CVE-2025-27789 is a medium-severity (CVSS 6.2) CWE-1333 vulnerability in @babel/helpers. O3 Security confirms whether CVE-2025-27789 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Inefficient RexExp complexity in generated code with .replace when transpiling named capturing groups
Real-World Exposure
@babel/helpers📦@babel/runtime📦@babel/runtime-corejs2📦@babel/runtime-corejs3📦@babel/helpers📦@babel/runtime📦@babel/runtime-corejs2📦@babel/runtime-corejs3Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @babel/helpers | all versions | 7.26.10 |
| 📦npm | @babel/runtime | all versions | 7.26.10 |
| 📦npm | @babel/runtime-corejs2 | all versions | 7.26.10 |
| 📦npm | @babel/runtime-corejs3 | all versions | 7.26.10 |
| 📦npm | @babel/helpers | ≥ 8.0.0-alpha.0&&< 8.0.0-alpha.17 | 8.0.0-alpha.17 |
| 📦npm | @babel/runtime | ≥ 8.0.0-alpha.0&&< 8.0.0-alpha.17 | 8.0.0-alpha.17 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @babel/helpers. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @babel/helpers to 7.26.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-27789 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2025-27789 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2025-27789. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-27789 in your dependencies?
O3 detects CVE-2025-27789 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.