In part 3 of this AppLocker series, we will go through the rules that AppLocker uses to allow or block specific applications. Firstly, note that explicitly defined Block rules (non generic) override any Allow rules (generic). Secondly, note that if you don’t set a default policy to allow all applications, then any application that has no Allow policy will not be allowed to execute. When creating rules you can take two different approaches, either you allow all applications to run with specific ones set as blocked, or leave the default behavior of AppLocker and then allow specific applications to run (remember to allow administrators full allow permissions and everyone to run system applications). However, it is recommended to start implementing AppLocker rules by performing an audit exercise prior to the actual enforcement of rules.
Unlike the Software Restrictions Policies, the AppLocker Application Control Policies are available only in Windows 7 Enterprise and Ultimate editions, and all editions of Windows Server 2008 R2. AppLocker policies build upon the Software Restriction Polices functionality but have additional features which make them far more powerful and useful. One of the main enhancements is the ability to specify which users can run specific applications. Now, rules can be based on file attributes such as, file name, file version, etc. You can create exceptions to rules and assign a rule to a security group or an individual user. The various added features are audit-only mode, policy import and export, rule collection, PowerShell support, custom error messages and a wizard to create multiple rules at once. The Policies are found in the Computer Configuration\Windows Settings\Security Settings\Application Control Policies node.
The first caution worth noting is when you are upgrading computers to Windows 7 with enabled Software Restriction Policies. If you implement AppLocker policies to the upgraded computer, then only the AppLocker rules are enforced. Secondly, AppLocker depends on the Application Identity Service which is set to a Manual startup state by default. Before setting the service to start automatically make sure that the policies are correctly set as incorrect rules may turn your computer unusable. Finally, keep in mind that when DLL rules are used users may experience a reduction in performance as AppLocker checks DLLs when the application is loading.
Creating Default Rules