CVE-2021-3801 is a medium-severity (CVSS 6.5) CWE-1333 vulnerability in prismjs. 1 public exploit reference exists, so weaponization risk is real. A fix is available for prismjs — see the affected versions and patch details below.
prismjs Regular Expression Denial of Service vulnerability
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-3801 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
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.
prismjsnpmDescription
Prism is a syntax highlighting library. The prismjs package is vulnerable to ReDoS (regular expression denial of service). An attacker that is able to provide a crafted HTML comment as input may cause an application to consume an excessive amount of CPU.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | prismjs | all versions | 1.25.0npm install prismjs@1.25.0 |
Affected Products
prismprismjsResearch 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 prismjs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update prismjs to 1.25.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3801 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
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.
OpenShift Container Platform (OCP) grafana-container does package a vulnerable verison of prismjs. However due to the instance being read only and behind OpenShift OAuth, it has been given a Low impact. Additionally it has been marked as wont-fix at this time and may be fixed in a future release. Just as OCP,…
| Product | Fixed in | Advisory |
|---|---|---|
| RHACS-3.67-RHEL-8 | advanced-cluster-security/rhacs-rhel8-operator:3.67.0-3 | RHSA-2021:4902 |
Frequently Asked Questions
Is CVE-2021-3801 in your dependencies?
Find it across npm, including transitive dependencies.