For what purpose(s) is the SeTcbPrivilege privilege in Windows used? Can it be used, for example, to run a program under the SYSTEM account?
Acting as a part of the operating system allows you to do things like create login tokens. It's unlikely that you would ever need to write a service that uses this privilege unless you're writing an authentication provider.
Since you can create access tokens, you can act as any user. Of course, this means that you can run programs under the SYSTEM account, but there are much easier ways to run something as SYSTEM.
To add to Gabe's answer, here is what MS says,
Allows a process to assume the identity of any user and thus gain
access to the resources that the user is authorized to access.
Typically, only low-level authentication services require this
privilege.
Default setting: Not assigned.
Note that potential access is not limited to what is associated with
the user by default; the calling process might request that arbitrary
additional privileges be added to the access token. The calling
process might also build an access token that does not provide a
primary identity for tracking events in the audit log.
When a service requires this privilege, configure the service to log
on using the Local System account, which has the privilege inherently.
Do not create a separate account and assign the privilege to it.
Source: Microsoft TechNet
SeTcbPrivilege is very useful for debugging purpose. For example, if you are developing Windows service that has to be run under system account and perform impersonate things it is conveniently to run this service as standalone exe. SeTcbPrivilege will allow to do this.
Related
I'm trying to create a Windows service that has the right to create additional services. But I'd prefer not to make this service run with an Administrative login.
The users rights are otherwise quite limited - I just need it to be able to spin-up a service on request.
I've seen mention online that SC_MANAGER_CREATE_SERVICE is a permission you can now assign and/or change, but I haven't seen much on how that is done. There is mention of being able to change permissions for individual services via subinacl, via OpenSCManager and the - gulp - sc command. But these examples show how to change the permissions on a single service, not how to give a user SC_MANAGER_CREATE_SERVICE permissions.
However, I've noticed that the documentation on CreateService specifically says that it requires administrator privilages - so perhaps it's simply not possible.
Am I going to have to start the service with an admin account? Or does anyone know another trick?
See Service Security and Access Rights:
To get or set the security descriptor for the SCM, use the QueryServiceObjectSecurity and SetServiceObjectSecurity functions with a handle to the SCManager object.
Be aware that having the right to create services gives you effective administrator access, since you can create a service to run as local system. So you do need to be careful not to grant that right to accounts that untrusted users have access to, to make sure that all accounts with that right have strong passwords, and so on.
This also means that if your system service is compromised by a remote code execution vulnerability you haven't gained anything, the attacker will still be able to get control of your system. If the service is at a high risk of direct attack, it may be wise to instead have a second service that is responsible only for the tasks that require special privilege. However, for a service that is unlikely to be directly attacked, or is considered reasonably secure, running without administrator privileges (other than the ability to create services) may prevent a less severe vulnerability from being exploitable, or limit the damage caused by a non-security-related bug.
See also Granting service control manager access permission to user outside of administrator group on Server Fault, the answer shows how to change the SCM permissions from the command line.
Try opening an handle to the service control manager with the WRITE_DAC access right, and change the security of it by calling SetServiceObjectSecurity to change the dacl of the service control manager. Don't forget to do the same thing for the service registry key (HKLM\SYSTEM\CurrentControlSet\Services) using RegOpenKeyEx and RegSetKeySecurity function.
WARNING
Be aware that this is a potential security risk since it would allow a standard user account to elevate its privileges to SYSTEM.
Is it possible to grant a user a specific privilege, but then restrict the use of that privilege to a specific list of applications? For example, lets say that I have a special debugging application that I want use on a normal account that requires the SeDebugPrivilege to be enabled to work. However, I want every application other than the aforementioned debugger running under the normal account to be restricted from using this privilege. Is this possible? If so, how can this be done programmatically?
We have developed a ASP.NET 3.5 web application with Web Server 2008 and has implemented a custom authentication solution using active directory as the credentials store. Our front end application uses a normal login form to capture the user name and password and leverages the Win32 LogonUser method to authenticate the user’s credentials. When we are calling the LogonUser method, we are using the LOGON32_LOGON_NETWORK as the logon type.
The issue we have found is that user profile folders are being created under the C:\Users folder of the web server. The folder seems to be created when a new user who has never logged on before is logging in for the first time. As the number of new users logging into the application grows, disk space is shrinking due to the large number of new user folders getting created.
I need to get the token back after the authentication (authenticated \ password locked \ wrong password ) its futher use and based on logic showing different web pages
Has anyone seen this behavior with the Win32 LogonUser method?
Please answer the following issue:
Is it possible to disable this behavior to create the folder as taking 2.78 MB of space for every new user and it eating my disck space?
I have tried LOGON32_LOGON_BATCH but it was giving an error 1385 in authentication user.
For any solution related to LOGON32_LOGON_BATCH, can you please confirm if that will stop creating the folders at location C:\users.
Also for any possible solution I need either
I am able to disable the folder to be created at C:\user or
Any other option to authenticated user which will not creat folders.
Pass LOGON32_LOGON_BATCH and grant the users permission to log on as a batch job on that machine using Group Policy.
The MSDN documentation for LogonUser recommends LOGON32_LOGON_BATCH as the logon type for web services:
This logon type is intended for batch
servers, where processes may be
executing on behalf of a user without
their direct intervention. This type
is also for higher performance servers
that process many plaintext
authentication attempts at a time,
such as mail or Web servers. The
LogonUser function does not cache
credentials for this logon type.
Have you tried that?
You don't write any information about the version of products (.NET, Windows Server which you use) and the best answer on your question can depend on this. Moreover the best way for your solution depend on what you want to do with the users token after logon. Do you really want to use this token or you want only verify the user? So I try to answer most general on your question.
In general, error 1385 (ERROR_LOGON_TYPE_NOT_GRANTED) means following (see http://support.microsoft.com/kb/155012/en):
A user has requested a type of logon,
such as interactive or network, that
was not granted. An administrator has
control over who may logon
interactively and through the network.
There are SE_BATCH_LOGON_NAME and SE_DENY_BATCH_LOGON_NAME (NTSecAPI.h) privileges which can be disabled/enabled in your case (see http://msdn.microsoft.com/en-us/library/bb545671%28VS.85%29.aspx for description). Use Process Explorer started with administrator rights (see http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx) to see which privileges has a process and which from there are enabled (see "Security" tab of a process). If your account used for the application pool don't have SE_BATCH_LOGON_NAME granted or this privilege is not enabled before call of LogonUser, you should add the corresponding code in your program.
By the way sometimes you don't really want to do much with an user account and want only verify a password. To do this you can use an old way with SSPI (see http://support.microsoft.com/kb/180548/en) which are used inside of LogonUser implementation. This way is the most smart and quick way to verify an user account which I know.
You can look at "The SSPI Workaround" (see http://alt.pluralsight.com/wiki/default.aspx/Keith.GuideBook/HowToGetATokenForAUser.html) for more information of usage SSPI in .NET 2.0.
I am trying to find out the difference between difference service account types. I tumbled upon this question.
The answer was because it has powerful access to local resources, and Network Service should be used if possible.
But still I am not able to understand that if it has powerful access to local resources, how attacker can access the account? What are the ways to compromise the account? I understood it is all about security, but I don't know how. It could be dark hacker's world, however anybody could explain, in simple terms, why network service account is better than local account ?
Thanks in advance.
Every program you run increases the attack surface of your server.
You have to assume that a determined, malicious actor can exploit bugs or loopholes in your program to make it do anything. You mitigate that by executing your programs with the least privileges required to do their jobs.
Some of these exploits include:
Luring attacks, in which an attacker tricks your program into executing their code under the program's elevated privileges.
Buffer Overrun Attacks, in which extra data sent to a method is written into adjacent memory, which may be the target of control flow logic.
Man in the Middle attacks, where an attacker falsifies messages to your program.
Often, a given service isn't obviously vulnerable to any of these. Running under network service (or another account with reduced permissions) is a 'better safe than sorry' strategy that acknowledges two important facts of software development: programmers are fallible and attackers are inventive.
The LocalSystem account is the Windows equivilant of the *nix root account. It's even more privileged than an administrator account. When you run as LocalSystem, you have full access to every resource on the machine.
As others have written, you should write your code to run with the least possible privileges.
The primary difference between LocalService and NetworkService is that services running as NetworkService have the ability to authenticate to other machines in the domain (as the machine account I believe).
Please note that the LocalService and NetworkService accounts both have the "Impersonate" privilege which is a potentially dangerous privilege - it allows the service to impersonate the user who is calling into the service. If that user is an administrator, then even though your code is running in a low privileged service, it can do anything that the administrator does. If an attacker can exploit a buffer overflow in your least privilege service, they can hook out the APIs you use to impersonate your caller and wait until a high privileged caller calls into your service. This technique is known as "Token Kidnapping" and the MSRC has a great blog post describing the issue (and contains links that describe how to mitigate many of the other risks associated with using LocalService and NetworkService accounts).
The Local account has effectively full administrative priviledges on the local machine. Hence any code that might escape from say a buffer overrun and get itself executing has significant scope to do damage.
On the other hand, the Network Service account has by default only Guest level access to the local system. Hence even if an attacker managed to find way to send and execute code within the service that code would have limited access.
If your service has a bug, which can allow attacker to execute arbitrary code (like buffer overflow), he can do everything with your computer if service is running under Local System account, which is equivalent to Administrator account. So the lesser priveleged account your service is running, the lesser privilege the attacker can get.
The simplest scenario is when the service allows the user of the service to execute some code on command line. For example MS SQL Server has a stored procedure that allows you to run a 'command line' command (i.e. run a program).
Let me state first: I know that any user that wants to run a program (or even log in), has to have access to (probably at least) the Windows system directories and the shared libraries in %ProgramFiles%, but I'd like to be able to access Skype, for example, by running it with an unprivileged user and make sure that it can't access any unnecessary files.
I fear that the only way to do this would be to identify all of the gazillion directories where I store files that I don't want this user to access and then create a new user group that can access these directories, or run Skype and Azureus in a VM.
Is there a better way?
Normally, accounts are members of the Users group at least, which does have access to many things. You could make the account a member of no groups, or the Guests group which is very restrictive.
The real issue is that the program's token (an internal security object that keeps track of what security identities a running process has) will contain the Everyone and Authenticated Users groups, which also have read access to lots of stuff. There is no way to create an account without those groups. You could remove the access that Everyone and Authenticated Users groups have to most everything, but it would be a lot of work to track all those down.
I would say that creating a standard user or guest access account for untrusted programs would be plenty secure enough. To support self-updates and to keep related files in the same place, I suggest you install those programs directly in the profile of the user account they will be running as, e.g. C:\Documents and Settings\skype\Program Files\Skype
If you want to get really fancy, you can use a restricted token to either make the Everyone, Authenticated Users, etc. groups deny only (so they can't grant any access) or create a Restricted SID list. This will be difficult to implement because there are global objects that programs will expect to access that the Everyone group has access to, which is normally a safe choice.
See CreateRestrictedToken Function.
There is also an open-source command line program I created a program for creating restricted tokens and job objects on the fly for that purpose: UlimitNT
Maybe sudown is a solution. It's a sudo-similar (as known from Linux) approach to running as unprivileged user, but having the possibility to promote to an administrative account (with password) when needed.
I suppose you could lock down the machine so the user can solely log on, not even start skype with his rights, but start skype by "run as" with sudown.
Besides using a VM you could look into using a Sandbox. Look at Sandboxie fox an example.
simply use acl apis (samples in msdn)