Talos Vulnerability Report

Summary

An exploitable privilege escalation vulnerability exists in the helper service of Clean My Mac X, version 4.04, due to improper input validation. An attacker with local access could exploit this vulnerability to modify the file system as root.

Tested Versions

Clean My Mac X 4.04

Product URLs

https://macpaw.com/cleanmymac

CVSSv3 Score

7.1 - CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

CWE

CWE-19: Improper Input Validation

Details

CleanMyMac X is an all-in-one cleanup and optimization tool for the Mac operating system. The application is able to scan the system and user directories, looking for unused and leftover files and applications. The applications also markets the ability to help detect and prevent viruses and malware on OS X. The software utilizes a privilege helper tool running as root to get this work done faster. This allows the application to remove and modify system files.

The vulnerability lies in the removeLaunchdAgentAtPath function of the helper protocol. The code for this function is:

user_input = objc_retain(a3);                                                                         [0]
v8 = objc_retain(v6);
objc_retain(CFSTR("/Library/LaunchDaemons/com.macpaw.CleanMyMac4.Agent.plist"));
if ( objc_msgSend(user_input, "isEqualToString:", CFSTR("/Library/LaunchDaemons/com.macpaw.CleanMyMac4.Agent.plist"), v5) )                                                           [1]
{
  v10 = objc_msgSend(&OBJC_CLASS___NSFileManager, "defaultManager");
  v11 = objc_retainAutoreleasedReturnValue(v10);
  objc_msgSend(
    v11,
    "removeItemAtPath:error:",
    CFSTR("/Library/PrivilegedHelperTools/com.macpaw.CleanMyMac4.Agent"),
    0LL);
  objc_release(v11);
  v12 = objc_msgSend(&OBJC_CLASS___NSFileManager, "defaultManager");
  v13 = objc_retainAutoreleasedReturnValue(v12);
  objc_msgSend(v13, "removeItemAtPath:error:", user_input, 0LL);
  objc_release(v13);
  exit(0);
}
v9 = +[CMLaunchdManager removeAgentAtPath:](&OBJC_CLASS___CMLaunchdManager, "removeAgentAtPath:", user_input); [2]

At location [0], the process grabs user input and stores it for later computation. Location [1] shows a check to see if the LaunchDAgent intended to be stopped is the Clean My Mac agent. If it is, it is deleted and the daemon exits. This daemon runs as root, so killing it arbitrarily crosses a privilege boundary. Again, at location [2], we see a call to removeAgentAtPath passing in the supplied user argument, thus removing the launched agent. There is no validation of the calling application, therefore, any application is able to access this function. This crosses a privilege boundary, allowing non-root users to delete a package’s privileged information.

Exploit Proof of Concept

Included with this advisory is an Xcode project, as well as a Python script. The Python script needs an administrator’s password to set up some root files on the system and exploit the vulnerability. The Xcode project contains the proof of concept.

Timeline

2018-11-20 - Vendor Disclosure
2018-12-27 - Vendor Patched
2019-01-02 - Public Release