CVE-2025-27789 is a medium-severity (CVSS 6.2) CWE-1333 vulnerability in @babel/helpers. A fix is available for @babel/helpers — see the affected versions and patch details below.
Inefficient RexExp complexity in generated code with .replace when transpiling named capturing groups
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-27789.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-27789 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@babel/helpersnpm@babel/runtimenpm@babel/runtime-corejs2npmDescription
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
.replacemethod 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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @babel/helpers | all versions | 7.26.10npm install @babel/helpers@7.26.10 |
| 📦npm | @babel/runtime | all versions | 7.26.10npm install @babel/runtime@7.26.10 |
| 📦npm | @babel/runtime-corejs2 | all versions | 7.26.10npm install @babel/runtime-corejs2@7.26.10 |
| 📦npm | @babel/runtime-corejs3 | all versions | 7.26.10npm install @babel/runtime-corejs3@7.26.10 |
| 📦npm | @babel/helpers | ≥ 8.0.0-alpha.0&&< 8.0.0-alpha.17 | 8.0.0-alpha.17npm install @babel/helpers@8.0.0-alpha.17 |
| 📦npm | @babel/runtime | ≥ 8.0.0-alpha.0&&< 8.0.0-alpha.17 | 8.0.0-alpha.17npm install @babel/runtime@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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-27789 can be triaged on real exposure rather than presence alone.
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 Security finds CVE-2025-27789 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.