CVE-2021-33502: 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 (regula

Q: How do I fix CVE-2021-33502?

normalize-url: upgrade to 4.5.1, 5.3.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-33502 being exploited?

CVE-2021-33502 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-33502 affect?

CVE-2021-33502 affects normalize-url. Severity is high (CVSS 7.5). 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.

Q: How urgent is CVE-2021-33502?

Priority 51/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2021-33502 is a high-severity flaw (CVSS 7.5) affecting normalize-url. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Weakness	CWE-1333
Published	2021-05-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: normalize-url project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-05-24 16:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

normalize-url project normalize-url UPGRADE

Affected: >= 4.3.0 and < 4.5.1 · >= 5.0.0 and < 5.3.1 · 6.0.0

Fixed in: 4.5.1, 5.3.1

Safe to downgrade to: a release before 4.3.0

1. Check installed version

npm ls normalize-url

2. UPGRADE to 4.5.1

npm install normalize-url@">=4.5.1"

3. If no update is available yet, DOWNGRADE to a release before 4.3.0

npm view normalize-url versions npm install normalize-url@"<4.3.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-33502?

normalize-url: upgrade to 4.5.1, 5.3.1. Exact commands for each OS are on this page.

Is CVE-2021-33502 being exploited?

CVE-2021-33502 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-33502 affect?

CVE-2021-33502 affects normalize-url. Severity is high (CVSS 7.5). 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.

How urgent is CVE-2021-33502?

Priority 51/100. High severity; Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities

References

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