I've written a small service (plain Win32) and I'd like to know if it's possible to run multiple instances of it when multiple users are logged on.
Basically, let's say we've got UserA and UserB for UserA the service would log on as "domain\UserA" and for UserB the service would log on as "domain\UserB" - this is from the same executable of course. I can change the logon dynamically using the ChangeServiceConfig() function, but it changes it system-wide it seems, while I'd like each user to have his own copy of the service running only for him.
Thank you in advance for any pointers.
Win32 services are designed to be system-wide, and start running before any user is logged in. If you want something to run on a per-user basis, it's probably better to design it as a regular application and run it from the user's Startup group.
Is it possible to perhaps have the service create child processes which then adopt the user credentials (or be started with them)? This way you're still limited to a single instance of the service, but it is able to do its per-user jobs all the same. IIRC the Windows Task Scheduler service does this.
The whole concept of a service is that it is started before any user is even logged on. so even if this was possible, you wouldn't be able to choose between userA and userB when the service starts because none of them is logged on yet.
A possible direction would be for the service to run as SYSTEM And every few minutes check if there is a user logged in, if there is- impersonate that user and do this stuff.
Yes, that sounds close (I'm answering comment from Greg, but comments are too short to fit my reply).
I don't know the list of users beforehand, but there's a GUI control application that would be used to enter username/password pairs for each user. So, userA would log on, run the application, enter his credentials and service would use that. At the same time (after userA has logged off, but the service is still running with userA's credentials) userB logs on, uses the app, and another copy of the service starts running as logged on userB. Thus, at the same time userA and userB services are running.
Is that possible?
You are probably looking to Impersonate the users. Check out some references I found with a quick Google search here:
MSDN Article on WindowsIdentity.Impersonate
.Net Security Blog Article
It sounds as if you actually have two different, conflicting requirements, as to timing and identity.
Run as each logged in user
Run automatically even if no user is logged in.
No way to do this trivially, instead consider wrapping your program in a service; the program will run normally on startup for each user (either thru the startup folder or taskscheduler), and in addition create a service to run your app as a system user (or any other user you define).
Since you also need (you mention this in the comments) the app to keep running as the enduser even after he logs out, you can have the service manage this process for you.
HOWEVER this might not be the best idea, since the user is still effectively logged in. This can have numerous side effects, including security, performance (too many users logged in at once...), etc.
You could create an service application and a non-service(normal) application and make them communicate through IPC (Mapped File, Pipes, MailSolts ... you name it).
This way you solve all the troubles.
NOTE: The same application can behave differently - when started as a process and when started by a user, but in the end it is the same thing, you still have 2 applications (no matter if you got only one executable).
Running with different accounts is possible. In fact, this is common. See svchost.exe, which implements a bunch of OS services.
I just don't get how you determine which accounts. In a big company, many PCs are set up so all 100.000+ employees could use it. You don't want to run your service as the logged-in users, nor can you want to run it for all 100.000 users. So for which accounts, I have to ask?
A Windows process can only execute with the privileges of one single user at a time. This applies to services and other processes. With enough privileges it is possible to "switch" between different users by using impersonation. The most common pattern for what you are trying to do is to have one instance of a privileged service which registers to log in/log out events and creates children processes accordingly, each one of them impersonating the logged in user. The pattern will also simplify UI as each process runs on each separate user's Desktop, as if it were a regular application.
If you keep the privileged service's code as simple as possible this pattern has the added benefit that you are minimizing the attack surface of your code. If a user finds a security problem on the "running as user" side of your service it is a non-issue, while security problems in the privileged services could lead to privilege escalation. In fact, before Vista privileged services implementing a Windows message processing loop are vulnerable to a type of attack called Shatter attacks, which you should be aware of given what you are trying to do.
You want this running all the time, so you want a service.
You want something tracking each user, so you want an application which runs in the user session and communicates with the service (using named pipes or DCOM or whatever fits your requirements).
You don't need multiple instances of your service. From the description of your problem it looks like what you need is one service that can impersonate users and execute jobs on their behalf.
You can do this by implementing a COM object hosted in a service. Your client application (that the end user runs) will call CoCreateInstanceEx on your CLSID. This would cause new instance of your COM object to be created in your service. Then the application can use a method on one of your interfaces to pass the collected user credentials to the COM object (though I'd be wary of collecting credentials and instead see if I can pass the user token instead). The COM object which is running in the context of the service can then call LogonUser() to log on the user and impersonate it, so it can do whatever on her behalf (like finding the user local appdata folder :-)). Other answers havve good links to impersonating users using credentials or token.
If you feel comfortable with COM, I'd suggest you create your objects as multithreaded (living in the MTA), so that their execution is not serialized by COM. If not, the default single threaded model would be good enough for you.
The Visual Studio ATL wizard can generate the skeleton of a COM object living in a service. You can also read about implementing Windows Service with ATL here: http://msdn.microsoft.com/en-us/library/74y2334x(VS.80).aspx
If you don't know COM at all, you can use other communication channels to pass the credentials to your service.
In any case, once your service gets the credentials, all the work on behalf of the user will have to be executed on a background thread, so as to not block the application running as the user.
Related
I am writing a C++ application with a postgresql 9.2 database backend. It is an accounting software. It is a muti user application with privilege separation features.
I need help in implementing the user account system. The privileges for users need not be mutually exclusive. Should I implement it at the application level, or at the database level?
The company is not very large at present. Assume about 15-20 offices with an average of 10 program users per office.
Can I make use of the roles in postgres to implement this? Will it become too tedious, unmanageable or are there some flaws in such an approach?
If I go via the application route, how do I store the set of privileges a user has? Will a binary string suffice? What if there are additional privileges later, how can I incorporate them? What do I need to do to ensure that there are no security issues? And in such an approach I am assuming the application connects with the privileges required for the most privileged user.
Some combination of the two methods? Or something entirely different?
All suggestions and arguments are welcome.
Never provide authorization from a client application, which is run on uncontrolled environment. And every device, that a user has physical access to, is an uncontrolled environment. This is security through obscurity — a user can simply use a debugger to get a database access credentials from client program memory and just use psql to do anything.
Use roles.
When I was developing an C++/PostgreSQL desktop application I've chosen to disallow all users access to modify all tables and I've created an API using Pl/PgSQL functions with VOLATILE SECURITY DEFINER options. But I think it wasn't a best approach, as it's not natural and error prone to use for example:
select add_person(?,?,?,?,?,?,?,?,?,?,?,?);
I think a better way would be to allow modifications to tables which a user needs to modify and, when needed, enforce authorization using BEFORE triggers, which would throw an error when current_user does not belong to a proper role.
But remember to use set search_path=... option in all functions that have anything to do with security.
If you want to authorize read-only access to some tables then it gets even more complicated. Either you'd need to disable select privilege for these tables and create API using security definer functions for accessing all data. This would be a monster size API, extremely ugly and extremely fragile. Or you'd need to disable select privilege for these tables and create views for them using create view with (security_barrier). Also not pretty.
I am developing an application that works with PostgreSQL and other database features that require a username and password to login to the remote server to store the data. The user has to be able to set the username and password which would then be stored in a configuration file on disk. The problem is that anybody can open the configuration file and read the credentials creating a serious security problem.
I have done some research on encrypting the whole configuration file and then de-crypting it when needed, but the problem is that a hacker could put the program though a debugger and easily find out the decryption key. What is the best method to keep configuration data secret on Windows using C/C++?
The moment an Attacker is able to attach a debugger to your running program is the moment the game is over. Being able to debug your program means that your user account or the underlying OS is compromised, which means every security measure on your app's behalf is futile. The attacker will (with knowledge, persistence and motivation) know everything you enter into your computer, or have entered and stored before.
The user has to be able to set the username and password which would
then be stored in a configuration file on disk
This is the weak spot and this is what you need to change.
(On a side note, is the password you store never going to change? That's another security weak spot.)
As stated in Eugen Rieck's answer, if the attacker has physical access to your system he will, in time, break all your defenses.
The simple solution is clear: don't let him have access to the system that handles security/authorization. Have the SQL server on a dedicated, remote machine and let it handle the username/password validation.
Or, make your app multi tiered with part on a remote machine that handles the user authentication and routs your DB queries.
This will mean that your user will have to login every time they start your application.
(Preferably also after a pre-set period of inactivity.)
It all depends on how safe you need to be. It's important to understand that security is not easy to create and you should always try to use existing frameworks if possible.
In Windows would it be possible to protect data within a single program? I have been looking into CryptProtectData but whis is by user basis I would like something simular but on program basis. My program will have multiple users that require access to the same data, but the data is sentitive and I dont want any user to read it.
First of all, if your user has administrator privileges, there is no definite way to keep them out.
Second, even if they didn't, you'd have to implement part of your software at ring 0, so it would have a higher privilege than the user, which would make it harder for them to get access to the process' memory or executables. You could then encrypt your data and decrypt it when you serve it to the user.
If all of the above is not possible, you can employ the same obfuscation techniques that software developers use against cracking.
That usually comes down to preventing debugging or preventing patching. Some advice here: http://www.woodmann.com/crackz/Tutorials/Protect.htm
CryptProtectData (indirectly) uses user's credentials to encrypt the data.
On Windows (as well as on most other general-purpose computer platforms) it is not possible to encrypt the data on per-application basis cause the computer belongs to users and the user is the master, not the application.
If you don't want the data to be accessible for the user (and other applications running under user's account), you need to move this data out of the computer, store it on the remote system and control user's access to this data.
If your users do not have administrator privileges then what I would do is have your program create an account for its own purposes. When your program creates its data files, it would set the ACLs on those files so that the account it created is the only one with any access to those files. Whenever your program needed to read/write those files, it would need to temporarily login using its special account. The problem is then to keep the login credentials for that account secret. That's another problem entirely.
I'm interested in what strategies can be used for handling user authentication and authorization in a cross-platform distributed system. I would like to be able to mark actions in the system as belonging to a certain user and also to only allow certain users to do certain actions.
Background:
The system is currently used under Windows only, where actions initiated by a user is currently only tagged as coming from the particular machine of the user. An action basically involves using the cpu for doing some calculations and returning the result.
There is currently no authorization whatsoever being done and no authentication of users (or between computers). The system is running as a service with low privileges (using the NETWORK SERVICE account). Data is not sensitive and all users on the local network are allowed to use the system to their hearts content.
The system can be deployed in both homogeneous Windows domain setups as well as workgroups without a domain controller or with a mix of a domain together with a bunch of worker computers not belonging to the domain.
Problem
In order to add functionality to the system, say for instance collecting usage statistics per user or displaying who is making use of a computer it is necessary to keep track of individual users. In addition to this, if certain actions should only be allowed to be performed by certain users (for instance changing some settings for the system), some form of authorization is also required.
I have a good understanding of the Windows way of doing this and adding this type of functionality in a homogeneous Windows domain setup would be straightforward using the built-in authentication and authorization functionality in Windows. This also eliminates the need to assign special accounts only valid for this particular system to the system - once the user has logged in normally all authentication and authorization can be done without requiring any extra user interaction.
But what if the system should be able to run on Mac OSX? Or Linux? What if it is supposed to run in a mixed environment with some users in a Windows domain, others on OSX and some worker machines running Linux? (The actual system can be ported to all of these systems and handles cross-platform communication and so on). I have limited knowledge of the way authentication and authorization is handled on these platforms and no knowledge of how this can be achieved when interacting between platforms.
Are there any good strategies to use for cross-platform user authentication and authorization in a distributed system like this? Note the dual use of "cross-platform" here - both as in being able to compile the program for different platforms and as in being able to interact between platforms.
I've tagged the question as C++, since this is the language the system is written in, but I am willing to accept anything that can be interacted with using C++. Any ideas (including wild architectural changes) are welcome!
Update:
An example of what would be interesting to be able to achieve:
User A is logged in to machine 1, which is a Windows machine.
User A opens the administrative interface for the system, selects machine 2 (a Linux system) and adjusts a setting. The system verifies that user A in fact has sufficient privileges to be allowed to do this.
Since A already verified his identity when he/she logged in, it would be desirable to allow him/her to change this setting without having to provide additional credentials.
You chould use claims based authentication with SAML tokens, which work cross platform.
On the windows side there is a library for this: Windows Identity Foundation.
See: http://msdn.microsoft.com/en-us/security/aa570351
Nowadays a lot of web applications are providing API for other applications to use.
I am new to the usage of API so I want to understand the use cases for it.
Lets take Basecamp as an example.
What are the use cases for using their API in my web application?
For inserting current data in my web application into a newly created Basecamp account instead of inserting everything manually which could take days or weeks if the data is huge?
For updating my application data when the user changes something in Basecamp. If so, how do I know for example when a user add/edit/remove a contact in Basecamp. Do I make a request and check every minute from the backend?
For making backup of the Basecamp data so I can move it to other applications if necessary?
Are all the above examples good use cases for the usage of API?
Are there more use cases?
I want to have a clear picture of why it's good to use another web service API and how I can leverage that on my application.
Thanks.
I've found the biggest reason to use and provide web services is to be able to programmatically drive the application with another process. This allows the coupling of different actions in different applications driven by one event/process/trigger.
For example I could create a use a webservice provided by Basecamp, my bug tracking database and the continuous integration server. I could tie all those things together and kick them off from a commit hook script.
I can have a monitor in production automatically open a ticket in our ticket tracker. This could trigger an autoremediation process from the ticket tracker which logs into the box remotely and restarts the service.
The other major reason I've seen to use and provide web service is to reduce double entry. If you do change management in your production environment that usually means you create Change tickets. The changes that occur may also need to be reflected in the Change Management Database which is usually a model of how production is suppose to look. Most of these systems don't automatically drive the update of your configuration item with the data from the change. Using web services you can stitch them together to eliminate the double (manual) entry that would normally occur.
APIs are used any time you want to get data to/from an application without using the default interface.
*I'd bet there's a mobile app would use the basecamp api.
*You could use the api to pull information from basecamp into another application (like project manager software or an individual's todo webpage)
*the geekiest of us may prefer to update basecamp from a script/command line rather than interrupting our work flow to open a web page and click around.