CVE-2021-23470 is a critical-severity (CVSS 9.8) CWE-1321 vulnerability in putil-merge. 1 public exploit reference exists, so weaponization risk is real. A fix is available for putil-merge — see the affected versions and patch details below.
Prototype Pollution in putil-merge
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-23470 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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.
putil-mergenpmDescription
This affects the package putil-merge before 3.8.0. The merge() function does not check the values passed into the argument. An attacker can supply a malicious value by adjusting the value to include the constructor property. Note: This vulnerability derives from an incomplete fix in https://security.snyk.io/vuln/SNYK-JS-PUTILMERGE-1317077
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | putil-merge | all versions | 3.8.0npm install putil-merge@3.8.0 |
Affected Products
putil-mergeputil-merge_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for putil-merge, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update putil-merge to 3.8.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23470 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.
Frequently Asked Questions
Is CVE-2021-23470 in your dependencies?
Find it across npm, including transitive dependencies.