CVE-2019-20920 is a high-severity (CVSS 8.1) Code Injection vulnerability in handlebars. 1 public exploit reference exists, so weaponization risk is real. A fix is available for handlebars — see the affected versions and patch details below.
Arbitrary Code Execution in Handlebars
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-2019-20920 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.
handlebarsnpmDescription
Handlebars before 3.0.8 and 4.x before 4.5.3 is vulnerable to Arbitrary Code Execution. The lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript. This can be used to run arbitrary code on a server processing Handlebars templates or in a victim's browser (effectively serving as XSS).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | handlebars | all versions | 3.0.8npm install handlebars@3.0.8 |
| 📦npm | handlebars | ≥ 4.0.0&&< 4.5.3 | 4.5.3npm install handlebars@4.5.3 |
Research 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 handlebars, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update handlebars to 3.0.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-20920 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-2019-20920 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2019-20920. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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 Quay includes Handlebars.js as a development dependency. It does not use Handlebars.js at runtime to process templates, so it has been given a low impact rating. Red Hat Virtualization includes Handlebars.js in two components. In ovirt-engine-ui-extentions, the version used is newer and is not affected by this…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift Container Platform 4.6 | openshift4/ose-logging-kibana6:v4.6.0-202106181629.p0.git.40f3e72 | RHSA-2021:2500 |
| Red Hat Quay 3 | quay/quay-rhel8:v3.6.0-62 | RHSA-2021:3917 |
| Red Hat Virtualization Engine 4.4 | ovirt-web-ui-0:1.6.5-1.el8ev | RHSA-2020:5179 |
| RHPAM 7.13.1 async | handlebars | RHSA-2023:1334 |
Frequently Asked Questions
Is CVE-2019-20920 in your dependencies?
O3 Security finds CVE-2019-20920 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.