CVE-2021-32640 is a medium-severity (CVSS 5.3) Uncontrolled Resource Consumption vulnerability in ws. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for ws — see the affected versions and patch details below.
ReDoS in Sec-Websocket-Protocol header
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
wsnpmDescription
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 [email protected] (https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff) and backported to [email protected] (https://github.com/websockets/ws/commit/78c676d2a1acefbc05292e9f7ea0a9457704bf1b) and [email protected] (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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | ws | ≥ 7.0.0&&< 7.4.6 | 7.4.6npm install ws@7.4.6 |
| 📦npm | ws | ≥ 6.0.0&&< 6.2.2 | 6.2.2npm install ws@6.2.2 |
| 📦npm | ws | ≥ 5.0.0&&< 5.2.3 | 5.2.3npm install ws@5.2.3 |
Affected Products
e-series performance analyzernetappwsws_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ws, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ws to 7.4.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32640 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
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.Source: Red Hat security advisory for CVE-2021-32640 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2021-32640 in your dependencies?
Find it across npm, including transitive dependencies.