CVE-2021-43523

Name: CVE-2021-43523
Creator: NVD / NIST
Published: 2021-11-10T15:15:12.213+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.6/10EPSS 3.26%

Last modified Jun 17, 2026

CVE-2021-43523 is a critical-severity vulnerability rated 9.6/10 on the CVSS scale. 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.. EPSS estimates a 3.26% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.6/10

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

EPSS Probability

3.26%

86.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Uclibc	Uclibc	<= 0.9.33.2
Uclibc-Ng Project	Uclibc-Ng	< 1.0.39

References

https://github.com/wbx-github/uclibc-ng/commit/0f822af0445e5348ce7b7bd8ce1204244f31d174Patch, Third Party Advisory
https://uclibc-ng.org/Vendor Advisory
https://www.openwall.com/lists/oss-security/2021/11/09/1Exploit, Mailing List, Third Party Advisory
https://github.com/wbx-github/uclibc-ng/commit/0f822af0445e5348ce7b7bd8ce1204244f31d174Patch, Third Party Advisory
https://uclibc-ng.org/Vendor Advisory
https://www.openwall.com/lists/oss-security/2021/11/09/1Exploit, Mailing List, Third Party Advisory

Timeline

Published: Nov 10, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-43523?

How severe is CVE-2021-43523?

CVE-2021-43523 has a CVSS score of 9.6/10 (CRITICAL severity). The EPSS model estimates a 3.26% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43523?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-43523?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST