I got error CA2122 DoNotIndirectlyExposeMethodsWithLinkDemands on this function :
internal static string GetProcessID()
{
return Process.GetCurrentProcess().Id.ToString(CultureInfo.CurrentCulture);
}
How to fix it?
I got error CA2122
It is not an error, just a warning. The code analysis tool you are using checks for lots of obscure corner-cases, the kind that the C# compiler does not complain about but might be a bad practice. And the kind that programmers are often unaware of. It was originally designed as an internal tool used by Microsoft programmers working on framework code. The rules they must follow are pretty draconian since they can't predict how their code is going to be used.
...WithLinkDemands
A link demand is Code Access Security (CAS) detail. It ensures that code has sufficient rights to execute. Link demands are very cheap, they are checked only once, happens when the code is just-in-time compiled. The "only-once" clause is what the warning is talking about, it is technically possible for code that has sufficient rights to execute first, thus allowing the method to be jitted, but used later by non-trusted code, thus bypassing the check. The tool just assumes that this might happen because the method is public, it doesn't know for a fact that this actually happens in your program.
return Process.GetCurrentProcess()...
It is the Process class that has the link demand. You can tell from the MSDN article which demands it makes. It verifies that the calling code runs in full trust, that it doesn't run in a restrictive unmanaged host like SQL Server and that a derived class meets these demands as well. The Process class is a bit risky, untrusted code could do naughty things by starting a process to bypass CAS checks or to learn too much about the process it runs in and tinker with its configuration.
How to fix it?
More than one possible approach. Roughly in order:
Always high odds that this warning just doesn't apply to your program. In other words, there is no risk of it ever executing code that you don't trust. Your program would have to support plug-ins, written by programmers you don't know about but still have access to the machine to tell your program to load their plug-in. Not very common. Proper approach then is to configure the tool to match your program's behavior, you'd disable the rule.
Evaluate the risk of untrusted code using this method. That ought to be a low one for this specific method, exposing the process ID does not give away any major secrets. It is just a number, it doesn't get to be a risky number until it is used by code that uses Process.GetProcessById(). So you'd consider to suppress the warning, apply the [SuppressMessage] attribute to the method. This is a common outcome, the framework source code has lots and lots of them.
Follow the tool's advice and apply the CAS attributes to this method as well. Simply a copy-paste from the link demands you saw in the MSDN article. This closes the "only-once" loophole, the untrusted code will now fail to jit and can't execute.
Related
I just recently found out here that it is possible (at least in c#) to look up private fields and properties due to reflection.
I was surprised, although I knew that somehow constructs like the DataContractSerializer class need the possibility to access them.
The question now is, if anyone can access every field in my classes, this is kind of insecure, isn't it? I mean what if someone has a private bool _isLicensed field. It could be changed easily!
Later I found out here that the field accessors are not meant as a security mechanism.
So how do I make my Application safe, meaning how do I prevent anyone other than me from changing essential status values inside my classes?
The question now is, if anyone can access every field in my classes, this is kind of insecure, isn't it?
Not everyone can. Only code with sufficient permissions - trusted code. Untrusted code is restricted quite a bit. On the other hand, if the person who wants to use reflection has your assembly, they can run trusted code on their own machine. That's not a new attack vector though, as if they've got your code they could also modify it to make the field public in the first place.
Basically, if code is running on their machine, you should expect them to be able to do pretty much anything with it. Don't rely on access modifiers to keep anything secret.
So how do I make my Application safe, meaning how do I prevent anyone other than me from changing essential status values inside my classes?
If the hostile user is running your code themselves, you pretty much can't. You can make it harder for them, but that's an arms race which is no fun.
So one option in some cases is not to let anyone else run your code - host it on the web in an environment you've locked down. That's not appropriate in all cases, of course.
If you have to let users run the code themselves, you need to weigh up the downsides of them tampering with the costs of making that tampering difficult. We can't really help you with that balancing act - we don't have any idea what your application is, or what the costs involved are (reputational, financial etc).
private public and so on are a part of http://en.wikipedia.org/wiki/Encapsulation. the use is to make your API clear and to avoid mistakes.
there is no solid way to avoid people messing with your program.
you may have noticed that all programs are cracked in a few days usually.
in .net it is VERY easy because of IL code been very readable http://ilspy.net/ and such allow you to take any DLL and just read it like C# code.
you can make it more annoying to read your code using obfuscator
http://en.wikipedia.org/wiki/List_of_obfuscators_for_.NET
but applications like http://de4dot.com/
break this VERY easily.
SecureString is a nice trick: https://msdn.microsoft.com/en-us/library/system.security.securestring%28v=vs.110%29.aspx
writing your code in low level language like c++ might make cracking your code really annoying. but soon a skilled hacker will do whatever he wants with your program.
the only option that might be safe is providing your application as a cloud service where the user only sees the screen output and sends keyboard/mouse input.
This was meant to be a comment for John Skeets answer but ran out of room..
Great answer by the way, but I also must add that code is not meant to be secure its meant to clearly defined.
Most developers know how to change classes and inject into classes. There are many utilities to not only decompile your code but to also allow injection into it.
I wouldn't spend to much effort trying to your make code more secure, I would try and expect the code to be changed. Many programming languages do not have such modifiers as private, public, internal, protected etc. They rely on the developers to understand the consequences of using this code on their own. These programming languages have been quite successful as the developers understand that modifying, calling or injecting into code the API does not specify has results that the developing company cant and will not support.
Therefore, expect your code to be modified and ensure your applications responds to invalid changes appropriately.
Sorry if this seems like a comment...
To add to all the other answers, a simple way of looking at it is this: If the user really wants to break your code, let them. You don't have to support that usage.
Just don't use access modifiers for security. Everything else is user experience.
I want to avoid my program being simple to have the license-verifier part removed from.
I don't want to use a commercial obfuscator because:
Of the cost. And though they can do a better job than I – they
too don't make it impossible to crack, just harder.
It seems that sometimes obfuscators cause bugs in the generated
code.
Obviously, I will be keeping an un-obfuscated copy for maintenance.
I once had to hide a license verifier in code that the customer could modify. Conceivably, they could have removed it if they knew where to look. Here are some tricks that I used at the time.
Give your verifier classes, assembly names, and variable names that look like they actually do something else.
Call the verifier from multiple parts of the code.
Add a randomizer to the call for verification so that sometimes it runs, and sometimes it doesn't. This will make it harder to know where the verification code is actually coming from.
I should add that all of this is defeatable and could cause serious maintenance headaches, but in my particular scenario it worked.
If your intent is to make it harder, but not impossible, one way is to have multiple code points that check your licence file is valid.
Lets say you have a licence file with some key like so
abc-def-fhi-asdf
So, four parts to the key. We would then create four different methods that check for the various parts of the key.
By doing this, and varying the methods used through the code (ideally, randomly choosing the verification method at runtime), you make it significantly more difficult to remove the validation.
on top of this, one method would be to have a publish process that inlined your verification method, subtly changing it each time it is called.
for example something like this:
*user clicks a common function
// [VALIDATION STUB]
*perform user action
The new publish process runs through the code, pulling out // [VALIDATION STUB] and replacing it with your validation code (before the code is compiled), which as I say should vary as much as possible each time.
The main thing to pull from my answer really is that obfuscation is hard, but not impossible. Especially if you resign yourself to the reality that the malevolent user will always break it eventually
I have some suggestions that you may find usefull.
First of course you can use free obfuscators like the one that comes with VisualStudio. It's better than nothing.
Second you can write your license verification code and once it's working fine, refactor it as much as you can, change class names, member variables, local variables and methods to something like c1, v1, l1, m1 and so on. That's basically what obfuscators do.
Third, do all of the above.
Fourth, write your licence verification in unmanaged code (C++, Delphi) and make it a DLL named something important like core.dll, net.dll etc. You can also put some decoy methods in there that would do nothing important. Make many calls to that DLL from multiple places of your code and pretend that you do something with the results of those calls.
Does reflection break the idea of private methods? Because private methods can be accessed from outside of the class? (Maybe I don't understand the meaning of reflection or miss something else, please tell me)
http://en.wikipedia.org/wiki/Reflection_%28computer_science%29
Edit:
If relection breaks the idea of private methods - do we use private methods only for program logic and not for program security?
Thanks
do we use private methods only for program logic and not for program security?
It is not clear what you mean by "program security". Security cannot be discussed in a vacuum; what resources are you thinking of protecting against what threats?
The CLR code access security system is intended to protect resources of user data from the threat of hostile partially trusted code running on the user's machine.
The relationship between reflection, access control and security in the CLR is therefore complicated. Briefly and not entirely accurately, the rules are these:
full trust means full trust. Fully trusted code can access every single bit of memory in the process. That includes private fields.
The ability to reflect on privates in partial trust is controlled by a permission; if it is not granted then partial trust code may not do reflection on privates.
See Link for details.
The desktop CLR supports a mode called "restricted skip visibility" in which the rules for how reflection and the security system interact are slightly different. Basically,
partially trusted code that has the right to use private reflection may access a private field via reflection if the partially trusted code is accessing a private field from a type that comes from an assembly with equal or less trust.
See
Link
for details
The executive summary is: you can lock partially trusted code down sufficiently that it is not able to use reflection to look at private stuff. You cannot lock down full trust code; that's why it's called "full trust". If you want to restrict it then don't trust it.
So: does making a field private protect it from the threat of low trust code attempting to read it, and thereby steal user's data? Yes. Does it protect it from the threat of high trust code reading it? No. If the code is both trusted by the user and hostile to the user then the user has a big problem. They should not have trusted that code.
Note that for example, making a field private does not protect a secret in your code from a user who has your code and is hostile to you. The security system protects good users from evil code. It doesn't protect good code from evil users. If you want to make something private to keep it from a user then you are on a fool's errand. If you want to make it private to keep a secret from evil hackers who have lured the user into running hostile low-trust code then that is a good technique.
Reflection does provide a way to circumvent Java's Access Protection Modifiers and therefore violates strict encapsulation as it realised in C++ and Java. However this does not matter as much as you might think.
Access Protection Modifiers are intended to assist programmers to develop modular well factored systems, not to be uncompromising gate keepers. There are sometimes very good reasons to break strict encapsulation such as Unit Testing and framework development.
While it may initially be difficult to stomach the idea that Access Protection Modifiers are easily circumventable, try to remember that there are many languages (Python, Ruby etc.) that do not have them at all. These languages are used to build large and complex systems just like languages which do provide access protection.
There is some debate on whether Access Protection Modifiers are a help or a hindrance. Even if you do value access protection treat it like a helping hand, not the making or breaking of your project.
Yes, but it is not a problem.
Encapsulation is not about security or secrets, just about organizing things.
Reflection is not part of 'normal' programming. If you want to use it to break encapsulation, you accept the risks (versioning problems etc)
Reflection should only be used when there are no better (less invasive) ways to accomplish something.
Reflection is for system-level 'tooling' like persistence mapping and should be tucked away in well tested libraries. I would find any use of reflection in normal application code suspect.
I started with "it is not a problem". I meant: as long as you use reflection as intended. And careful.
It's like your house. Locks only keep out honest people, or people who aren't willing to pick your lock.
Data is data, if someone is determined enough, they can do anything with your code. Literally anything.
So yes, reflection will allow people to do things you don't want them to do with your code, for example access private fields and methods. However, the important thing is that people will not accidentally do this. If they're using reflection, they know they're doing something they probably aren't intended to do, just like no one accidentally picks the lock on your front door.
No, reflection doesn't break the idea of private methods. At least not per se. There is nothing that says that reflection can't obey access restrictions.
Badly designed reflection breaks the idea of private methods, but that doesn't have anything to do with reflection per se: anything which is badly designed can break the idea of private methods. In particular, a bad design of private methods can also obviously break the idea of private methods.
What do I mean by badly designed? Well, as I said above, there is nothing stopping you from having a language in which reflection obeys access restrictions. The problem with this is that e.g. debuggers, profilers, coverage tools, IntelliSense, IDEs, tools in general need to be able to violate access restrictions. Since there is no way to present different different versions of reflection to different clients, most languages opt for tools over safety. (E is the counterexample, which has absolutely no reflective capabilities whatsoever, as a conscious design choice.)
But, who says that you cannot present different versions of reflection to different clients? Well, the problem is simply that in the classical implementation of reflection, all objects are reponsible for reflecting on themselves, and since there is only one of every object, there can be only version of reflection.
So, where does the idea of bad design come in? Well, note the word "responsible" in the above paragraph. Every object is responsible for reflecting on itself. Also, every object is responsible for whatever it is that it was written for in the first place. In other words: every object has at least two responsibilities. This violates one of the basic principles of object-oriented design: the Single Responsibility Principle.
The solution is rather simple: break up the object. The original object is simply responsible for whatever it was originally written for. And there is another object (called a Mirror because it is an object that reflects other objects) which is responsible for reflection. And now that the responsibility for reflection is broken out into a separate object, what's stopping us from having not one, but two, three, many Mirror Objects? One that respects access restrictions, one that only allows an object to reflect upon itself but not any other objects, one that only allows introspection (i.e. is read-only), one that only allows to reflect on read-only callsite information (i.e. for a profiler), one that gives full access to the entire system including violating access restrictions (for a debugger), one that only gives read-only access to the method names and signatures and respects access restrictions (for IntelliSense) and so on …
As a nice bonus, this means that Mirrors are essentially Capabilities (in the capability-security sense of the word) for reflection. IOW: Mirrors are the Holy Grail on the decade-long quest to reconcile security and runtime dynamic metaprogramming.
The concept of Mirrors was originally invented in Self from where it carried over into Animorphic Smalltalk/Strongtalk and then Newspeak. Interestingly, the Java Debugging Interface is based on Mirrors, so the designers of Java (or rather the JVM) clearly knew about them, but Java's reflection is broken.
Yes, reflection breaks this idea. Native languages also have some tricks to break OOP rules, for example, in C++ it is possible to change private class members using pointer tricks. However, by using these tricks, we get the code which can be incompatible with future class versions - this is the price we pay for breaking OOP rules.
It does, as other already stated.
However, I remember that in Java there can be a security manager active, that could prevent you from accessing any private methods, even with reflection, if you don't have the rights to do so. If you run your local JVM, such a manager is usually not active.
Yes, Reflection could be used to violate encapsulation and even cause incorrect behavior. Keep in mind that the assembly needs to be trusted to perform reflection, so there are still some protections in place.
Yes it breaks the encapsulation, if you want it to. However, it can be put to good use - like writing unit tests for private methods, or sometimes - as I have learned from my own experience - getting around bugs in third party APIs :)
Note that encapsulation != security. Encapsulation is an object oriented design concept and is only meant for improving the design. For security, there is SecurityManager in java.
Yes. Reflection breaks encapsulation principle. That's not only to get access to private members but rather expose whole structure of a class.
I think this is a matter of opinion, but if you are using reflection to get around the encapsulation put in place by a developer on a class, then you are defeating the purpose.
So, to answer your question, it breaks the idea of encapsulation (or information hiding), which simply states that private properties/methods are private so they cant be mucked with outside the class.
Reflection makes it possible for any CLR class to examine and manipulate properties and fields of other CLR classes, but not necessarily to do so sensibly. It's possible for a class to obscure the meaning of properties and fields or protect them against tampering by having them depend in non-obvious fashion upon each other, static fields, underlying OS info, etc.
For example, a class could keep in some variable an encrypted version of the OS handle for its main window. Using reflection, another class could see that variable, but without knowing the encryption method it could not identify the window to which it belonged or make the variable refer to another window.
I've seen classes that claim to act as "universal serializers"; they can be very useful if applied to something like a data-storage-container class which is missing a "serializable" attribute but is otherwise entirely straightforward. They will produce gobbledygook if applied to any class whose creator has endeavored to obscure things.
Yes, it does break encapsulation. But there are many good reasons to use it in some situations.
For example:
I use MSCaptcha in some websites, but it renders a < div> around the < img > tag that messes with my HTML. Then i can use a standard < img> tag and use reflection to get the value of the captcha's image id to construct a URL.
The image id is a private Property but using reflection i can get that value.
access control through private/protected/package/public is not primarily meant for security.
it helps good guys to do the right thing, but doesn't prevent bad guys from doing wrong things.
generally we assume others are good guys, and we include their code into our application without though.
if you can't trust the guy of a library you are including, you are screwed.
Apologies for the shortness of the question, however I don't think it needs much elaboration.
Any there any security implications caused by using the CSharpCodeProvider and could it open a server up for attack?
It depends on how you use it. Here is a summary sorted from the safe use to a use that you certainly don't want to allow (when running the code on a server or some environment that you want to control):
If you use CSharpCodeProvider just for generating C# source code, then you only need a permission to save the generated files to some directory or to noting at all (if it is possible to get the code generated into a memory stream)
If you use it for compiling generated C# source, then you need a permission to run csc.exe (which may not be available in some limited environments such as shared hostings).
If you just generate files & compile them, then it probably won't be harmful (although someone could probably abuse your application to generate many, many files and attack the server using some kind of DOS attack.
If you also load & execute the generated code, then it depends on how you generate it. If you assume that there are no bugs in C#/CodeDOM and can guarantee that the generated code is safe, then you should be fine.
If your code contain things such as CodeSnippetExpression that can be provided by the user (in some way) than the user can write and run anything he or she wants on your server, so this would be potentially quite dangerous.
Sort of. On the surface it's not a direct risk, because you're not running code, just compiling it. However, there's nothing that says that the C# compiler doesn't contain some sort of bug that, given the right malicious input, would cause it to bail out and start executing commands directly.
However, if you later execute the compiled code (and presumably you do -- otherwise why would you compile it to begin with?), it will be running the same context as you are. Obviously, that has all kinds of unpleasant security implications, much like using the quasi-analogous eval() feature of other languages.
It depends on the source that you are compiling. If you have enough control over the source, then it might be an acceptable risk. If you are allowing someone outside of your sphere of trust supply code to the compiler, it might be an unacceptable risk.
I'm trying to think of a way that prevents others from using your published dlls. For example let's say you create a cool lightweight WinUI photo processing tool that's separated into several assemblies. One of them is your precious filters.dll assembly that basically does all of the core filtering work. Once you publish your application, how can you prevent others from taking this filters.dll and using it in other projects?
I've already tried to look at the StrongNameIdentityPermissionAttribute which has a good example here but it doesn't seem to work for me, the code just works without throwing any security exceptions..
Any ideas?
Strong names have nothing to do with preventing or inhibiting reverse engineering. They only serve to stop people substituting assemblies with hacked versions - and only if people havent turned off strong name verification. There's nothing to stop people taking your code, ILDASMing or Reflectoring and re-ILASMing as they see fit.
InternalsVisibleTo and friends are on an honour system at the compiler level too, so not much use for what you're looking for (although for some obfuscators, internals get more agressively obfuscated than publics by default - though this can generally be overcome). My main concern here is to point out that jsut because something is 'internal' doesnt bestow on it any magic code protection pixie dust that stops reverse engineering.
Most of this stuff re why these sort of approaches arent a solution for code protection is summarised very well in this article
There are also code protection products on the market that go beyond obfuscation which sound like the tool for the job you describe.
One method that may work for you is to declare the the methods and classes in the filter assembly to be internal and explicitly specify the assemblies that can access it as "friends".
You do this with an assembly declaration (ususally in assemblyinfo) like:
[assembly:InternalsVisibleTo("cs_friend_assemblies_2")]
see Friend Assemblies for more info.
Also make sure you obfuscate the assembly or people can dig into the code with reflector.
Don't bother worrying too much about protecting your .NET code. If you deploy it to someone elses computer, and that person wants to use or read your code, they will.
If your code is valuable enough you need to keep it on a computer you control (such as a web server) and guard against unauthorised access.
Obfuscation will only slow determined people down. Strong naming and signing is not used to protect your code, but instead to ensure that the user can confirm the code originates from who they expect it to come from (ie ensure it hasn't been tampered with).