CVE-2021-3807 is a high-severity (CVSS 7.5) CWE-1333 vulnerability in ansi-regex. 1 public exploit reference exists, so weaponization risk is real. A fix is available for ansi-regex — see the affected versions and patch details below.
Inefficient Regular Expression Complexity in chalk/ansi-regex
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-2021-3807.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-3807 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 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.
ansi-regexnpmDescription
ansi-regex is vulnerable to Inefficient Regular Expression Complexity which could lead to a denial of service when parsing invalid ANSI escape codes.
Proof of Concept
import ansiRegex from 'ansi-regex';
for(var i = 1; i <= 50000; i++) {
var time = Date.now();
var attack_str = "\u001B["+";".repeat(i*10000);
ansiRegex().test(attack_str)
var time_cost = Date.now() - time;
console.log("attack_str.length: " + attack_str.length + ": " + time_cost+" ms")
}
The ReDOS is mainly due to the sub-patterns [[\\]()#;?]* and (?:;[-a-zA-Z\\d\\/#&.:=?%@~_]*)*
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | ansi-regex | ≥ 6.0.0&&< 6.0.1 | 6.0.1npm install ansi-regex@6.0.1 |
| 📦npm | ansi-regex | ≥ 5.0.0&&< 5.0.1 | 5.0.1npm install ansi-regex@5.0.1 |
| 📦npm | ansi-regex | ≥ 4.0.0&&< 4.1.1 | 4.1.1npm install ansi-regex@4.1.1 |
| 📦npm | ansi-regex | ≥ 3.0.0&&< 3.0.1 | 3.0.1npm install ansi-regex@3.0.1 |
Affected Products
ansi-regexansi-regex_projectcommunications cloud native core policyoracleResearch 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 ansi-regex, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ansi-regex to 6.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3807 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.
This flaw requires crafted invalid ANSI escape codes in order to be exploited and only allows for denial of service of applications on the client side, hence the impact has been rated as Moderate. In Red Hat Virtualization and Red Hat Quay some components use a vulnerable version of ansi-regex. However, all frontend…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 8 | nodejs:16-8050020211206113934.c5368500 | RHSA-2021:5171 |
| Red Hat Enterprise Linux 8 | nodejs:14-8050020211213115342.c5368500 | RHSA-2022:0350 |
| Red Hat Enterprise Linux 8 | nodejs:16-8060020220805104227.ad008a3a | RHSA-2022:6449 |
| Red Hat Enterprise Linux 8.4 Extended Update Support | nodejs:14-8040020211213111158.522a0ee4 | RHSA-2022:0246 |
| Red Hat Enterprise Linux 9 | nodejs-nodemon-0:2.0.19-1.el9_0 | RHSA-2022:6595 |
| Red Hat Fuse 7.11 | io.hawt-hawtio-online | RHSA-2022:5532 |
| Red Hat Migration Toolkit for Containers 1.6 | rhmtc/openshift-migration-ui-rhel8:v1.6.5-8 | RHSA-2022:4814 |
| Red Hat Migration Toolkit for Containers 1.7 | rhmtc/openshift-migration-ui-rhel8:v1.7.2-9 | RHSA-2022:5483 |
Frequently Asked Questions
Is CVE-2021-3807 in your dependencies?
Find it across npm, including transitive dependencies.