The OpenBSD 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 OpenBSD 6.1 and possibly earlier versions.
https://www.exploit-db.com/exploits/42271/
https://support.apple.com/HT208144
https://support.apple.com/HT208115
https://support.apple.com/HT208113
https://support.apple.com/HT208112