CVE-2021-21871: 
PowerISO vulnerability analysis and mitigation

A memory corruption vulnerability (CVE-2021-21871) was discovered in PowerISO 7.9's DMG File Format Handler functionality. The vulnerability was discovered by Piotr Bania of Cisco Talos and publicly disclosed on June 28, 2021, after being reported to the vendor on June 5, 2021. The vulnerability affects PowerISO version 7.9, a CD/DVD/BD image file processing tool that provides support for Apple Disk Image (DMG) file format (Talos Report).

The vulnerability is classified as an out-of-bounds write (CWE-787) with a CVSSv3 score of 8.8 (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H). The issue occurs when PowerISO inflates ZLIB sections within DMG files, where it fails to correctly check the boundary of the output buffer. When processing a specifically crafted DMG file with a malformed ZLIB section, it's possible to trigger memory corruption through malformed DIST or DISTEX codes in the ZLIB bytecode (Talos Report).

A successful exploitation of this vulnerability could lead to memory corruption, potentially allowing an attacker to execute arbitrary code on the victim's machine. The high CVSS score of 8.8 indicates severe potential impacts on system confidentiality, integrity, and availability (Talos Report).

The vulnerability can be exploited by tricking a user into opening a specially crafted DMG file. The attack requires user interaction but does not require authentication, making it relatively easy to exploit given successful social engineering. Cisco Talos has released SNORT rules 57728 and 57729 to detect exploitation attempts (Talos Blog).

The vendor has fixed this vulnerability in a bug-release of PowerISO version 7.9. Users should ensure they are running PowerISO version 7.9 with the most recent bug fixes, although the version number remained unchanged in the fixed release (Talos Report).