![]() Bypassing Windows User Account Control (UAC) and ways of mitigation. Securing machines from abuse and compromise in a corporate environment has always been an ongoing process. Providing admin rights to users has always been abused as users have ended up installing unapproved software, change configurations, etc. Not giving local admin rights and they claim they can’t do their work. Windows XP shutdown issues mostly center around a very few issues, especially legacy hardware and software compatibility issues. Currently, the leading cause of. GridinSoft Anti-Malware - GridinSoft Anti-Malware effectively targets PC threats, including adware, malware, and PUPs allowing you to purge them with ease - ensuring. Important Information for Windows Vista or 7 and Windows 7 Users. For users that have Windows Vista or 7, it will be important that you understand. If malware happens to compromise the machine with full admin rights then you are most likely looking at reimaging the machine. User Account Control (UAC) gives us the ability to run in standard user rights instead of full administrator rights. So even if your standard user account is in the local admin group damage is limited, i. To carry out these actions users would need to interact with the desktop such us right click and run as administrator or accept the UAC elevation prompt. UAC was introduced from Windows Vista onwards and contains a number of technologies that include file system and registry virtualization, the Protected Administrator (PA) account, UAC elevation prompts and Windows Integrity levels. UAC works by adjusting the permission level of our user account, so programs actions are carried out as a standard user even if we have local admin rights on the computer. When changes are going to be made that require administrator- level permission UAC notifies us. If we have local admin rights then we can click yes to continue otherwise we would be prompted to enter an administrator password. These would however depend on what policies have been defined in your environment. This blog post shows how easily UAC elevation prompts could be bypassed and what actions could be taken to mitigate this threat. Bypassing UACExploiting UAC is a trivial process. ![]() There are two stages needed to be taken to achieve bypass to elevate from standard user rights to administrator user rights. These steps have widely been published so it’s nothing new though stage 2 documents some more DLL hijacking vulnerabilities. Writing to a secure location. Exploiting DLL hijacking vulnerability. In order for our bypass to be successful to start off with we need. A medium integrity process. A standard user in an administrators group. Windows executable must be signed by Microsoft code signing certificate. Windows executable must be located in a secure directory. Windows executable also must specify the auto Elevate property in their manifest. ![]() The DEP Data Execution Prevention is a security feature that has been available since Windows XP SP2. You will also find this feature in Windows 7, 8 or.Writing to a secure location. There are a couple of ways we can write to a secure location. Using the IFile. Operation COM Object. Using Windows Update Standalone Installer (wusa. IFile. Operation COM Object. The IFile. Operation COM object has a method that we can use to copy files to our secure location as the operation will auto- elevate and able to do a privilege copy. To exploit we can in inject our malicious DLL in a medium integrity process to carry out the operation. ![]() Since the COM object is set to auto- elevate the injected process does not need to be marked for auto- elevation in its manifest. On windows 7 injected processes that have copied successfully are. C: \Windows\explorer. C: \Windows\System. C: \Windows\System. During tests taskhost. On Windows 8 injected processes that have copied successfully are. C: \Windows\explorer. C: \Windows\System. C: \Windows\System. Runtime. Broker. exe. Again explorer. exe is only the reliable process to use I found during my tests and the only one that worked on Windows 8. The main part of the code below has been taken from MSDN with just the some minor changes. The Set. Operation. Flags values used was taken from the UAC bypass code published here.#include < stdio. Shobjidl. h>. #include < Windows. ![]() What is DEP? In Microsoft’s own words, Data Execution Prevention (DEP) is a security feature that can help prevent damage to your computer from viruses an. In computing, the 3 GB barrier . It prevents the operating. Complete set of content formerly published at Windows TechNet for Windows Server 2003, Server 2003 Service Pack 1 and 2, and Windows Server 2003 R2. This is just a short post highlighting how easily ASLR could be bypassed by instantiating ActiveX controls using certain classids in Microsoft Office. Wusa. exe when executed runs as a high integrity process as its set to auto- elevate in its manifest. For auto- elevation the Windows executable must be signed, located in a secure directory such as C: \Windows\System. Elevate property in their manifest. We use wusa. exe to extract a CAB file (cabinet archive file) to our secure locationwusa c: \users\user. Here in the example our cab file is called poc. Windows comes with the makecab. CRYPTBASE. dll c: \users\user. Exploiting DLL hijacking vulnerability. When exploiting a DLL hijacking vulnerability the executable we are going to run again has to be signed; located in a secure directory and must specify the auto. Elevate property in its manifest in order load as a high integrity process. On Windows 7 there are three executables that could be exploited and associated DLLs listed below. C: \windows\ehome\Mcx. Prov. exe. C: \Windows\ehome\CRYPTBASE. C: \windows\System. C: \Windows\System. CRYPTSP. dll. C: \windows\System. CRYPTBASE. dll. C: \Windows\System. Rpc. Rt. Remote. dll. C: \Windows\System. Ux. Theme. dll. C: \windows\System. C: \Windows\System. NTWDBLIB. DLLOn malwr. June last year had already been using Mcx. Prov. exe to bypass UAC and day later an exploit had also been published. The same hash had also been flagged on Virus. Total (3. 8/5. 4) submitted over four months ago. On Windows 8 there are also three executables that could be exploited and associated DLLs listed below. C: \windows\System. C: \windows\System. CRYPTBASE. dll. C: \Windows\System. Sysprep\dwmapi. dll. C: \Windows\System. Sysprep\SHCORE. dll. C: \windows\System. C: \Windows\System. NTWDBLIB. DLL. C: \windows\System. C: \Windows\System. C: \Windows\System. URe. FS. DLLFinally on Windows 8. DLLs listed below. C: \windows\System. C: \Windows\System. Sysprep\SHCORE. dll. C: \Windows\System. Sysprep\OLEACC. DLL. C: \windows\System. C: \Windows\System. NTWDBLIB. DLL. C: \windows\System. C: \Windows\System. C: \Program Files\Common Files\microsoft shared\ink\CRYPTBASE. C: \Program Files\Common Files\microsoft shared\ink\CRYPTSP. C: \Program Files\Common Files\microsoft shared\ink\dwmapi. C: \Program Files\Common Files\microsoft shared\ink\USERENV. C: \Program Files\Common Files\microsoft shared\ink\OLEACC. Calling pwcreator. Create a Windows To Go workspace) executable calls vds. Virtual Disk Service) which then loads our DLL and gives us System integrity running in SYSTEM account. Calling these executables sysprep. GUI window but should be able to easily make it run in the background and then terminated after being exploited. This is something I haven’t looked into so I’ll leave upto you. Mitigation. The best way to mitigate this bypass is just by not giving users local admin rights to their machines. Majority of user accounts in a corporate environment you should be able to do this reducing the attack surface. This however does not apply home users which would have local admin rights by default. The actual bypass only works when set to the middle two UAC settings which will let it auto- elevate. To see your settings you need to go to Control Panel – User Accounts – Change User Account Control settings. Notify me only when apps try to make changes to my computer (default) Notify me only when apps try to make changes to my computer (do not dim desktop settings)so we could set to Always notify but this would bring it back to like it was on Windows Vista with constant notifications and not really practical and the user would end up setting it to Never notify which is definitely not a good idea. Microsoft has given us 1. UAC policies to play with so it’s worth spending some time understanding and testing these out before implementing it in your own domain environment. To see what is applied on your local machine type secpol. Start- Run to open the Local Security Policy snap- in and expand the Local Policies- Security Options folder. Run rsop. msc to view group policies applied on machines in a domain environment. Looking in the registry these are the default values of UAC. This is an extremely dangerous value to be in and should never be disabled so its strongly recommend to set this settings to be enabled in group policies so it always gets applied if settings are reset/changed by users or by previously removed malware. User Account Control: Run all administrators in Admin Approval Mode. Once disabled not only a malicious process could be able to go straight to high integrity without any bypass but also Internet Explorer would run in medium integrity. UAC gives us the Protected Mode (sandbox) in Internet Explorer providing added security. Internet Explorer normally runs in low integrity child process so if compromised by some IE exploit the damage is minimized as in low integrity there are only a handful of locations it can be written to on the system. These changes mentioned above have been seen on Windows 7. On Windows 8/8. 1 Enable. LUA does not change to disabled. So when the slider is moved to Never notify the values changed are only. This applies to Windows 7/8 and 8. DO NOT logon using local admin account, if local admin rights are required better add their domain account to the local administrators group. If for whatever reason logging on using the local admin account is a necessity then best set this UAC policy to enabled. User Account Control: Admin Approval Mode for the built- in Administrator account“Filter. Administrator. Token”=dword: 0. Another option would be to look into renaming or deleting the executables Mcx. Prov. exe, sysprep. DLL hijacking fails. Finally if users do require local admin privileges then worth setting their machine UAC policy to Always notify and they live with the constant notifications. User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode (2- Prompt for consent on the secure desktop)Conclusion. This bypass only works when all of the requirements are available to abuse. Remove one requirement and the bypass will fail. Office documents are opened in medium integrity so these are ideal targets to abuse the UAC bypass. Since these bypasses are so effortlessly achieved the only real course of action would be to set UAC to “Always notify” or remove local admin rights for the user. In the end using agents like Microsoft EMET or Malware.
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