CVE-2021-43523 Cross-site scripting in n/a

Critical 9.6 Published 10 Nov 2021 Updated 5 May 2025

Attackers can inject malicious content via DNS responses in uClibc, leading to remote code execution or XSS in applications using affected functions.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2021-43523?

CVE-2021-43523 is a critical cross-site scripting vulnerability in n/a, published on 10 Nov 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-79

Which versions are affected by CVE-2021-43523?

It affects 2 products.

Products include Uclibc-Ng Project Uclibc-Ng, Uclibc Uclibc.

How do I fix CVE-2021-43523?

Upgrade to a fixed version.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2021-43523 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-43523 exists.

Sources

Also known as AZL-6928, DEBIAN-CVE-2021-43523, GHSA-65xv-vmv6-8r3f.