CVE-2021-23383 is a critical-severity (CVSS 9.8) CWE-1321 vulnerability in handlebars. 4 public exploit references exist, so weaponization risk is real. A fix is available for handlebars — see the affected versions and patch details below.
Prototype Pollution in handlebars
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-23383 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.
handlebarsnpmDescription
The package handlebars before 4.7.7 are vulnerable to Prototype Pollution when selecting certain compiling options to compile templates coming from an untrusted source.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | handlebars | all versions | 4.7.7npm install handlebars@4.7.7 |
Affected Products
handlebarshandlebarsjse-series performance analyzernetappResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
The package handlebars before 4.7.7 are vulnerable to Prototype Pollutio…
The package handlebars before 4.7.7 are vulnerable to Prototype Pollutio…
The package handlebars before 4.7.7 are vulnerable to Prototype Pollutio…
The package handlebars before 4.7.7 are vulnerable to Prototype Pollutio…
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for handlebars, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update handlebars to 4.7.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23383 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat OpenShift Container Platform (OCP) 4 delivers the kibana component which includes Handlebars.js. Starting in 4.6, kibana is shipping as "container first" content. As such, the fix for OCP will be seen in the affected products table under openshift4/ose-logging-kibana6. The separate package "kibana" listed…
| Product | Fixed in | Advisory |
|---|---|---|
| OpenShift Logging 5.1 | openshift-logging/kibana6-rhel8:v6.8.1-48 | RHSA-2021:4628 |
| OpenShift Logging 5.2 | openshift-logging/kibana6-rhel8:v6.8.1-47 | RHSA-2021:4032 |
| Red Hat OpenShift Container Platform 4.6 | openshift4/ose-logging-kibana6:v4.6.0-202106181629.p0.git.40f3e72 | RHSA-2021:2500 |
| RHPAM 7.13.1 async | handlebars | RHSA-2023:1334 |
Frequently Asked Questions
Is CVE-2021-23383 in your dependencies?
Find it across npm, including transitive dependencies.