No exploitation reportedFix available

CVE-2021-33587

Q: Is CVE-2021-33587 actively exploited?

Active exploitation of CVE-2021-33587 has not been confirmed. Its EPSS score was 2.0% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-33587?

CVE-2021-33587 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-05-28
Fixed in5.0.1

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

The css-what package 4.0.0 through 5.0.0 for Node.js does not ensure that attribute parsing has Linear Time Complexity relative to the size of the input.

Timeline

dates in UTC

2021-05-2820:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-33587?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-33587?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV · NVD

css-what

Branch	Affected	Fixed in	Source
5.0	≥ 4.0.0, < 5.0.1	5.0.1	OSV

Css-what project css-what

Branch	Affected	Fixed in	Source
4.0	= 4.0.0	no fix published	NVD
5.0	= 5.0.0	no fix published	NVD

Netapp e-series performance analyzer

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update css-what to 5.0.1

Advisories and patches

github.comPatch · Release Notes

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
FIRST EPSSEPSS score2.0 %2026-10-23
OSVaffected packages—

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-05-28
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-33587?

The css-what package 4.0.0 through 5.0.0 for Node.js does not ensure that attribute parsing has Linear Time Complexity relative to the size of the input.

Is CVE-2021-33587 actively exploited?

Active exploitation of CVE-2021-33587 has not been confirmed. Its EPSS score was 2.0% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-33587?

CVE-2021-33587 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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