The freecon function frees up security-related resources that may be associated with SELinux or another access control system. If rbx points to a non-existent or already released resource, this can lead to security failures. The vulnerability could be that an attacker could try to manipulate the security context, which could lead to privilege escalation. To run this code, you can compile binary and run in shell:
g++ sudo_explit.cpp -o sudo_exploit
./sudo_exploit
P.S if you have a different path to the sudo x86 ELF binary, change args to your own version