# macOS函数挂钩

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## 函数替换

创建一个包含指向**原始函数**和**替换函数**的**函数指针**元组的**dylib**，并带有一个**`__interpose`**部分（或带有**`S_INTERPOSING`**标志的部分）。

然后，使用**`DYLD_INSERT_LIBRARIES`**注入dylib（替换需要在主应用程序加载之前发生）。显然，这个限制受到了对DYLD\_INSERT\_LIBRARIES使用的限制。&#x20;

### 替换printf

{% tabs %}
{% tab title="interpose.c" %}
{% code title="interpose.c" %}
```c
// gcc -dynamiclib interpose.c -o interpose.dylib
#include <stdio.h>
#include <stdarg.h>

int my_printf(const char *format, ...) {
//va_list args;
//va_start(args, format);
//int ret = vprintf(format, args);
//va_end(args);

int ret = printf("[+] Hello from interpose\n");
return ret;
}

__attribute__((used)) static struct { const void *replacement; const void *replacee; } _interpose_printf
__attribute__ ((section ("__DATA,__interpose"))) = { (const void *)(unsigned long)&my_printf, (const void *)(unsigned long)&printf };
```
{% endcode %}
{% endtab %}

{% tab title="hello.c" %}
```c
//gcc hello.c -o hello
#include <stdio.h>

int main() {
printf("Hello, World!\n");
return 0;
}
```
{% endtab %}
{% endtabs %}
```bash
DYLD_INSERT_LIBRARIES=./interpose.dylib ./hello
[+] Hello from interpose
```
## 方法交换

在ObjectiveC中，方法的调用方式是：`[myClassInstance nameOfTheMethodFirstParam:param1 secondParam:param2]`

需要提供**对象**、**方法**和**参数**。当调用方法时，会使用函数**`objc_msgSend`**发送一条消息：`int i = ((int (*)(id, SEL, NSString *, NSString *))objc_msgSend)(someObject, @selector(method1p1:p2:), value1, value2);`

对象是**`someObject`**，方法是**`@selector(method1p1:p2:)`**，参数是**value1**和**value2**。

根据对象的结构，可以找到一个包含方法**名称**和**指向方法代码的指针**的方法数组。

{% hint style="danger" %}
请注意，由于方法和类是根据名称访问的，这些信息存储在二进制文件中，因此可以使用`otool -ov </path/bin>`或[`class-dump </path/bin>`](https://github.com/nygard/class-dump)来检索它们。
{% endhint %}

### 访问原始方法

可以访问方法的信息，例如名称、参数数量或地址，如下面的示例所示：
```objectivec
// gcc -framework Foundation test.m -o test

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>

int main() {
// Get class of the variable
NSString* str = @"This is an example";
Class strClass = [str class];
NSLog(@"str's Class name: %s", class_getName(strClass));

// Get parent class of a class
Class strSuper = class_getSuperclass(strClass);
NSLog(@"Superclass name: %@",NSStringFromClass(strSuper));

// Get information about a method
SEL sel = @selector(length);
NSLog(@"Selector name: %@", NSStringFromSelector(sel));
Method m = class_getInstanceMethod(strClass,sel);
NSLog(@"Number of arguments: %d", method_getNumberOfArguments(m));
NSLog(@"Implementation address: 0x%lx", (unsigned long)method_getImplementation(m));

// Iterate through the class hierarchy
NSLog(@"Listing methods:");
Class currentClass = strClass;
while (currentClass != NULL) {
unsigned int inheritedMethodCount = 0;
Method* inheritedMethods = class_copyMethodList(currentClass, &inheritedMethodCount);

NSLog(@"Number of inherited methods in %s: %u", class_getName(currentClass), inheritedMethodCount);

for (unsigned int i = 0; i < inheritedMethodCount; i++) {
Method method = inheritedMethods[i];
SEL selector = method_getName(method);
const char* methodName = sel_getName(selector);
unsigned long address = (unsigned long)method_getImplementation(m);
NSLog(@"Inherited method name: %s (0x%lx)", methodName, address);
}

// Free the memory allocated by class_copyMethodList
free(inheritedMethods);
currentClass = class_getSuperclass(currentClass);
}

// Other ways to call uppercaseString method
if([str respondsToSelector:@selector(uppercaseString)]) {
NSString *uppercaseString = [str performSelector:@selector(uppercaseString)];
NSLog(@"Uppercase string: %@", uppercaseString);
}

// Using objc_msgSend directly
NSString *uppercaseString2 = ((NSString *(*)(id, SEL))objc_msgSend)(str, @selector(uppercaseString));
NSLog(@"Uppercase string: %@", uppercaseString2);

// Calling the address directly
IMP imp = method_getImplementation(class_getInstanceMethod(strClass, @selector(uppercaseString))); // Get the function address
NSString *(*callImp)(id,SEL) = (typeof(callImp))imp; // Generates a function capable to method from imp
NSString *uppercaseString3 = callImp(str,@selector(uppercaseString)); // Call the method
NSLog(@"Uppercase string: %@", uppercaseString3);

return 0;
}
```
### 使用method\_exchangeImplementations进行方法交换

函数method\_exchangeImplementations允许将一个函数的地址更改为另一个函数的地址。因此，当调用一个函数时，实际执行的是另一个函数。
```objectivec
//gcc -framework Foundation swizzle_str.m -o swizzle_str

#import <Foundation/Foundation.h>
#import <objc/runtime.h>


// Create a new category for NSString with the method to execute
@interface NSString (SwizzleString)

- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from;

@end

@implementation NSString (SwizzleString)

- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from {
NSLog(@"Custom implementation of substringFromIndex:");

// Call the original method
return [self swizzledSubstringFromIndex:from];
}

@end

int main(int argc, const char * argv[]) {
// Perform method swizzling
Method originalMethod = class_getInstanceMethod([NSString class], @selector(substringFromIndex:));
Method swizzledMethod = class_getInstanceMethod([NSString class], @selector(swizzledSubstringFromIndex:));
method_exchangeImplementations(originalMethod, swizzledMethod);

// We changed the address of one method for the other
// Now when the method substringFromIndex is called, what is really coode is swizzledSubstringFromIndex
// And when swizzledSubstringFromIndex is called, substringFromIndex is really colled

// Example usage
NSString *myString = @"Hello, World!";
NSString *subString = [myString substringFromIndex:7];
NSLog(@"Substring: %@", subString);

return 0;
}
```
### 使用method\_setImplementation进行方法交换

之前的格式很奇怪，因为你正在改变一个方法的实现方式，将其替换为另一个方法。使用函数**`method_setImplementation`**，你可以将一个方法的实现方式**更改为另一个方法**。

只需记住，如果你打算在新的实现方式中调用原始方法的实现方式，**请先存储原始方法实现方式的地址**，因为稍后要定位该地址将变得更加复杂。
```objectivec
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>

static IMP original_substringFromIndex = NULL;

@interface NSString (Swizzlestring)

- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from;

@end

@implementation NSString (Swizzlestring)

- (NSString *)swizzledSubstringFromIndex:(NSUInteger)from {
NSLog(@"Custom implementation of substringFromIndex:");

// Call the original implementation using objc_msgSendSuper
return ((NSString *(*)(id, SEL, NSUInteger))original_substringFromIndex)(self, _cmd, from);
}

@end

int main(int argc, const char * argv[]) {
@autoreleasepool {
// Get the class of the target method
Class stringClass = [NSString class];

// Get the swizzled and original methods
Method originalMethod = class_getInstanceMethod(stringClass, @selector(substringFromIndex:));

// Get the function pointer to the swizzled method's implementation
IMP swizzledIMP = method_getImplementation(class_getInstanceMethod(stringClass, @selector(swizzledSubstringFromIndex:)));

// Swap the implementations
// It return the now overwritten implementation of the original method to store it
original_substringFromIndex = method_setImplementation(originalMethod, swizzledIMP);

// Example usage
NSString *myString = @"Hello, World!";
NSString *subString = [myString substringFromIndex:7];
NSLog(@"Substring: %@", subString);

// Set the original implementation back
method_setImplementation(originalMethod, original_substringFromIndex);

return 0;
}
}
```
## 钩子攻击方法论

在本页面中，讨论了不同的函数钩子方式。然而，它们都涉及到在进程内运行代码来进行攻击。

为了做到这一点，最简单的技术是通过环境变量或劫持来注入[Dyld](../macos-dyld-hijacking-and-dyld\_insert\_libraries.md)。然而，我猜这也可以通过[Dylib进程注入](macos-ipc-inter-process-communication/#dylib-process-injection-via-task-port)来实现。

然而，这两种选项都**限制**于**未受保护**的二进制文件/进程。请查看每种技术以了解更多限制信息。

然而，函数钩子攻击非常具体，攻击者会使用这种方法来从进程内部窃取敏感信息（如果不是这样，你只会进行进程注入攻击）。而这些敏感信息可能位于用户下载的应用程序中，如MacPass。

因此，攻击者的方式要么是找到一个漏洞，要么是剥离应用程序的签名，通过应用程序的Info.plist注入**`DYLD_INSERT_LIBRARIES`**环境变量，添加类似以下内容：
```xml
<key>LSEnvironment</key>
<dict>
<key>DYLD_INSERT_LIBRARIES</key>
<string>/Applications/MacPass.app/Contents/malicious.dylib</string>
</dict>
```
在该库中添加挂钩代码以窃取信息：密码、消息...

## 参考资料

* [https://nshipster.com/method-swizzling/](https://nshipster.com/method-swizzling/)

<details>

<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks 云 ☁️</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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* 发现我们的独家[**NFTs**](https://opensea.io/collection/the-peass-family)收藏品——[**The PEASS Family**](https://opensea.io/collection/the-peass-family)
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</details>