How severe is CVE-2021-21384?

CVE-2021-21384 has a CVSS score of 7.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-21384?

CVE-2021-21384 affects the following packages: shescape (npm). Ecosystems affected: npm.

How do I fix CVE-2021-21384?

Update shescape to 1.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21384 is resolved across your whole dependency graph.

How do I detect CVE-2021-21384 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for shescape, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-21384 if there is no patch (or I can't update yet)?

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.

Is CVE-2021-21384 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-21384, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-21384?

CVE-2021-21384 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 46th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-21384?

CVE-2021-21384 is classified as CWE-88 (CWE-88). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-21384 published, and has it been updated?

CVE-2021-21384 was published on March 19, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

CVE-2021-21384 — shescape

HIGHFix: ericcornelissen/shescape@07a069a

CVE-2021-21384 is a high-severity (CVSS 7.8) CWE-88 vulnerability in shescape. 1 public exploit reference exists, so weaponization risk is real. A fix is available for shescape — see the affected versions and patch details below.

Null characters not escaped

Also known asGHSA-f2rp-38vg-j3gh

Published

Mar 19, 2021

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs46th percentile — riskier than 46% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-21384 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

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.

23other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

shescapenpm

22Kdownloads / week

Description

Impact

Anyone using Shescape to defend against shell injection may still be vulnerable against shell injection if the attacker manages to insert a null character into the payload. For example (on Windows):

const cp = require("child_process");
const shescape = require("shescape");

const nullChar = String.fromCharCode(0);
const payload = "foo\" && ls -al ${nullChar} && echo \"bar";
console.log(cp.execSync(`echo ${shescape.quote(payload)}`));
// foototal 3
// drwxr-xr-x 1 owner XXXXXX      0 Mar 13 18:44 .
// drwxr-xr-x 1 owner XXXXXX      0 Mar 13 00:09 ..
// drwxr-xr-x 1 owner XXXXXX      0 Mar 13 18:42 folder                                                                 
// -rw-r--r-- 1 owner XXXXXX      0 Mar 13 18:42 file

Patches

The problem has been patched in v1.1.3 which you can upgrade to now. No further changes are required.

Workarounds

Alternatively, null characters can be stripped out manually using e.g. arg.replace(/\u{0}/gu, "")

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`shescape`	all versions	1.1.3`npm install shescape@1.1.3`

Affected Products

1 product · 1 configurations

Application

shescapeshescape_project

< 1.1.3

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

shescape is a simple shell escape package for JavaScript. In shescape be…

github.comNVDApr 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for shescape, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update shescape to 1.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21384 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

### Impact Anyone using _Shescape_ to defend against shell injection may still be vulnerable against shell injection if the attacker manages to insert a [null character](https://en.wikipedia.org/wiki/Null_character) into the payload. For example (on Windows): ```javascript const cp = require("child_process"); const shescape = require("shescape"); const nullChar = String.fromCharCode(0); const payload = "foo\" && ls -al ${nullChar} && echo \"bar"; console.log(cp.execSync(`echo ${shescape.quote(payload)}`)); // foototal 3 // drwxr-xr-x 1 owner XXXXXX 0 Mar 13 18:44 . // drwxr-xr-x 1 owne