Is CVE-2021-43523 in the CISA KEV catalog?

No. CVE-2021-43523 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-43523?

CVE-2021-43523 has a CVSS v3 base score of 9.6 (CRITICAL).

What is the EPSS score for CVE-2021-43523?

CVE-2021-43523 has an EPSS score of 3.26% (87th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-43523?

Upgrade uclibc-ng to 1.0.39 or later.

CVE & CISA-KEV Catalog

CVE-2021-43523

CRITICALEPSS 87th pctl

9.6

CVSS v3

NVD

Description

In uClibc and uClibc-ng before 1.0.39, incorrect handling of special characters in domain names returned by DNS servers via gethostbyname, getaddrinfo, gethostbyaddr, and getnameinfo can lead to output of wrong hostnames (leading to domain hijacking) or injection into applications (leading to remote code execution, XSS, applications crashes, etc.). In other words, a validation step, which is expected in any stub resolver, does not occur.

CWE-79Cross-Site Scripting (XSS)

How to fix

Remediation Available

uclibc-ngNVD

Affected:< 1.0.39Fixed in:1.0.39CVE-2021-43523derived from NVD

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 InteractionRequired

ScopeChanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

3.26%probability of exploitation in 30 days

87thpercentile

Elevated risk: more likely to be exploited than 87% of all known CVEs.

References

Patch1

github.com

Exploit1

openwall.com

Vendor Advisory1

uclibc-ng.org

Related Vulnerabilities

Other CWE-79 (Cross-Site Scripting (XSS)) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-11022	Medium	6.9	99%	-	Fix
CVE-2019-3929	Critical	9.8	99%	KEV	Fix
CVE-2020-9496	Medium	6.1	99%	-	-
CVE-2023-28341	Medium	6.1	99%	-	Fix
CVE-2018-12998	Medium	6.1	98%	-	-
CVE-2025-4123	High	7.6	98%	-	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 2025-05-05.