The NetBSD qsort() function is recursive, and not randomized, an attacker can construct a pathological input array of N elements that causes qsort() to deterministically recurse N/4 times. This allows attackers to consume arbitrary amounts of stack memory and manipulate stack memory to assist in arbitrary code execution attacks. This affects NetBSD 7.1 and possibly earlier versions.

References

• https://nvd.nist.gov/vuln/detail/CVE-2017-1000378
• https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt
• http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/stdlib/qsort.c?rev=1.23&content-type=text/x-cvsweb-markup
• http://www.securityfocus.com/bid/99255