Is CVE-2021-3517 in the CISA KEV catalog?

No. CVE-2021-3517 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-3517?

CVE-2021-3517 has a CVSS v3 base score of 8.6 (HIGH).

What is the EPSS score for CVE-2021-3517?

CVE-2021-3517 has an EPSS score of 8.28% (94th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-3517?

Upgrade libxml2 on debian 11 to 2.9.10+dfsg-6.6 or later. Fixes are available for 3 affected products.

CVE & CISA-KEV Catalog

CVE-2021-3517

HIGHEPSS 94th pctl

8.6

CVSS v3

NVD

Description

There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11. An attacker who is able to supply a crafted file to be processed by an application linked with the affected functionality of libxml2 could trigger an out-of-bounds read. The most likely impact of this flaw is to application availability, with some potential impact to confidentiality and integrity if an attacker is able to use memory information to further exploit the application.

CWE-787Out-of-bounds Write CWE-125Out-of-bounds Read

How to fix

Remediation Available

libxml2Debian

Fixed in:2.9.10+dfsg-6.6CVE-2021-3517

libxml2Ubuntu

Fixed in:2.9.1+dfsg1-3ubuntu4.13+esm2USN-4991-1

Fixed in:2.9.3+dfsg1-1ubuntu0.7+esm1USN-4991-1

Fixed in:2.9.4+dfsg1-6.1ubuntu1.4USN-4991-1

Fixed in:2.9.10+dfsg-5ubuntu0.20.04.1USN-4991-1

libxml2-utilsUbuntu

Fixed in:2.9.1+dfsg1-3ubuntu4.13+esm2USN-4991-1

Fixed in:2.9.3+dfsg1-1ubuntu0.7+esm1USN-4991-1

Fixed in:2.9.4+dfsg1-6.1ubuntu1.4USN-4991-1

Fixed in:2.9.10+dfsg-5ubuntu0.20.04.1USN-4991-1

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

ConfidentialityLow

IntegrityLow

AvailabilityHigh

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

Exploit Intelligence

8.28%probability of exploitation in 30 days

94thpercentile

High risk: more likely to be exploited than 94% of all known CVEs.

References

Patch4

Third-Party Advisory4

Other references5

Related Vulnerabilities

Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-22457	Critical	9.0	100%	KEV + Ransom	Fix
CVE-2025-0282	Critical	9.0	100%	KEV + Ransom	-
CVE-2015-3113	Critical	9.8	100%	KEV	Fix
CVE-2021-20038	Critical	9.8	100%	KEV + Ransom	-
CVE-2023-4863	High	8.8	100%	KEV	Fix
CVE-2020-16040	Medium	6.5	100%	-	Fix

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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 2025-12-02.