CVE-2020-27818: 
NixOS vulnerability analysis and mitigation

A flaw was discovered in the check_chunk_name() function of pngcheck-2.4.0, identified as CVE-2020-27818. The vulnerability was reported on October 27, 2020, affecting pngcheck, a tool used to verify the integrity of PNG, JNG and MNG files (CVE Mitre, NVD).

The vulnerability is a global buffer overflow in the check_chunk_name() function of pngcheck.c, which occurs due to improper use of casts. When processing a specially crafted PNG file, this can lead to an out-of-bounds read condition (Red Hat Bugzilla). The vulnerability has been assigned a CVSS score of 3.3 (Low), with attack vector being Local, attack complexity Low, and requiring user interaction (Ubuntu).

The impact of this vulnerability is considered low, as exploitation would likely only lead to a temporary denial of service through application crash. The vulnerability poses a low risk to application availability and requires the attacker to either have access to the victim's system or successfully convince a user to process a malicious file (Red Hat Bugzilla).

Exploitation of this vulnerability requires an attacker to either have access to the victim's system or use social engineering to convince a user to process a malicious PNG file. The attack requires local access and user interaction to be successful (Red Hat Bugzilla).

The primary mitigation is to avoid providing input files from untrusted sources to pngcheck. Various distributions have released patches to address this vulnerability, including Fedora, EPEL, Ubuntu, and Debian. Fixed versions have been released for multiple platforms including Fedora 31-34, EPEL 7/8, and Debian 9 (Red Hat Bugzilla, Debian LTS).