How severe is CVE-2021-23424?

CVE-2021-23424 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-23424?

CVE-2021-23424 affects the following packages: ansi-html (npm). Ecosystems affected: npm.

How do I fix CVE-2021-23424?

Update ansi-html to 0.0.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23424 is resolved across your whole dependency graph.

How do I detect CVE-2021-23424 in my npm dependencies?

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

How do I mitigate CVE-2021-23424 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-2021-23424 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-23424, including 3 in-the-wild exploitations 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-2021-23424?

CVE-2021-23424 has an EPSS (Exploit Prediction Scoring System) score of 2.0%, placing it in the 80th 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.

When was CVE-2021-23424 published, and has it been updated?

CVE-2021-23424 was published on September 2, 2021 and was last updated on November 8, 2023. 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-2021-23424 — ansi-html

HIGHFix: Tjatse/ansi-html@8142b25

CVE-2021-23424 is a high-severity (CVSS 7.5) vulnerability in ansi-html. 3 public exploit references exist, so weaponization risk is real. A fix is available for ansi-html — see the affected versions and patch details below.

Uncontrolled Resource Consumption in ansi-html

Published

Sep 2, 2021

Updated

Nov 8, 2023

Affected

1 pkg

Patched

1 / 1

Exploits

3 known

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

EPSS Exploitation Probability

via FIRST.org ↗

2.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs80th percentile — riskier than 80% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-23424 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 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.

522other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

ansi-htmlnpm

6.7Mdownloads / week

Description

This affects all versions of package ansi-html. If an attacker provides a malicious string, it will get stuck processing the input for an extremely long time.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`ansi-html`	all versions	0.0.8`npm install ansi-html@0.0.8`

Affected Products

1 product · 1 configurations

Application

ansi-htmlansi-html_project

< 0.0.8

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.

This affects all versions of package ansi-html. If an attacker provides …

snyk.ioNVDAug 2021

This affects all versions of package ansi-html. If an attacker provides …

snyk.ioNVDAug 2021

This affects all versions of package ansi-html. If an attacker provides …

github.comNVDAug 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ansi-html, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ansi-html to 0.0.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23424 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

This affects all versions of package ansi-html. If an attacker provides a malicious string, it will get stuck processing the input for an extremely long time.

O3 Security · Impact-Aware SCA

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CVE-2021-23424 — ansi-html

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-23424 in your dependencies?