subsystem myipc 500; // Arbitrary name and iduserprefix USERPREF; // Prefix for created functions in the clientserverprefix SERVERPREF; // Prefix for created functions in the server#include<mach/mach_types.defs>#include<mach/std_types.defs>simpleroutineSubtract(server_port : mach_port_t;n1 : uint32_t;n2 : uint32_t);
/* Description of this subsystem, for use in direct RPC */conststruct SERVERPREFmyipc_subsystem SERVERPREFmyipc_subsystem = {myipc_server_routine,500, // start ID501, // end ID(mach_msg_size_t)sizeof(union __ReplyUnion__SERVERPREFmyipc_subsystem),(vm_address_t)0,{{ (mig_impl_routine_t) 0,// Function to call(mig_stub_routine_t) _XSubtract,3,0, (routine_arg_descriptor_t)0, (mach_msg_size_t)sizeof(__Reply__Subtract_t)},}};
macOS IPC: Inter-Process Communication
Inter-Process Communication (IPC) is a set of methods for the exchange of data among multiple threads in one or more processes. macOS provides several IPC mechanisms, including Mach ports, sockets, and Distributed Objects. One of the IPC mechanisms used in macOS is the Mach Interface Generator (MIG), which simplifies the creation of client-server communication interfaces. By understanding how MIG works, an attacker can abuse IPC to escalate privileges on a macOS system.
macOS MIG: Mach Interface Generator
The Mach Interface Generator (MIG) is a tool provided by macOS for automatically generating client-server communication code. MIG simplifies the development of client-server applications by handling the serialization and deserialization of messages sent between processes. This automation can introduce security risks if not properly implemented, allowing attackers to manipulate IPC messages to execute arbitrary code or escalate privileges.
To protect against IPC abuse, developers should carefully design and implement IPC mechanisms, validate message contents, and enforce proper access controls. Additionally, regular security assessments and code reviews can help identify and mitigate potential IPC vulnerabilities in macOS applications.
/* Description of this subsystem, for use in direct RPC */externconststruct SERVERPREFmyipc_subsystem {mig_server_routine_t server; /* Server routine */mach_msg_id_t start; /* Min routine number */mach_msg_id_t end; /* Max routine number + 1 */unsignedint maxsize; /* Max msg size */vm_address_t reserved; /* Reserved */struct routine_descriptor /* Array of routine descriptors */routine[1];} SERVERPREFmyipc_subsystem;
// gcc myipc_server.c myipcServer.c -o myipc_server#include<stdio.h>#include<mach/mach.h>#include<servers/bootstrap.h>#include"myipcServer.h"kern_return_tSERVERPREFSubtract(mach_port_t server_port,uint32_t n1,uint32_t n2){printf("Received: %d - %d = %d\n", n1, n2, n1 - n2);return KERN_SUCCESS;}intmain() {mach_port_t port;kern_return_t kr;// Register the mach servicekr =bootstrap_check_in(bootstrap_port,"xyz.hacktricks.mig",&port);if (kr != KERN_SUCCESS) {printf("bootstrap_check_in() failed with code 0x%x\n", kr);return1;}// myipc_server is the function that handles incoming messages (check previous exlpanation)mach_msg_server(myipc_server,sizeof(union __RequestUnion__SERVERPREFmyipc_subsystem), port, MACH_MSG_TIMEOUT_NONE);}
macOS IPC: Inter-Process Communication
macOS MIG: Mach Interface Generator
Mach Interface Generator (MIG) is a tool used to define inter-process communication (IPC) interfaces for Mach-based systems. It generates client-side and server-side code for message-based IPC. MIG is commonly used in macOS for defining communication interfaces between user-space applications and system services.
To use MIG, you need to define an interface definition file (.defs) that specifies the messages and data structures exchanged between processes. This file is then processed by MIG to generate the necessary C code for handling IPC messages.
By understanding how MIG works and how to define communication interfaces using MIG, you can better understand and manipulate IPC mechanisms in macOS for various purposes, including privilege escalation and security research.
Example:
#include<mach/mach.h>#include<stdio.h>#include"myipc.h"intmain() {mach_port_t server_port;kern_return_t kr; kr =bootstrap_look_up(bootstrap_port,"com.example.myipc",&server_port);if (kr != KERN_SUCCESS) {printf("Failed to look up server port\n");return1; }myipc_do_something(server_port);return0;}
In this example, the client application looks up the server port using bootstrap_look_up() and then calls the myipc_do_something() function to perform some IPC operation with the server.
// gcc myipc_client.c myipcUser.c -o myipc_client#include<stdio.h>#include<stdlib.h>#include<unistd.h>#include<mach/mach.h>#include<servers/bootstrap.h>#include"myipcUser.h"intmain() {// Lookup the receiver port using the bootstrap server.mach_port_t port;kern_return_t kr =bootstrap_look_up(bootstrap_port,"xyz.hacktricks.mig",&port);if (kr != KERN_SUCCESS) {printf("bootstrap_look_up() failed with code 0x%x\n", kr);return1;}printf("Port right name %d\n", port);USERPREFSubtract(port,40,2);}
