Medium

ReDoS in Sec-Websocket-Protocol header

Disclosed: 28.05.2021
Updated: 11.10.2026 10:22

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.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	ws	>= 7.0.0, < 7.4.6, >= 6.0.0, < 6.2.2, >= 5.0.0, < 5.2.3	7.4.6, 6.2.2, 5.2.3

References

CVSS score 5.3/10

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE): CWE-345, CWE-400
Platform: npm
Package: ws
Disclosed: 28.05.2021
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-6fc8-4gx4-v693 - CC BY 4.0

Vulnerability history: ws

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries: 7
First → latest: 02.2019 06.2026
Without a fix: 0
Exploited in attacks: 0

Severity breakdown

High 4
Medium 2
Low 1

Disclosures per year

2019: 3
2020: 0
2021: 1
2022: 0
2023: 0
2024: 1
2025: 0
2026: 2

15.06.2026

ws: Memory exhaustion DoS from tiny fragments and data chunks

High · 7.5 CVE-2026-48779 >= 1.1.0, < 5.2.5, >= 6.0.0, < 6.2.4, >= 7.0.0, < 7.5.11, >= 8.0.0, < 8.21.0 5.2.5, 6.2.4, 7.5.11, 8.21.0
18.05.2026

ws: Uninitialized memory disclosure

Medium · 4.4 CVE-2026-45736 >= 8.0.0, < 8.20.1 8.20.1
17.06.2024

ws affected by a DoS when handling a request with many HTTP headers

High · 7.5 CVE-2024-37890 >= 2.1.0, < 5.2.4, >= 6.0.0, < 6.2.3, >= 7.0.0, < 7.5.10, >= 8.0.0, < 8.17.1 5.2.4, 6.2.3, 7.5.10, 8.17.1
28.05.2021

ReDoS in Sec-Websocket-Protocol header this entry

Medium · 5.3 CVE-2021-32640 >= 7.0.0, < 7.4.6, >= 6.0.0, < 6.2.2, >= 5.0.0, < 5.2.3 7.4.6, 6.2.2, 5.2.3
04.06.2019

Denial of Service in ws

High · 7.5 ghsa-5v72-xg48-5rpm >= 0.6.0, < 1.1.5, >= 2.0.0, < 3.3.1 1.1.5, 3.3.1
18.02.2019

DoS due to excessively large websocket message in ws

High CVE-2016-10542 < 1.1.1 1.1.1
18.02.2019

Remote Memory Disclosure in ws

Low CVE-2016-10518 < 1.0.1 1.0.1

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