CRITICAL

CVE-2021-43523

Q: What is CVE-2021-43523?

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.

Q: Is CVE-2021-43523 actively exploited?

Active exploitation of CVE-2021-43523 has not been confirmed. Its EPSS score was 3.1% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-43523?

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

CVSS v3

9.6

CRITICAL

EPSS Score

3.1 %

exploit probability, as of 2026-10-19

CISA KEV

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

CVE-2021-43523 Red Hat Product Security
uclibc: incorrect handling of special characters in DNS records
ICSA-23-234-01 CISA1 known affected
Hitachi Energy AFF66x
AFF660/665: <= 03.0.02

Full record on 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.

Technical details

Published: 2021-11-10

Frequently asked questions

What is CVE-2021-43523?

Is CVE-2021-43523 actively exploited?

Active exploitation of CVE-2021-43523 has not been confirmed. Its EPSS score was 3.1% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

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

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

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