CVE-2021-3749: axios ReDoS
CVE-2021-3749 (axios ReDoS) is a regular expression denial of service (redos) vulnerability in axios (npm). As of 2026-06-18 it carries a 7.9% probability of exploitation in the next 30 days (EPSS). It is fixed in 0.21.2 — if you depend on an earlier version, upgrade.
| Severity | Medium |
|---|---|
| CVSS vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| EPSS (exploit probability, 30d) | 7.9% · 94th percentile |
| Vulnerability type | Regular Expression Denial of Service (ReDoS) |
| Affected package | axios (npm) |
| Fixed in | 0.21.2 |
What is CVE-2021-3749?
axios before 0.21.2 is vulnerable to inefficient regular-expression complexity when trimming header values, so an attacker-controlled response can hang the event loop and cause a denial of service.
Is CVE-2021-3749 exploitable?
CVE-2021-3749 has an EPSS score of 7.9% (94th percentile), meaning a 7.9% probability of exploitation in the next 30 days. Its CVSS vector is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, which scores as Medium severity. It is a regular expression denial of service (redos) issue.
What is the EPSS score for CVE-2021-3749?
As of 2026-06-18, the EPSS exploit-prediction score for CVE-2021-3749 is 7.9% (94th percentile). EPSS estimates the probability that a vulnerability will be exploited in the wild within the next 30 days and is recomputed daily by FIRST.org.
How do I fix CVE-2021-3749?
Upgrade axios to 0.21.2 or later. axios before 0.21.2 is vulnerable to inefficient regular-expression complexity when trimming header values, so an attacker-controlled response can hang the event loop and cause a denial of service.
Am I affected by CVE-2021-3749?
You are affected if your project (directly or transitively) depends on a vulnerable version of axios in the npm ecosystem. Check your lockfile for the resolved version, or scan automatically with VulnFeed.
Check your own project automatically
Don't eyeball every dependency by hand. VulnFeed reads your lockfile, checks it against the same advisory data, and ranks findings by EPSS — free, no signup (10 scans/day):
curl -s https://vulnfeed-api.novadyne.ai/vulnscan/query \
-H 'content-type: application/json' \
-d '{"ecosystem":"npm","package":"PKG","version":"VERSION"}'
Or run it inside Claude Code with no API key — uvx vulnfeed-mcp — and just ask "scan this project for vulnerabilities."
Data sources: vulnerability metadata from OSV.dev and the National Vulnerability Database; exploit-probability (EPSS) from FIRST.org (recomputed daily; EPSS data shown here as of 2026-06-18). Page generated 2026-06-18.