Summary
@isaacs/brace-expansion has Uncontrolled Resource Consumption
@isaacs/brace-expansion is vulnerable to a Denial of Service (DoS) issue caused by unbounded brace range expansion. When an attacker provides a pattern containing repeated numeric brace ranges, the library attempts to eagerly generate every possible combination synchronously. Because the expansion grows exponentially, even a small input can consume excessive CPU and memory and may crash the Node.js process.
Details
The vulnerability occurs because @isaacs/brace-expansion expands brace expressions without any upper bound or complexity limit. Expansion is performed eagerly and synchronously, meaning the full result set is generated before returning control to the caller.
For example, the following input:
{0..99}{0..99}{0..99}{0..99}{0..99}
produces:
100^5 = 10,000,000,000 combinations
This exponential growth can quickly overwhelm the event loop and heap memory, resulting in process termination.
Proof of Concept
The following script reliably triggers the issue.
Create poc.js:
const { expand } = require('@isaacs/brace-expansion');
const pattern = '{0..99}{0..99}{0..99}{0..99}{0..99}';
console.log('Starting expansion...');
expand(pattern);
Run it:
node poc.js
The process will freeze and typically crash with an error such as:
FATAL ERROR: JavaScript heap out of memory
Impact
This is a denial of service vulnerability. Any application or downstream dependency that uses @isaacs/brace-expansion on untrusted input may be vulnerable to a single-request crash.
An attacker does not require authentication and can use a very small payload to:
- Trigger exponential computation
- Exhaust memory and CPU resources
- Block the event loop
- Crash Node.js services relying on this library
A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-25547? CVE-2026-25547 is a high-severity inefficient regular expression (ReDoS) vulnerability in @isaacs/brace-expansion (npm), affecting versions <= 5.0.0. It is fixed in 5.0.1. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
- Which versions of @isaacs/brace-expansion are affected by CVE-2026-25547? @isaacs/brace-expansion (npm) versions <= 5.0.0 is affected.
- Is there a fix for CVE-2026-25547? Yes. CVE-2026-25547 is fixed in 5.0.1. Upgrade to this version or later.
- Is CVE-2026-25547 exploitable, and should I be worried? Whether CVE-2026-25547 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
- What actually determines whether CVE-2026-25547 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.
- How do I fix CVE-2026-25547? Upgrade
@isaacs/brace-expansionto 5.0.1 or later.