---
id: "CVE-2026-109924"
kind: "vulnerability"
aliases: ["CVE-2026-109924", "GHSA-4qv8-2p9j-2685"]
title: "undici vulnerable to Denial of Service via unbounded memory in the EventSource parser"
severity: "high"
cvss: 7.5
epss: 0.00321
exploited: false
status: "open"
category: "package"
products: [{"name": "undici", "fixed": ["6.29.1"], "affected": ">= 6.5.0, < 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": ">= 6.5.0, < 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: ["backend", "cwe-770", "node.js", "npm", "package", "undici"]
not_affected_if: ["no-eventsource-usage", "trusted-peers-only"]
published_at: "2026-10-15T19:17:22+00:00"
first_seen_at: "2026-10-23T22:15:56+00:00"
updated_at: "2026-10-25T03:25:23+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-4qv8-2p9j-2685", "first_seen_at": "2026-10-23T22:15:56+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-109924", "first_seen_at": "2026-10-23T23:44:52+00:00"}]
---

# undici vulnerable to Denial of Service via unbounded memory in the EventSource parser

The undici HTTP client for Node.js keeps growing parser state while reading Server-Sent Events, so a malicious or compromised SSE server can drive memory use up. A small compressed response can expand into enough retained memory to crash the process, which is a denial of service with no code execution.

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

## Affected

- npm:undici affected >= 6.5.0, < 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 >= 6.5.0, < 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 each project that depends on undici, and check whether the output falls in an affected range (6.5.0 to 6.29.0, 7.0.0 to 7.30.0, or 8.0.0 to 8.12.1).
- Search code for `EventSource` from undici to see whether the application keeps SSE connections open to peers it does not control.

## Fix

- Upgrade undici to `6.29.1`, `7.30.1`, or `8.12.2` (or later in the same major line).
- No workaround is documented by the sources; upgrading is the fix.

## Timeline

- 2026-10-23T22:15:56+00:00 ghsa https://github.com/advisories/GHSA-4qv8-2p9j-2685
- 2026-10-23T23:44:52+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-109924

## From the sources

undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its EventSource client can be driven to exhaust process memory by a malicious or compromised Server-Sent Events peer. By sending millions of tiny completed data fields with no blank event separator, or a single unfinished line split across many chunks, the parser retains a growing amount of per-field and per-chunk state that the byte-based maxEventSize and maxResponseSize limits do not bound, and because maxResponseSize is enforced on the compressed body before decompression, a small compressed response can expand into enough retained memory to terminate the process. An application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response, and availability is the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which bound the retained parser state independently of the byte limits, and users should upgrade to one of those versions or later. There is no workaround.

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