UAC - User Account Control
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User Account Control (UAC) is a feature that enables a consent prompt for elevated activities. Applications have different integrity levels, and a program with a high level can perform tasks that could potentially compromise the system. When UAC is enabled, applications and tasks always run under the security context of a non-administrator account unless an administrator explicitly authorizes these applications/tasks to have administrator-level access to the system to run. It is a convenience feature that protects administrators from unintended changes but is not considered a security boundary.
For more info about integrity levels:
Integrity LevelsWhen UAC is in place, an administrator user is given 2 tokens: a standard user key, to perform regular actions as regular level, and one with the admin privileges.
This page discusses how UAC works in great depth and includes the logon process, user experience, and UAC architecture. Administrators can use security policies to configure how UAC works specific to their organization at the local level (using secpol.msc), or configured and pushed out via Group Policy Objects (GPO) in an Active Directory domain environment. The various settings are discussed in detail here. There are 10 Group Policy settings that can be set for UAC. The following table provides additional detail:
| Group Policy Setting | Registry Key | Default Setting |
|---|---|---|
FilterAdministratorToken | Disabled | |
EnableUIADesktopToggle | Disabled | |
ConsentPromptBehaviorAdmin | Prompt for consent for non-Windows binaries | |
ConsentPromptBehaviorUser | Prompt for credentials on the secure desktop | |
EnableInstallerDetection | Enabled (default for home) Disabled (default for enterprise) | |
ValidateAdminCodeSignatures | Disabled | |
EnableSecureUIAPaths | Enabled | |
EnableLUA | Enabled | |
PromptOnSecureDesktop | Enabled | |
EnableVirtualization | Enabled |
Some programs are autoelevated automatically if the user belongs to the administrator group. These binaries have inside their Manifests the autoElevate option with value True. The binary has to be signed by Microsoft also.
Then, to bypass the UAC (elevate from medium integrity level to high) some attackers use this kind of binaries to execute arbitrary code because it will be executed from a High level integrity process.
You can check the Manifest of a binary using the tool sigcheck.exe from Sysinternals. And you can see the integrity level of the processes using Process Explorer or Process Monitor (of Sysinternals).
To confirm if UAC is enabled do:
If it's 1 then UAC is activated, if its 0 or it doesn't exist, then UAC is inactive.
Then, check which level is configured:
If 0 then, UAC won't prompt (like disabled)
If 1 the admin is asked for username and password to execute the binary with high rights (on Secure Desktop)
If 2 (Always notify me) UAC will always ask for confirmation to the administrator when he tries to execute something with high privileges (on Secure Desktop)
If 3 like 1 but not necessary on Secure Desktop
If 4 like 2 but not necessary on Secure Desktop
if 5(default) it will ask the administrator to confirm to run non Windows binaries with high privileges
Then, you have to take a look at the value of LocalAccountTokenFilterPolicy
If the value is 0, then, only the RID 500 user (built-in Administrator) is able to perform admin tasks without UAC, and if its 1, all accounts inside "Administrators" group can do them.
And, finally take a look at the value of the key FilterAdministratorToken
If 0(default), the built-in Administrator account can do remote administration tasks and if 1 the built-in account Administrator cannot do remote administration tasks, unless LocalAccountTokenFilterPolicy is set to 1.
If EnableLUA=0 or doesn't exist, no UAC for anyone
If EnableLua=1 and LocalAccountTokenFilterPolicy=1 , No UAC for anyone
If EnableLua=1 and LocalAccountTokenFilterPolicy=0 and FilterAdministratorToken=0, No UAC for RID 500 (Built-in Administrator)
If EnableLua=1 and LocalAccountTokenFilterPolicy=0 and FilterAdministratorToken=1, UAC for everyone
All this information can be gathered using the metasploit module: post/windows/gather/win_privs
You can also check the groups of your user and get the integrity level:
Note that if you have graphical access to the victim, UAC bypass is straight forward as you can simply click on "Yes" when the UAC prompt appears
The UAC bypass is needed in the following situation: the UAC is activated, your process is running in a medium integrity context, and your user belongs to the administrators group.
It is important to mention that it is much harder to bypass the UAC if it is in the highest security level (Always) than if it is in any of the other levels (Default).
If UAC is already disabled (ConsentPromptBehaviorAdmin is 0) you can execute a reverse shell with admin privileges (high integrity level) using something like:
If you have a shell with a user that is inside the Administrators group you can mount the C$ shared via SMB (file system) local in a new disk and you will have access to everything inside the file system (even Administrator home folder).
Looks like this trick isn't working anymore
The Cobalt Strike techniques will only work if UAC is not set at it's max security level
Empire and Metasploit also have several modules to bypass the UAC.
Documentation and tool in https://github.com/wh0amitz/KRBUACBypass
UACME which is a compilation of several UAC bypass exploits. Note that you will need to compile UACME using visual studio or msbuild. The compilation will create several executables (like Source\Akagi\outout\x64\Debug\Akagi.exe) , you will need to know which one you need.
You should be careful because some bypasses will prompt some other programs that will alert the user that something is happening.
UACME has the build version from which each technique started working. You can search for a technique affecting your versions:
Also, using this page you get the Windows release 1607 from the build versions.
All the techniques used here to bypass AUC require a full interactive shell with the victim (a common nc.exe shell is not enough).
You can get using a meterpreter session. Migrate to a process that has the Session value equals to 1:
(explorer.exe should works)
If you have access to a GUI you can just accept the UAC prompt when you get it, you don't really need a bypass it. So, getting access to a GUI will allow you to bypass the UAC.
Moreover, if you get a GUI session that someone was using (potentially via RDP) there are some tools that will be running as administrator from where you could run a cmd for example as admin directly without being prompted again by UAC like https://github.com/oski02/UAC-GUI-Bypass-appverif. This might be a bit more stealthy.
If you don't care about being noisy you could always run something like https://github.com/Chainski/ForceAdmin that ask to elevate permissions until the user does accepts it.
If you take a look to UACME you will note that most UAC bypasses abuse a Dll Hijacking vulnerability (mainly writing the malicious dll on C:\Windows\System32). Read this to learn how to find a Dll Hijacking vulnerability.
Find a binary that will autoelevate (check that when it is executed it runs in a high integrity level).
With procmon find "NAME NOT FOUND" events that can be vulnerable to DLL Hijacking.
You probably will need to write the DLL inside some protected paths (like C:\Windows\System32) were you don't have writing permissions. You can bypass this using:
wusa.exe: Windows 7,8 and 8.1. It allows to extract the content of a CAB file inside protected paths (because this tool is executed from a high integrity level).
IFileOperation: Windows 10.
Prepare a script to copy your DLL inside the protected path and execute the vulnerable and autoelevated binary.
Consists on watching if an autoElevated binary tries to read from the registry the name/path of a binary or command to be executed (this is more interesting if the binary searches this information inside the HKCU).
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