CVE-2021-33643: 
NixOS vulnerability analysis and mitigation

CVE-2021-33643 is a security vulnerability in libtar, a C library for manipulating tar archives. The vulnerability was discovered and disclosed in May 2021. The issue affects the libtar package, which supports both the strict POSIX tar format and many commonly-used GNU extensions. This vulnerability occurs when processing specially crafted tar files (CVE MITRE).

The vulnerability is triggered when an attacker submits a crafted tar file with size in header struct being 0, which can cause a calling of malloc(0) for a variable gnu_longlink, resulting in an out-of-bounds read condition. This technical issue affects the tar file processing functionality of the library (NVD).

The vulnerability can lead to an out-of-bounds read condition when processing specially crafted tar files. This could potentially allow attackers to access memory outside of intended boundaries, which could lead to information disclosure or program crashes (Red Hat CVE).

The vulnerability can be exploited by submitting a specially crafted tar file with specific header structure modifications. The exploitation requires the attacker to be able to supply a malicious tar file to a system using the affected libtar library (Debian Security).

Multiple vendors have released patches to address this vulnerability. Red Hat has released security updates for affected versions in RHEL 8. Fedora has also provided fixes in versions 1.2.20-25 and later for affected releases. Users are advised to update to the patched versions of libtar (Fedora Update, Red Hat Advisory).