Microsoft HEIF Image Extensions (msheif_store.dll): Source-buffer under-allocation in CopyPixels path leads to out-of-bounds read and Access Violation (DoS)

When decoding a crafted HEIF image through WIC, the msheif codec allocates a 1-byte source buffer but later attempts to copy a very large amount of pixel data from that buffer during CopyPixels. The copy uses memmove with a size derived from stride × ROI height, without validating the source buffer’s actual length. This causes an out-of-bounds read and an immediate Access Violation (crash). In practice, opening or previewing the malicious HEIF causes a denial of service in any WIC consumer that routes through the HEIF Image Extensions.

Naming note: Variable names like roi_height are inferred from disassembly for readability and do not reflect vendor symbol names.

Product	Microsoft HEIF Image Extensions
Module	msheif_store.dll
OS	Windows 11
Extension version	1.2.22.0 (Microsoft.HEIFImageExtension_1.2.22.0_x64__8wekyb3d8bbwe\x64\msheif_store.dll)

1. Root Cause Analysis

   a. Detailed description of the vulnerability

   • The decoding pipeline computes a large copy length for memmove based on image geometry (e.g., copy_size = stride * abs(roi_height)).
   • The source buffer that should hold the decoded frame/item data is under-allocated to 1 byte, because:
     • CHEIFStreamReader_ReadItemData calls CHEIFItemInfoEntry_GetDataSize to compute the item’s data length.
     • On a specific failure branch, CHEIFItemInfoEntry_GetDataSize returns success but leaves the computed size as 0.
     • CHEIFStreamReader_ReadItemData then calls MFCreateMemoryBuffer(0, &ppBuffer). Per MF behavior, this produces a buffer with a minimum allocation of 1 byte.
   • Downstream, CopyPixels validates destination buffer size but does not validate source buffer length vs. requested copy size before calling memmove.
   • Result: memmove(dst, src, large_size) reads far past the 1-byte src, faulting at the vectorized load.

   This bug is independently exacerbated if the image/ROI width is mis-parsed (e.g., 0x01000100 = 16,777,472), inflating stride and the final copy size. However, the core vulnerability is source-length not checked against the computed copy length.

(7de0.78e4): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
msheif_store!DllCanUnloadNow+0x228b1d:
00007ffd`841bc45d c5fe6f02        vmovdqu ymm0,ymmword ptr [rdx] ds:000002b0`65be6ff0=c0

0:000> !heap -p -a rdx
    address 000002b065be6ff0 found in
    _DPH_HEAP_ROOT @ 2b05bed1000
    in busy allocation (  DPH_HEAP_BLOCK:         UserAddr         UserSize -         VirtAddr         VirtSize)
                             2b062c2f2d8:      2b065be6ff0                1 -      2b065be6000             2000
    ...
    00007ffe75b90563 MFPlat!operator new+0x0000000000000023
    00007ffe75b83d36 MFPlat!MFCreateMemoryBuffer+0x0000000000000056
    00007ffd840157b1 msheif_store!DllCanUnloadNow+0x0000000000081e71
		...

0:000> r r8
r8=0000000001000100

b. Code flow from input

0:000> k
 # Child-SP          RetAddr               Call Site
00 0000005d`6a9aed98 00007ffe`6fdefcc2     msheif_store!DllCanUnloadNow+0x228b21
01 0000005d`6a9aeda0 00007ffe`6fcb3adc     msheif_store!DllCanUnloadNow+0x18c382
02 0000005d`6a9aee00 00007ffe`6fcb4513     msheif_store!DllCanUnloadNow+0x5019c
03 0000005d`6a9aeef0 00007ffe`6fcb96da     msheif_store!DllCanUnloadNow+0x50bd3
04 0000005d`6a9af0a0 00007fff`318551d5     msheif_store!DllCanUnloadNow+0x55d9a
05 0000005d`6a9af1a0 00007fff`318082eb     windowscodecs!CPyramidBase::CopyPixels+0xf5
06 0000005d`6a9af260 00007fff`31857e52     windowscodecs!CFormatConverter::CopyPixels+0x22b
07 0000005d`6a9af3e0 00007ff6`15fb0f5d     windowscodecs!CFormatConverterResolver::CopyPixels+0xc2
08 0000005d`6a9af480 00007ff6`15fb04ab     heif_decoder!HEIF_LoadBitmapFromMemory+0x34d [C:\\\\Users\\\\test\\\\source\\\\repos\\\\heif_decoder\\\\heif_decoder\\\\heif_decoder.cpp @ 256]
09 0000005d`6a9af670 00007ff6`15fb1754     heif_decoder!HEIF_FuzzMemory+0x9b [C:\\\\Users\\\\test\\\\source\\\\repos\\\\heif_decoder\\\\heif_decoder\\\\heif_decoder.cpp @ 357]
0a 0000005d`6a9af830 00007ff6`15fb3039     heif_decoder!wmain+0x394 [C:\\\\Users\\\\test\\\\source\\\\repos\\\\heif_decoder\\\\heif_decoder\\\\heif_decoder.cpp @ 524]
0b 0000005d`6a9afaa0 00007ff6`15fb2ee2     heif_decoder!invoke_main+0x39 [D:\\\\a\\\\_work\\\\1\\\\s\\\\src\\\\vctools\\\\crt\\\\vcstartup\\\\src\\\\startup\\\\exe_common.inl @ 91]
0c 0000005d`6a9afaf0 00007ff6`15fb2d9e     heif_decoder!__scrt_common_main_seh+0x132 [D:\\\\a\\\\_work\\\\1\\\\s\\\\src\\\\vctools\\\\crt\\\\vcstartup\\\\src\\\\startup\\\\exe_common.inl @ 288]
0d 0000005d`6a9afb60 00007ff6`15fb30ce     heif_decoder!__scrt_common_main+0xe [D:\\\\a\\\\_work\\\\1\\\\s\\\\src\\\\vctools\\\\crt\\\\vcstartup\\\\src\\\\startup\\\\exe_common.inl @ 331]
0e 0000005d`6a9afb90 00007fff`3847e8d7     heif_decoder!wmainCRTStartup+0xe [D:\\\\a\\\\_work\\\\1\\\\s\\\\src\\\\vctools\\\\crt\\\\vcstartup\\\\src\\\\startup\\\\exe_wmain.cpp @ 17]
0f 0000005d`6a9afbc0 00007fff`3939c34c     KERNEL32!BaseThreadInitThunk+0x17
10 0000005d`6a9afbf0 00000000`00000000     ntdll!RtlUserThreadStart+0x2c

Resolved internal calls (renamed for clarity):

CWICHeifDecoderFrame::CopyPixels
 → CWICHeifBitmapSourceBase::CopyPixels_Transform
   → CWICHeifBitmapSourceBase::CopyPixels_Base
     → sub_7FFD8411FC40  // issues memmove
       → memmove         // AV (vmovdqu load from src)

c. Buffer size

• Crafted HEIF that causes CHEIFItemInfoEntry_GetDataSize to take an early “success with size 0” path (e.g., when sub_7FFD8408B898 fails and the function returns success with sizeBuffer = 0).

• Source buffer: Allocated via MFCreateMemoryBuffer(0) ⇒ 1 byte.

• Copy size: Derived as copy_size = stride * abs(roi_height). With mis-parsed width (e.g., 0x01000100) and typical BPP, stride is enormous, leading to a very large copy_size.

• Vulnerable call:

  __int64 sub_7FFD8411FC40(__m128i* dst, __int64 a2, __m128i* src, int a4,
                           unsigned int stride, unsigned int abs_roi_height)
  {
    if (src && dst) {
      if (stride == a2 && stride == a4) {
        // No validation that 'src' contains at least (stride * abs_roi_height) bytes
        memmove(dst, src, (size_t)abs_roi_height * stride); // AV here
      }
    }
  }
  

• Why the source is 1 byte (allocation path):

  __int64 __fastcall CHEIFStreamReader_ReadItemData(__int64 *a1, __int64 *a2, IMFMediaBuffer **a3)
  {
    ppBuffer = 0i64;
    if ( v7(a2) )
    {
      *cbMaxLength = 0i64;
      result = (*(*a2 + 0xA0))(a2, cbMaxLength); // CHEIFItemInfoEntry_GetDataSize
      if ( result < 0 )
      {
        goto LABEL_10;
      }
      if ( *cbMaxLength > 0xC800000ui64 )
      {
        result = 0xC00D36BE;
        goto LABEL_23;
      }
      // cbMaxLength may still be 0 if GetDataSize returned success early
      result = MFCreateMemoryBuffer(cbMaxLength[0], &ppBuffer);
      if ( result < 0 )
      {
        goto LABEL_34;
      }
      ...
  }