Regular Expression Denial of Service

Overview

In ws before versions 5.2.3, 6.2.2 and 7.4.6 there is a ReDOS vulnerability.

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).

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.

Recommendation

Upgrade to version 5.2.3 or 6.2.2 or 7.4.6 or later

References

• CVE
• GitHub Advisory