In C++ applications, runtime type information (RTTI) is a powerful feature that allows programmers to determine the type of an object at runtime. However, exposing RTTI in a production environment can pose security risks and lead to vulnerabilities in the software. In this article, we will discuss techniques for securing and protecting runtime type information in C++ applications.

1. Disable RTTI

By default, C++ enables RTTI which allows dynamic type identification using typeid and dynamic_cast. However, if the application does not require this feature, it is recommended to disable RTTI altogether. Disabling RTTI eliminates the associated data structures and reduces the attack surface.

To disable RTTI in C++, add the following compiler flag when building the application:

-fno-rtti

By disabling RTTI, the application becomes less susceptible to attacks that leverage knowledge of object types.

2. Implement Custom Type Identification Mechanisms

Instead of relying on built-in RTTI mechanisms, consider implementing custom type identification mechanisms. This approach helps prevent the exposure of sensitive type information and provides better control over class hierarchies.

Tagging Mechanism

One commonly used technique is the tagging mechanism, wherein each class is associated with a unique tag. A tagged base class can be used as the parent for all classes that require identification. This way, only the tags are exposed, protecting the actual class structure.

class TaggedBase
{
public:
    virtual int GetTag() const = 0;
};

class MyCustomClass : public TaggedBase
{
public:
    int GetTag() const override
    {
        return 1; // Unique tag for MyCustomClass
    }
};

Covariant Return Types

Another technique is using covariant return types. By returning a different type in derived classes, you can avoid exposing the actual class hierarchy while still providing the necessary functionality.

class Base
{
public:
    virtual Base* Clone() const = 0;
};

class Derived : public Base
{
public:
    Derived* Clone() const override
    {
        return new Derived(*this);
    }
};

Using covariant return types, the specific derived class type can be obtained without exposing the base class implementation.

Conclusion

Securing and protecting runtime type information is crucial in C++ applications to prevent vulnerabilities and potential attacks. By employing techniques such as disabling RTTI and implementing custom type identification mechanisms like the tagging mechanism or covariant return types, developers can enhance the security of their applications.

#C++ #RuntimeTypeInfo #Security