CVE-2025-27789: Inefficient RexExp complexity in generated code with .replace when transpiling named capturing groups
Impact
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.
Patches
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.
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.
Other sources
Babel is a compiler for writing next generation JavaScript. When using versions of Babel prior to 7.26.10 and 8.0.0-alpha.17 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). Generated code is vulnerable if all the following conditions are true: Using Babel to compile regular expression named capturing groups, using the .replace method on a regular expression that contains named capturing groups, and the code using untrusted strings as the second argument of .replace. This problem has been fixed in @babel/helpers and @babel/runtime 7.26.10 and 8.0.0-alpha.17. It's likely that individual users do not directly depend on @babel/helpers, and instead depend on @babel/core (which itself depends on @babel/helpers). Upgrading to @babel/core 7.26.10 is not required, but it guarantees use of a new enough @babel/helpers version. Note that just updating Babel dependencies is not enough; one will also need to re-compile the code. No known workarounds are available.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2025-27789?
CVE-2025-27789 has a high severity due to potential performance issues caused by quadratic complexity in the polyfill.
How do I fix CVE-2025-27789?
To fix CVE-2025-27789, you should upgrade Babel to version 7.26.10 or later, or to 8.0.0-alpha.17 or later.
What products are affected by CVE-2025-27789?
CVE-2025-27789 affects Babel versions prior to 7.26.10 and 8.0.0-alpha.17, including @babel/core.
What is the impact of CVE-2025-27789?
The impact of CVE-2025-27789 includes significant performance degradation when using named capturing groups in regular expressions.
When was CVE-2025-27789 published?
CVE-2025-27789 was published as part of ongoing security advisories for Babel, highlighting issues discovered in previous versions.