Good day
Many IT professionals do
not know much about services, they know that it is an application that run in
background and able to run even without user login.
This is correct (as a
very basic definition), but there are more than this.
Today I will talk about
Windows Services.
Windows Services in
Windows Vista /7/ Server 2008 work in a different way that Windows XP and
Server 2003.
Here are some changes happened
to Windows Services:
-
SID: Each service had its own SID, so you can track the service
and set restriction on it. You can get the service SID by using the command sc
showsid “Service Name”.
The SID will be identical on all windows machine, this is because
the SID is generated using the service name, you can even know the SID for a
service that is no installed, try the same command but insted of w32time use any other name like "NoSuchName".
But How Windows know a SID for a non existing service??:
But How Windows know a SID for a non existing service??:
o
A Service SID is computed by taking the service’s UNICODE name
(all in upper case)
o
Run the result through SHA-1 hash
o
Add S-1-50-80- (always the service account start with S-1-50-80-)
-
Session 0: I will talk more about session 0 below
-
Protection: Windows Services are protected with System Integrity ,
Data Execution prevention, and registry virtualization disabled
Session 0:
When Windows XP Start,
the services are also started in the same session that the user use. Services
can interact with the user (showing message box – forms …).
In Windows Vista and
Server 2008, Windows Services are no longer using the same session; instead, they
are isolated in Session0. The first session is always for Windows Services. All
other user use session 1 or 2 …, no more direct interaction between users or
application and Windows Services. This will protect windows services from
attack like RPC attack, also all the services running in this session protected with
System integrity and DEP.
You may install old Windows software (for Windows XP) that install a service, and this service need to communicate with the user direct like displaying a message box, this service will fail to show the user the message box and the application will appear to be not responding for the user, as the service is waiting for user interaction in session0, but the user is in session1 and can not see the message box, so what you can do ??
If you want to be notified for any event in Session0, you can start a service named “Interactive Services Detection” ui0detect, this service will inform you for any request that generated from the service and need a user interaction. (enable and start this service if you are planning to use old software that using old services).
If you want to be notified for any event in Session0, you can start a service named “Interactive Services Detection” ui0detect, this service will inform you for any request that generated from the service and need a user interaction. (enable and start this service if you are planning to use old software that using old services).
So how services can
communicate with the user, simply the vendor need to recode their service to
use RPC, COM or Named pipes
Service Account:
All Windows Service need
to login. Most of Windows Vista are using the Local System account, This
account is so powerful, its like Windows administrator and can take full
control of the system.
Here are a list of
Service account that windows use:
Local System:
-
The Highest privilege account on a computer; has access to all
resources
-
Has no password
-
Access the network by using the computer account (PC$)
Network Service
-
Similar to limited users
-
Has no password
-
Access the network by using the computer accont
Local Service
-
Similar to limited user
-
Has no password
-
Access the network by using anonymous credential
Service Privileges and
permission:
There are a lot of
Windows Service running by default also when you install some application, they
create their own services, but the question is what privileges this service have ?
The answer is using SC
command “sc qprivs w32time” this command will list all the privileges
this service needs, in this case its W32Time.
But what if you want to give a service access to a local folder using NTFS permission ?
Dont forget that each service had its own SID, so you can add the service to any securable object. They can treated as a normal windows user but from another domain. Try the following:
Dont forget that each service had its own SID, so you can add the service to any securable object. They can treated as a normal windows user but from another domain. Try the following:
-
Create a new folder
-
Right click on the folder and select Properties
-
Go to Security and click add
-
Now write NT Services\w32time and press OK
-
You will notice that the service is listed as a user, and you can
give it the required permission like read access or write or whatever your
application need
Service Control (at the
root): its know that you can
control the service using the Serviecs.msc conosole or using the SC.exe
command, but if you want to make a look at the service root, then you will need
to use Windows registry
Open Windows Regedit and navigate to the following key HKLC\System\CurrentControlSet\Services,
here you will find all the services and the used windows driver, each key is a
service or a driver that hold several values in it:
ImagePath
|
The installation location of the service
|
RequiredPrivilege*
|
The privilege required by this service
|
ServiceSIDType*
|
The Type of the SID and it can be 0-1-2
|
Start
|
The startup type for the service
|
RequiredPrivilege: are the privileges this service will use, each services must declare what it will need to access, and if it try to access an undeclared privilege, it will fail.
I hope you find these information useful
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