Is CVE-2021-33391 in the CISA KEV catalog?

No. CVE-2021-33391 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-33391?

CVE-2021-33391 has a CVSS v3 base score of 9.8 (CRITICAL).

What is the EPSS score for CVE-2021-33391?

CVE-2021-33391 has an EPSS score of 1.13% (62th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-33391?

Upgrade tidy-html5 on debian 13 to 2:5.8.0-2 or later. Fixes are available for 4 affected products.

CVE & CISA-KEV Catalog

CVE-2021-33391

CRITICAL

9.8

CVSS v3

NVD

Description

An issue in HTACG HTML Tidy v5.7.28 allows attacker to execute arbitrary code via the -g option of the CleanNode() function in gdoc.c.

CWE-416Use After Free

How to fix

Remediation Available

tidy-html5Debian

Fixed in:2:5.8.0-2CVE-2021-33391

libtidy5deb1Ubuntu

Fixed in:2:5.6.0-11ubuntu0.20.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.22.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.10.1USN-6483-1

tidyUbuntu

Fixed in:2:5.6.0-11ubuntu0.20.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.22.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.10.1USN-6483-1

tidy-html5Ubuntu

Fixed in:2:5.6.0-11ubuntu0.20.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.22.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.04.1USN-6483-1

Fixed in:2:5.6.0-11ubuntu0.23.10.1USN-6483-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

1.13%probability of exploitation in 30 days

62ndpercentile

Moderate risk: more likely to be exploited than 62% of all known CVEs.

References

Patch1

github.com

Related Vulnerabilities

Other CWE-416 (Use After Free) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2019-0708	Critical	9.8	100%	KEV + Ransom	-
CVE-2021-31166	Critical	9.8	100%	KEV	Fix
CVE-2015-5119	Critical	9.8	99%	KEV	-
CVE-2010-3962	High	8.1	97%	KEV	-
CVE-2015-0313	Critical	9.8	96%	KEV	Fix
CVE-2017-9798	High	7.5	95%	-	Fix

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Markdown

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HTML

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-03-18.