CVE-2021-23358 is a high-severity (CVSS 7.2) Code Injection vulnerability in underscore. 4 public exploit references exist, so weaponization risk is real. A fix is available for underscore — see the affected versions and patch details below.
Arbitrary Code Execution in underscore
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.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-23358.
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-2021-23358 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.
underscorenpmDescription
The package underscore from 1.13.0-0 and before 1.13.0-2, from 1.3.2 and before 1.12.1 are vulnerable to Arbitrary Code Injection via the template function, particularly when a variable property is passed as an argument as it is not sanitized.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | underscore | ≥ 1.3.2&&< 1.12.1 | 1.12.1npm install underscore@1.12.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
The package underscore from 1.13.0-0 and before 1.13.0-2, from 1.3.2 and…
The package underscore from 1.13.0-0 and before 1.13.0-2, from 1.3.2 and…
The package underscore from 1.13.0-0 and before 1.13.0-2, from 1.3.2 and…
The package underscore from 1.13.0-0 and before 1.13.0-2, from 1.3.2 and…
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for underscore, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update underscore to 1.12.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23358 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-2021-23358 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-23358. 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.
Whilst the OpenShift Container Platform (OCP) openshift4/ose-grafana and openshift3/grafana as well as console, grc-ui and search-ui containers for Red Hat Advanced Management for Kubernetes (RHACM) include the vulnerable underscore library, the access to it is protected by OpenShift OAuth. Additionally this library…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Advanced Cluster Management for Kubernetes 2.0 for RHEL 8 | rhacm2/acm-operator-bundle:v2.0.10-8 | RHSA-2021:1448 |
| Red Hat Ceph Storage 7.1 | ceph-2:18.2.1-381.el8cp | RHSA-2026:2769 |
| Red Hat Virtualization Engine 4.4 | ovirt-engine-ui-extensions-0:1.2.7-1.el8ev | RHSA-2021:2865 |
| Red Hat Virtualization Engine 4.4 | ovirt-web-ui-0:1.9.1-1.el8ev | RHSA-2022:6393 |
| Red Hat Ceph Storage 8 | rhceph/grafana-rhel9:1770630607 | RHSA-2026:2737 |
| Red Hat Ceph Storage 9 | rhceph/grafana-rhel10:1771399331 | RHSA-2026:3406 |
Frequently Asked Questions
Is CVE-2021-23358 in your dependencies?
O3 Security finds CVE-2021-23358 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.