Dccw.exe Uac Bypass

[Julia Dodoo]

Adversariesmay bypass UAC mechanisms to elevate process privileges on system. Windows User Account Control (UAC) allows a program to elevate its privileges (tracked as integrity levels ranging from low to high) to perform a task under administrator-level permissions, possibly by prompting the user for confirmation. The impact to the user ranges from denying the operation under high enforcement to allowing the user to perform the action if they are in the local administrators group and click through the prompt or allowing them to enter an administrator password to complete the action.[1]

If the UAC protection level of a computer is set to anything but the highest level, certain Windows programs can elevate privileges or execute some elevated Component Object Model objects without prompting the user through the UAC notification box.[2][3] An example of this is use of Rundll32 to load a specifically crafted DLL which loads an auto-elevated Component Object Model object and performs a file operation in a protected directory which would typically require elevated access. Malicious software may also be injected into a trusted process to gain elevated privileges without prompting a user.[4]

Many methods have been discovered to bypass UAC. The Github readme page for UACME contains an extensive list of methods[5] that have been discovered and implemented, but may not be a comprehensive list of bypasses. Additional bypass methods are regularly discovered and some used in the wild, such as:

Another bypass is possible through some lateral movement techniques if credentials for an account with administrator privileges are known, since UAC is a single system security mechanism, and the privilege or integrity of a process running on one system will be unknown on remote systems and default to high integrity.[8]

BitPaymer can suppress UAC prompts by setting the HKCU\Software\Classes\ms-settings\shell\open\command registry key on Windows 10 or HKCU\Software\Classes\mscfile\shell\open\command on Windows 7 and launching the eventvwr.msc process, which launches BitPaymer with elevated privileges.[16]

Although UAC bypass techniques exist, it is still prudent to use the highest enforcement level for UAC when possible and mitigate bypass opportunities that exist with techniques such as DLL Search Order Hijacking.

Threat actors often, after compromising a machine, try to disable User Access Control (UAC) to escalate privileges. This is often done by changing the registry key for system policies using "reg.exe", a legitimate tool provided by Microsoft for modifying the registry via command prompt or scripts. This action interferes with UAC and may enable a threat actor to escalate privileges on the compromised system, thereby allowing further exploitation of the system.

Monitor contextual data about a running process, which may include information such as environment variables, image name, user/owner that may bypass UAC mechanisms to elevate process privileges on system.

Some UAC bypass methods rely on modifying specific, user-accessible Registry settings. For example:* The eventvwr.exe bypass uses the [HKEY_CURRENT_USER]\Software\Classes\mscfile\shell\open\command Registry key.[6]* The sdclt.exe bypass uses the [HKEY_CURRENT_USER]\Software\Microsoft\Windows\CurrentVersion\App Paths\control.exe and [HKEY_CURRENT_USER]\Software\Classes\exefile\shell\runas\command\isolatedCommand Registry keys.[68][69]Analysts should monitor these Registry settings for unauthorized changes.

UAC Bypass is an interesting technique in that new implementations are regularly found and existing implementations may be fixed (i.e., patched) by Microsoft in new builds of Windows. Therefore, it is important to validate than detections for UAC Bypass are still relevant (i.e., they target non-patched implementations).

Note: Sysmon Event ID 12 (Registry Key Create/Delete), Sysmon Event ID 13 (Registry Value Set), and Sysmon Event ID 14 (Registry Key and Value Rename) are useful for creating detections around Registry Key Modification in the context of UAC Bypass.

Windows User Account Control (UAC) permits a program to elevate its privileges to execute a task under administrator-level permissions. If the UAC protection of a computer is set to the default level, the user will be prompted through a notification box to confirm the elevation request change. In many cases, however, Windows programs can elevate privileges or execute tasks without prompting the user for confirmation. Cyber criminals abuse those mechanisms to run their malware with administrative privileges without the user prompt, achieving UAC bypasses.

This method works by abusing a Windows Side-By-Side (WinSxS) DLL loading issue and an auto-elevated IFileOperation COM Object. When those auto-elevated binaries search for a WinSxS library, they first search inside a .local folder, which are used legitimately for library redirection by developers.

Often, the .local folder doesn't exist, so if an attacker can create that folder and the targeted library before the auto-elevated binary runs, he can set up a malicious DLL to be loaded inside the auto-elevated binary. This is a form of DLL Hijack.

Cortex XDR provides extensive coverage against UAC bypass attacks. The platform stops threats on endpoints and coordinates enforcement with network and cloud security to prevent successful cyber attacks. To prevent the exploitation of UAC Bypasses, the Behavioral Threat Protection (BTP) and Local Analysis Protection modules in Cortex XDR monitor for malicious behaviors across a sequence of events and immediately terminate the attack when detected.

Our business network is set up via GP to disallow our users to install software/updates/etc on their computers. However, we have one application that has to update on the 1st and 15th of each month, and currently requires us to remote in, punch in our credentials, and initiate the update for the user.

Googling has revealed that UAC can be disabled for particular applications via Task Scheduler, Microsoft Application Compatibility Toolkit, or third-party apps, but those use-cases are when credentials are not required. In your experience do those also work when credentials are required? Which would you recommend, and/or how have you gotten around this in your own organizations? Can this be centrally managed/deployed with a script/application/etc. without having to make edits to each computer?

The Microsoft Application Compatibility Toolkit is what my company uses for a certain program we have. This program requires admin privileges to do certain things and this program essentially bypasses it without requiring us to give admin privileges to the user.

DLL Hijacking is a popular technique for executing malicious payloads. This post lists nearly 300 executables vulnerable to relative path DLL Hijacking on Windows 10 (1909), and shows how with a few lines of VBScript some of the DLL hijacks can be executed with elevated privileges, bypassing UAC.

Attackers have been seen to use DLL hijacking in different ways and for different reasons. Motives include execution (executing malicious code through a trusted executable may be less likely to set off alarm bells, and in some cases even bypasses application whitelist features such as AppLocker [1]), obtaining persistence (if the target application is pre-installed and runs regularly, so will the malicious code) and privilege escalation (if the target application runs under elevated permissions, so will the malicious code).

The biggest challenge is to find a vulnerable executable that can be exploited under default user permissions. When targeting pre-installed system executables on Windows, that typically excludes the first option, whilst any folders eligible in options 2 and 3 have to be user writeable, as should the the files and folder in options 4 and 5. This is usually not the case.

To prevent new versions of this technique to be successful, it is worthwhile identifying executables that are vulnerable to this kind of DLL hijacking. This will provide red teamers with new means for execution, but more importantly, it will allow threat hunters and defenders to take appropriate measures to detect and prevent.

This allows us to identify all DLLs queried by each application, which will be all potential hijackable DLL candidates. But it does not automatically follow that all of these are also loaded (and therefore executed). The most reliable way to find out which DLLs are properly loaded, is to compile our own version of the DLL, and make it write to a unique file upon successfully loading. If we then repeat the above approach for all target executables and DLLs, it will result in a collection of files that tells us which DLLs are confirmed vulnerable to DLL hijacking.

Compiling custom versions of existing DLLs is more challenging than it may sound, as a lot of executables will not load such DLLs if procedures or entry points are missing. Tools such as DLL Export Viewer [13] can be used to enumerate all external function names and ordinals of the legitimate DLLs. Ensuring that our compiled DLL follows the same format will maximise the chances of it being loaded successfully.

Having found all these executables, at most this allows us to execute code through trusted programs. However, it is also possible to gain elevated rights if used in conjunction with UAC Bypass techniques.

User Account Control (UAC) [16] was introduced in Windows Vista as a security feature, asking users for confirmation through a prompt before a process running under normal privileges is elevated to higher privileges. After users complained about getting flooded with UAC prompts when doing arbitrary tasks, Microsoft introduced auto elevation in Windows 7, which automatically elevates certain processes if they are located in trusted directories (such as c:\windows\system32 ).

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