CVE-2019-20920 is a high-severity (CVSS 8.1) Code Injection vulnerability in handlebars. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for handlebars — see the affected versions and patch details below.
Arbitrary Code Execution in Handlebars
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2019-20920.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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 |
Affected Products
handlebarshandlebarsjsResearch 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
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
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?
Find it across npm, including transitive dependencies.