CVE-2025-27789

Babel has inefficient RegExp complexity in generated code with .replace when transpiling named capturing groups

Workarounds

If you are passing user-provided strings as the second argument of .replace on regular expressions that contain named capturing groups, validate the input and make sure it does not contain the substring $< if it's then not followed by > (possibly with other characters in between).

References

This vulnerability was reported and fixed in https://github.com/babel/babel/pull/17173.

When using Babel to compile regular expression named capturing groups, Babel will generate a polyfill for the .replace method that has quadratic complexity on some specific replacement pattern strings (i.e. the second argument passed to .replace).

Your generated code is vulnerable if all the following conditions are true:

• You use Babel to compile regular expression named capturing groups
• You use the .replace method on a regular expression that contains named capturing groups
• Your code uses untrusted strings as the second argument of .replace

If you are using @babel/preset-env with the targets option, the transform that injects the vulnerable code is automatically enabled if:

• you use duplicated named capturing groups, and target any browser older than Chrome/Edge 126, Opera 112, Firefox 129, Safari 17.4, or Node.js 23
• you use any named capturing groups, and target any browser older than Chrome 64, Opera 71, Edge 79, Firefox 78, Safari 11.1, or Node.js 10

You can verify what transforms @babel/preset-env is using by enabling the debug option.

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.

CVE-2025-27789 has a CVSS score of 6.2 (Medium). The vector is requires local access, 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 (7.26.10, 8.0.0-alpha.17); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

This problem has been fixed in @babel/helpers and @babel/runtime 7.26.10 and 8.0.0-alpha.17, please upgrade. It's likely that you do not directly depend on @babel/helpers, and instead you depend on @babel/core (which itself depends on @babel/helpers). Upgrading to @babel/core 7.26.10 is not required, but it guarantees that you are on a new enough @babel/helpers version.

Please note that just updating your Babel dependencies is not enough: you will also need to re-compile your code.

1. What is CVE-2025-27789? CVE-2025-27789 is a medium-severity inefficient regular expression (ReDoS) vulnerability in @babel/helpers (npm), affecting versions < 7.26.10. It is fixed in 7.26.10, 8.0.0-alpha.17. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. How severe is CVE-2025-27789? CVE-2025-27789 has a CVSS score of 6.2 (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 packages are affected by CVE-2025-27789?
   • @babel/helpers (npm) (versions < 7.26.10)
   • @babel/runtime (npm) (versions < 7.26.10)
   • @babel/runtime-corejs2 (npm) (versions < 7.26.10)
   • @babel/runtime-corejs3 (npm) (versions < 7.26.10)
4. Is there a fix for CVE-2025-27789? Yes. CVE-2025-27789 is fixed in 7.26.10, 8.0.0-alpha.17. Upgrade to this version or later.
5. Is CVE-2025-27789 exploitable, and should I be worried? Whether CVE-2025-27789 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-2025-27789 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-2025-27789?
   • Upgrade @babel/helpers to 7.26.10 or later
   • Upgrade @babel/runtime to 7.26.10 or later
   • Upgrade @babel/runtime-corejs2 to 7.26.10 or later
   • Upgrade @babel/runtime-corejs3 to 7.26.10 or later
   • Upgrade @babel/helpers to 8.0.0-alpha.17 or later
   • Upgrade @babel/runtime to 8.0.0-alpha.17 or later
   • Upgrade @babel/runtime-corejs2 to 8.0.0-alpha.17 or later
   • Upgrade @babel/runtime-corejs3 to 8.0.0-alpha.17 or later