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291 lines
13 KiB
Markdown
291 lines
13 KiB
Markdown
# macOS Function Hooking
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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## Function Interposing
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Create a **dylib** with an **`__interpose`** section (or a section flagged with **`S_INTERPOSING`**) containing tuples of **function pointers** that refer to the **original** and the **replacement** functions.
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Then, **inject** the dylib with **`DYLD_INSERT_LIBRARIES`** (the interposing needs occur before the main app lodas). Obviously this restriction has the **restrictions** applied to the use of DYLD\_INSERT\_LIBRARIES. 
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### Interpose printf
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{% tabs %}
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{% tab title="interpose.c" %}
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{% code title="interpose.c" %}
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```c
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// gcc -dynamiclib interpose.c -o interpose.dylib
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#include <stdio.h>
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#include <stdarg.h>
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int my_printf(const char *format, ...) {
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//va_list args;
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//va_start(args, format);
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//int ret = vprintf(format, args);
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//va_end(args);
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int ret = printf("[+] Hello from interpose\n");
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return ret;
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}
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__attribute__((used)) static struct { const void *replacement; const void *replacee; } _interpose_printf
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__attribute__ ((section ("__DATA,__interpose"))) = { (const void *)(unsigned long)&my_printf, (const void *)(unsigned long)&printf };
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```
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{% endcode %}
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{% endtab %}
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{% tab title="hello.c" %}
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```c
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//gcc hello.c -o hello
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#include <stdio.h>
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int main() {
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printf("Hello, World!\n");
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return 0;
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}
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```
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{% endtab %}
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{% endtabs %}
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```bash
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DYLD_INSERT_LIBRARIES=./interpose.dylib ./hello
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[+] Hello from interpose
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```
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## Method Swizzling
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In ObjectiveC this is how a method is called: `[myClassInstance nameOfTheMethodFirstParam:param1 secondParam:param2]`
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It's needed the **object**, the **method** and the **params**. And when a method is called a **msg is sent** using the function **`objc_msgSend`**: `int i = ((int (*)(id, SEL, NSString *, NSString *))objc_msgSend)(someObject, @selector(method1p1:p2:), value1, value2);`
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The object is **`someObject`**, the method is **`@selector(method1p1:p2:)`** and the arguments are **value1**, **value2**.
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Following the object structures, it's possible to reach an **array of methods** where the **names** and **pointers** to the method code are **located**.
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{% hint style="danger" %}
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Note that because methods and classes are accessed based on their names, this information is store in the binary, so it's possible to retrieve it with `otool -ov </path/bin>` or [`class-dump </path/bin>`](https://github.com/nygard/class-dump)
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{% endhint %}
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### Accessing the raw methods
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It's possible to access the information of the methods such as name, number of params or address like in the following example:
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```objectivec
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// gcc -framework Foundation test.m -o test
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#import <Foundation/Foundation.h>
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#import <objc/runtime.h>
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#import <objc/message.h>
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int main() {
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// Get class of the variable
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NSString* str = @"This is an example";
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Class strClass = [str class];
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NSLog(@"str's Class name: %s", class_getName(strClass));
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// Get parent class of a class
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Class strSuper = class_getSuperclass(strClass);
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NSLog(@"Superclass name: %@",NSStringFromClass(strSuper));
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// Get information about a method
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SEL sel = @selector(length);
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NSLog(@"Selector name: %@", NSStringFromSelector(sel));
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Method m = class_getInstanceMethod(strClass,sel);
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NSLog(@"Number of arguments: %d", method_getNumberOfArguments(m));
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NSLog(@"Implementation address: 0x%lx", (unsigned long)method_getImplementation(m));
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// Iterate through the class hierarchy
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NSLog(@"Listing methods:");
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Class currentClass = strClass;
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while (currentClass != NULL) {
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unsigned int inheritedMethodCount = 0;
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Method* inheritedMethods = class_copyMethodList(currentClass, &inheritedMethodCount);
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NSLog(@"Number of inherited methods in %s: %u", class_getName(currentClass), inheritedMethodCount);
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for (unsigned int i = 0; i < inheritedMethodCount; i++) {
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Method method = inheritedMethods[i];
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SEL selector = method_getName(method);
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const char* methodName = sel_getName(selector);
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unsigned long address = (unsigned long)method_getImplementation(m);
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NSLog(@"Inherited method name: %s (0x%lx)", methodName, address);
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}
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// Free the memory allocated by class_copyMethodList
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free(inheritedMethods);
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currentClass = class_getSuperclass(currentClass);
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}
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// Other ways to call uppercaseString method
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if([str respondsToSelector:@selector(uppercaseString)]) {
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NSString *uppercaseString = [str performSelector:@selector(uppercaseString)];
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NSLog(@"Uppercase string: %@", uppercaseString);
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}
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// Using objc_msgSend directly
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NSString *uppercaseString2 = ((NSString *(*)(id, SEL))objc_msgSend)(str, @selector(uppercaseString));
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NSLog(@"Uppercase string: %@", uppercaseString2);
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// Calling the address directly
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IMP imp = method_getImplementation(class_getInstanceMethod(strClass, @selector(uppercaseString))); // Get the function address
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NSString *(*callImp)(id,SEL) = (typeof(callImp))imp; // Generates a function capable to method from imp
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NSString *uppercaseString3 = callImp(str,@selector(uppercaseString)); // Call the method
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NSLog(@"Uppercase string: %@", uppercaseString3);
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return 0;
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}
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```
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### Method Swizzling with method\_exchangeImplementations
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The function method\_exchangeImplementations allows to change the address of one function for the other. So when a function is called what is executed is the other one.
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```objectivec
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//gcc -framework Foundation swizzle_str.m -o swizzle_str
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#import <Foundation/Foundation.h>
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#import <objc/runtime.h>
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// Create a new category for NSString with the method to execute
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@interface NSString (SwizzleString)
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- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from;
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@end
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@implementation NSString (SwizzleString)
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- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from {
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NSLog(@"Custom implementation of substringFromIndex:");
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// Call the original method
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return [self swizzledSubstringFromIndex:from];
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}
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@end
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int main(int argc, const char * argv[]) {
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// Perform method swizzling
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Method originalMethod = class_getInstanceMethod([NSString class], @selector(substringFromIndex:));
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Method swizzledMethod = class_getInstanceMethod([NSString class], @selector(swizzledSubstringFromIndex:));
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method_exchangeImplementations(originalMethod, swizzledMethod);
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// We changed the address of one method for the other
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// Now when the method substringFromIndex is called, what is really coode is swizzledSubstringFromIndex
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// And when swizzledSubstringFromIndex is called, substringFromIndex is really colled
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// Example usage
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NSString *myString = @"Hello, World!";
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NSString *subString = [myString substringFromIndex:7];
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NSLog(@"Substring: %@", subString);
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return 0;
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}
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```
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### Method Swizzling with method\_setImplementation
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The previous format is weird because you are changing the implementation of 2 methods one from the other. Using the function **`method_setImplementation`** you can **change** the **implementation** of a **method for the other one**.
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Just remember to **store the address of the implementation of the original one** if you are going to to call it from the new implementation before overwriting it because later it will be much complicated to locate that address.
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```objectivec
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#import <Foundation/Foundation.h>
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#import <objc/runtime.h>
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#import <objc/message.h>
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static IMP original_substringFromIndex = NULL;
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@interface NSString (Swizzlestring)
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- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from;
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@end
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@implementation NSString (Swizzlestring)
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- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from {
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NSLog(@"Custom implementation of substringFromIndex:");
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// Call the original implementation using objc_msgSendSuper
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return ((NSString *(*)(id, SEL, NSUInteger))original_substringFromIndex)(self, _cmd, from);
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}
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@end
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int main(int argc, const char * argv[]) {
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@autoreleasepool {
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// Get the class of the target method
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Class stringClass = [NSString class];
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// Get the swizzled and original methods
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Method originalMethod = class_getInstanceMethod(stringClass, @selector(substringFromIndex:));
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// Get the function pointer to the swizzled method's implementation
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IMP swizzledIMP = method_getImplementation(class_getInstanceMethod(stringClass, @selector(swizzledSubstringFromIndex:)));
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// Swap the implementations
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// It return the now overwritten implementation of the original method to store it
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original_substringFromIndex = method_setImplementation(originalMethod, swizzledIMP);
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// Example usage
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NSString *myString = @"Hello, World!";
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NSString *subString = [myString substringFromIndex:7];
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NSLog(@"Substring: %@", subString);
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// Set the original implementation back
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method_setImplementation(originalMethod, original_substringFromIndex);
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return 0;
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}
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}
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```
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## Hooking Attack Methodology
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In this page different ways to hook functions were discussed. However, they involved **running code inside the process to attack**.
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In order to do that the easiest technique to use is to inject a [Dyld via environment variables or hijacking](../macos-dyld-hijacking-and-dyld\_insert\_libraries.md). However, I guess this could also be done via [Dylib process injection](macos-ipc-inter-process-communication/#dylib-process-injection-via-task-port).
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However, both options are **limited** to **unprotected** binaries/processes. Check each technique to learn more about the limitations.
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However, a function hooking attack is very specific, an attacker will do this to **steal sensitive information from inside a process** (if not you would just do a process injection attack). And this sensitive information might be located in user downloaded Apps such as MacPass.
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So the attacker vector would be to either find a vulnerability or strip the signature of the application, inject the **`DYLD_INSERT_LIBRARIES`** env variable through the Info.plist of the application adding something like:
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```xml
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<key>LSEnvironment</key>
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<dict>
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<key>DYLD_INSERT_LIBRARIES</key>
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<string>/Applications/MacPass.app/Contents/malicious.dylib</string>
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</dict>
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```
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Add in that library the hooking code to exfiltrate the information: Passwords, messages...
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## References
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* [https://nshipster.com/method-swizzling/](https://nshipster.com/method-swizzling/)
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/hacktricks\_live)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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