(length) + 'x';\n  const start = process.hrtime.bigint();\n\n  value.trim().split(/ *, */);\n\n  const end = process.hrtime.bigint();\n\n  console.log('length = %d, time = %f ns', length, end - start);\n}\n```\n\n### Patches\n\nThe vulnerability was fixed in ws@7.4.6 (https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff) and backported to ws@6.2.2 (https://github.com/websockets/ws/commit/78c676d2a1acefbc05292e9f7ea0a9457704bf1b) and ws@5.2.3 (https://github.com/websockets/ws/commit/76d47c1479002022a3e4357b3c9f0e23a68d4cd2).\n\n### Workarounds\n\nIn vulnerable versions of ws, the issue can be mitigated by reducing the maximum allowed length of the request headers using the [`--max-http-header-size=size`](https://nodejs.org/api/cli.html#cli_max_http_header_size_size) and/or the [`maxHeaderSize`](https://nodejs.org/api/http.html#http_http_createserver_options_requestlistener) options.\n\n### Credits\n\nThe vulnerability was responsibly disclosed along with a fix in private by [Robert McLaughlin](https://github.com/robmcl4) from University of California, Santa Barbara.\n","published":"2021-05-25T19:15:07.767Z","modified":"2026-07-09T12:20:09.027755Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.02821,"percentile":0.85872,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":1,"affectedPackages":[{"ecosystem":"npm","name":"ws","fixedVersion":"7.4.6"},{"ecosystem":"npm","name":"ws","fixedVersion":"6.2.2"},{"ecosystem":"npm","name":"ws","fixedVersion":"5.2.3"}],"fix":{"url":"https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff","label":"websockets/ws@00c425e"},"references":[{"type":"WEB","url":"https://lists.apache.org/thread.html/rdfa7b6253c4d6271e31566ecd5f30b7ce1b8fb2c89d52b8c4e0f4e30%40%3Ccommits.tinkerpop.apache.org%3E"},{"type":"ADVISORY","url":"https://security.netapp.com/advisory/ntap-20210706-0005/"},{"type":"FIX","url":"https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff"},{"type":"FIX","url":"https://github.com/websockets/ws/security/advisories/GHSA-6fc8-4gx4-v693"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-32640"},{"type":"WEB","url":"https://github.com/websockets/ws/issues/1895"},{"type":"PACKAGE","url":"https://github.com/websockets/ws"},{"type":"WEB","url":"https://lists.apache.org/thread.html/rdfa7b6253c4d6271e31566ecd5f30b7ce1b8fb2c89d52b8c4e0f4e30@%3Ccommits.tinkerpop.apache.org%3E"},{"type":"WEB","url":"https://security.netapp.com/advisory/ntap-20210706-0005"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T12:20:09.027755Z"}}