---
id: "CVE-2026-109932"
kind: "vulnerability"
aliases: ["CVE-2026-109932", "GHSA-9fm3-97px-rjf6"]
title: "undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering"
severity: "high"
cvss: 7.5
epss: 0.00321
exploited: false
status: "open"
category: "package"
products: [{"name": "undici", "fixed": ["6.29.1"], "affected": ">= 5.15.0, < 6.29.1", "ecosystem": "npm"}, {"name": "undici", "fixed": ["7.30.1"], "affected": ">= 7.0.0, < 7.30.1", "ecosystem": "npm"}, {"name": "undici", "fixed": ["8.12.2"], "affected": ">= 8.0.0, < 8.12.2", "ecosystem": "npm"}, {"name": "nodejs undici", "fixed": ["6.29.1"], "affected": ">= 5.15.0, < 6.29.1", "ecosystem": "vendor"}, {"name": "nodejs undici", "fixed": ["7.30.1"], "affected": ">= 7.0.0, < 7.30.1", "ecosystem": "vendor"}, {"name": "nodejs undici", "fixed": ["8.12.2"], "affected": ">= 8.0.0, < 8.12.2", "ecosystem": "vendor"}]
ecosystems: ["npm", "vendor"]
tags: ["cwe-400", "cwe-405", "cwe-770", "node.js", "npm", "package", "undici", "websocket-clients"]
not_affected_if: ["no-websocket-client", "trusted-servers-only"]
published_at: "2026-10-15T19:17:22+00:00"
first_seen_at: "2026-10-27T19:04:56+00:00"
updated_at: "2026-10-27T19:33:18+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-9fm3-97px-rjf6", "first_seen_at": "2026-10-27T19:04:56+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-109932", "first_seen_at": "2026-10-27T19:33:18+00:00"}]
---

# undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering

The undici WebSocket client, including Node.js's built-in globalThis.WebSocket, automatically answers every PING frame without respecting write backpressure. A malicious or compromised WebSocket server that sends small PINGs and never reads the PONGs makes the outbound queue grow until the process runs out of memory and crashes.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- npm:undici affected >= 5.15.0, < 6.29.1 fixed 6.29.1
- npm:undici affected >= 7.0.0, < 7.30.1 fixed 7.30.1
- npm:undici affected >= 8.0.0, < 8.12.2 fixed 8.12.2
- vendor:nodejs undici affected >= 5.15.0, < 6.29.1 fixed 6.29.1
- vendor:nodejs undici affected >= 7.0.0, < 7.30.1 fixed 7.30.1
- vendor:nodejs undici affected >= 8.0.0, < 8.12.2 fixed 8.12.2

## How to check

- Run `node -p "require('undici/package.json').version"` in the project to see the installed undici version
- Run `npm ls undici` to find every copy, including ones pulled in transitively
- Check whether the app opens WebSocket connections to servers it does not fully control, via `globalThis.WebSocket` or `new WebSocket(` in the code

## Fix

- Upgrade undici to `6.29.1` on the 6.x line, `7.30.1` on the 7.x line, or `8.12.2` on the 8.x line
- Upgrade Node.js to a release that bundles a fixed undici, if the app relies on the built-in `globalThis.WebSocket`
- No workaround is documented by the sources

## Timeline

- 2026-10-27T19:04:56+00:00 ghsa https://github.com/advisories/GHSA-9fm3-97px-rjf6
- 2026-10-27T19:33:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-109932

## From the sources

undici is an HTTP client library for Node.js. In versions 5.15.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its WebSocket client, including the bundled WebSocket exposed by Node.js, can be driven to exhaust process memory by a malicious or compromised WebSocket server. For every PING frame received, the client automatically writes a PONG response and ignores the backpressure signal from the socket write, so a server that streams small PING frames while never reading the client's PONGs makes the outbound write queue and heap grow without bound until the Node.js process runs out of memory and terminates. The attack is remote and unauthenticated, needs only a normal WebSocket connection, and is asymmetric, since small inbound PINGs produce a much larger retained outbound queue, with availability the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which pause WebSocket frame parsing when the automatic PONG response hits socket backpressure and resume on drain, bounding the outbound queue, and users should upgrade to one of those versions or later. There is no workaround.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_