CVE-2022-21971: prauthproviders의 초기화되지 않은 포인터 해제

근본 원인

WapAuthProvider::CreateInstance 생성자는 WapAuthProvider 객체(0x78바이트)를 할당하고 초기화하지만 해당 상태를 완전히 초기화하지는 못합니다.

오프셋 0x50의 포인터는 초기화되지 않은 상태이며, 소멸자(WapAuthProvider::~WapAuthProvider)가 호출될 때 해제(free)됩니다:

prauthproviders!WapAuthProvider::~WapAuthProvider+0x38:
00007ffd`a91f3078 488b4b50        mov     rcx,qword ptr [rbx+50h] ds:000001cf`efe35fd0=c0c0c0c0c0c0c0c0

0:011> 
prauthproviders!WapAuthProvider::~WapAuthProvider+0x3c:
00007ffd`a91f307c 4883634000      and     qword ptr [rbx+40h],0 ds:000001cf`efe35fc0=0000000000000000

0:011> 
prauthproviders!WapAuthProvider::~WapAuthProvider+0x41:
00007ffd`a91f3081 48ff1578ad0000  call    qword ptr [prauthproviders!_imp_LocalFree (00007ffd`a91fde00)] ds:00007ffd`a91fde00={KERNELBASE!LocalFree (00007ffd`ccdb0620)

다음은 초기화되지 않은 데이터를 사용하는 함수입니다. [0]과 [1]을 참고하세요:

void WapAuthProvider::~WapAuthProvider(__int64 this) {
  void *v2; // rcx
  void *v3; // rcx

  *(_QWORD *)this = &WapAuthProvider::`vftable';
  LocalFree(*(HLOCAL *)(this + 56));
  v2 = *(void **)(this + 64);
  *(_QWORD *)(this + 56) = 0i64;
  LocalFree(v2);
  v3 = *(void **)(this + 80);       // <-- [0] uninitialized
  *(_QWORD *)(this + 64) = 0i64;
  LocalFree(v3);                    // <-- [1] free
  *(_QWORD *)(this + 80) = 0i64;
}

재현

winword.exe에서 Gflags를 통해 PageHeap을 켭니다.
Word를 시작하고 디버거를 연결합니다.
Word에서 cve-2022-21971.rtf를 엽니다.

(1c84.11b4): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
verifier!AVrfpDphFindBusyMemoryNoCheck+0x8a:
00007ffd`78d84742 817ac0bbbbcdab  cmp     dword ptr [rdx-40h],0ABCDBBBBh ds:c0c0c0c0`c0c0c080=????????

0:011> kc
 # Call Site
00 verifier!AVrfpDphFindBusyMemoryNoCheck
01 verifier!AVrfpDphFindBusyMemory
02 verifier!AVrfpDphFindBusyMemoryAndRemoveFromBusyList
03 verifier!AVrfDebugPageHeapFree
04 ntdll!RtlDebugFreeHeap
05 ntdll!RtlpFreeHeap
06 ntdll!RtlpFreeHeapInternal
07 ntdll!RtlFreeHeap
08 KERNELBASE!LocalFree
09 prauthproviders!WapAuthProvider::~WapAuthProvider
0a prauthproviders!WapAuthProvider::`vector deleting destructor'
0b prauthproviders!WapAuthProvider::Release
0c prauthproviders!CClassFactory::CreateInstance
0d combase!CServerContextActivator::CreateInstance
0e combase!ActivationPropertiesIn::DelegateCreateInstance
0f combase!CApartmentActivator::CreateInstance

Windows 10 x64 VM과 Windows 11 x64에서 Wordpad(단, 클릭 한 번 필요) 및 Office Word 2019로 재현했습니다.

CVE-2022-21971-Windows-Runtime-RCE

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