CVE-2026-48125

A regular expression denial-of-service (ReDoS) vulnerability has been discovered in ua-parser-js when using the Client Hints API. By sending a crafted Sec-CH-UA-Model header to an application that calls UAParser(headers).withClientHints(), an attacker can cause the parser to spend excessive CPU time due to catastrophic backtracking in the device regex:

/ ([\w ]+) miui\/v?\d/i

Unlike when using the User-Agent value, which has a hard limit of UA_MAX_LENGTH = 500, when using Client Hints, values are copied without a length limit before being passed into regex parsing.

PoC

const { UAParser } = require('ua-parser-js');

const headers = {
  'sec-ch-ua-platform': '"Android"',
  'sec-ch-ua-mobile': '?1',
  'sec-ch-ua-model': '"' + 'A '.repeat(25000) + '"'
};

const t0 = process.hrtime.bigint();
UAParser(headers).withClientHints();
const ms = Number(process.hrtime.bigint() - t0) / 1e6;

if (ms > 100) {
  console.log('Potential ReDoS');
}

Affected Versions

ua-parser-js versions >=2.0.1, <=2.0.9 are affected. The withClientHints() API is not present in version 0.7.x or 1.x.

References

• Regular expression Denial of Service - ReDoS (OWASP)

Credits

Thanks to @sondt99, who first reported the issue.

This vulnerability allows an unauthenticated attacker to trigger a denial-of-service condition in any server-side application that uses UAParser(headers).withClientHints(). A single request with a ~32,000-character model value can consume over 400ms of CPU time, with parsing time growing polynomially with input length. The impact is availability only, there is no confidentiality or integrity impact.

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

CVE-2026-48125 has a CVSS score of 5.3 (Medium). 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 (2.0.10); upgrading removes the vulnerable code path.

Kodem intelligence

A patch has been released to fix the vulnerable regular expression and limit the Client Hints input. Users should update to version 2.0.10 or later.

1. What is CVE-2026-48125? CVE-2026-48125 is a medium-severity uncontrolled resource consumption vulnerability in ua-parser-js (npm), affecting versions >= 2.0.1, < 2.0.10. It is fixed in 2.0.10. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-48125? CVE-2026-48125 has a CVSS score of 5.3 (Medium). 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 ua-parser-js are affected by CVE-2026-48125? ua-parser-js (npm) versions >= 2.0.1, < 2.0.10 is affected.
4. Is there a fix for CVE-2026-48125? Yes. CVE-2026-48125 is fixed in 2.0.10. Upgrade to this version or later.
5. Is CVE-2026-48125 exploitable, and should I be worried? Whether CVE-2026-48125 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-2026-48125 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-2026-48125? Upgrade ua-parser-js to 2.0.10 or later.