Code Injection with Dyld Interposing

Swizzling handles Objective-C methods, but cannot be used for C/C++ functions. When reverse engineering iOS apps some non-Obj-C lower level calls might be most useful, and sometimes you need to intercept them in an app that you don’t have the source code for.

While not strictly necessary for interposing, inserted libraries are commonly combined with interposing and are a fantastic resource for anyone exploring iOS internals, so it’s worth a quick overview.

Dyld Binding

Interposing

Looking at the source code for dyld, we can see exactly where these interposed addresses are loaded:

Now putting this all together, we can see how to implement a framework that does what we wanted from our original example:

[1] If you’re interested in other dyld environment variables, check out man dyld

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