CVE-2021-33502 is a high-severity (CVSS 7.5) CWE-1333 vulnerability in normalize-url. A fix is available for normalize-url — see the affected versions and patch details below.
ReDoS in normalize-url
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-33502 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
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.
normalize-urlnpmDescription
The normalize-url package before 4.5.1, 5.x before 5.3.1, and 6.x before 6.0.1 for Node.js has a ReDoS (regular expression denial of service) issue because it has exponential performance for data: URLs.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | normalize-url | ≥ 4.3.0&&< 4.5.1 | 4.5.1npm install normalize-url@4.5.1 |
| 📦npm | normalize-url | ≥ 5.0.0&&< 5.3.1 | 5.3.1npm install normalize-url@5.3.1 |
| 📦npm | normalize-url | ≥ 6.0.0&&< 6.0.1 | 6.0.1npm install normalize-url@6.0.1 |
Affected Products
normalize-urlnormalize-url_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for normalize-url, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update normalize-url to 4.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33502 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.
| 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 8.4 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 Software Collections for Red Hat Enterprise Linux 7 | rh-nodejs12-nodejs-0:12.22.2-1.el7 | RHSA-2021:2931 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7 | rh-nodejs14-nodejs-0:14.17.2-1.el7 | RHSA-2021:2932 |
| Red Hat Virtualization Engine 4.4 | ovirt-engine-ui-extensions-0:1.3.3-1.el8ev | RHSA-2022:4711 |
Frequently Asked Questions
Is CVE-2021-33502 in your dependencies?
Find it across npm, including transitive dependencies.