MediumGHSA-6fc8-4gx4-v693CVE-2021-32640

ReDoS in Sec-Websocket-Protocol header

Published 28 May 2021 · Updated 8 Jul 2026

Affected packages

wsnpm

Affected: >=7.0.0 <7.4.6
Fixed in: 7.4.6

Update to the fixed version for your release line, for example:npm install ws@7.4.6

wsnpm

Affected: >=6.0.0 <6.2.2
Fixed in: 6.2.2

Update to the fixed version for your release line, for example:npm install ws@6.2.2

wsnpm

Affected: >=5.0.0 <5.2.3
Fixed in: 5.2.3

Update to the fixed version for your release line, for example:npm install ws@5.2.3

Details

Impact

A specially crafted value of the Sec-Websocket-Protocol header can be used to significantly slow down a ws server.

Proof of concept

for (const length of [1000, 2000, 4000, 8000, 16000, 32000]) {
  const value = 'b' + ' '.repeat(length) + 'x';
  const start = process.hrtime.bigint();

  value.trim().split(/ *, */);

  const end = process.hrtime.bigint();

  console.log('length = %d, time = %f ns', length, end - start);
}

Patches

The 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).

Workarounds

In 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` and/or the `maxHeaderSize` options.

Credits

The vulnerability was responsibly disclosed along with a fix in private by Robert McLaughlin from University of California, Santa Barbara.

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References

Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.