[BRLY-LOGOFAIL-2023-018] Memory Corruption vulnerability in DXE driver

Summary

Binarly REsearch Team has discovered an integer overflow on memory allocation size that leads to OOB Write operations during PNG file processing in AMI firmware.

Vulnerability Information

 
• BINARLY internal vulnerability identifier: BRLY-LOGOFAIL-2023-018  
• AMI PSIRT assigned CVE identifier: CVE-2023-39538  
• CVSS v3.1: 8.2 High AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Affected modules with confirmed impact by Binarly team

Potential impact

An attacker with local access can exploit this vulnerability to elevate privileges from ring 3 or ring 0 (depending on the operating system) to a DXE driver and execute arbitrary code. Malicious code installed as a result of this exploitation could survive operating system (OS) boot process and runtime, or modify NVRAM area on the SPI flash storage (to gain persistence). Additionally, threat actors could use this vulnerability to bypass OS security mechanisms (modify privileged memory or runtime variables), influence OS boot process, and in some cases allow an attacker to hook or modify EFI Runtime services.

Vulnerability description

The pseudocode of the vulnerable function is shown below:

unsigned __int64 sub_59844()
{
  unsigned int length; // ebx
  bool v1; // zf
  int width; // ecx
  int heigth; // eax
  void *ZeroPool; // rax
  unsigned __int64 result; // rax
  void *OutputBufferVar; // rax
  __int64 v7; // rcx

  length = 0;
  if ( ColorType )
  {
    switch ( ColorType )
    {
      case 2:
        v1 = ((BitDepth - 8) & 0xFFFFFFF7) == 0;
        break;
      case 3:
        v1 = ((BitDepth - 4) & 0xFFFFFFFB) == 0;
        break;
      case 4:
      case 6:
        v1 = BitDepth == 8;
        break;
      default:
        return 0x8000000000000003ui64;
    }
    if ( v1 )
      goto LABEL_8;
    return 0x8000000000000003ui64;
  }
  if ( BitDepth != 1 && BitDepth != 8 )
    return 0x8000000000000003ui64;
LABEL_8:
  width = PngWidth;
  heigth = PngHeight;
  dword_9733C = PngWidth;
  dword_97340 = PngHeight;
  if ( dword_97350 == 1 && qword_97348 )
  {
    sub_4654(&qword_97348);
    heigth = dword_97340;
    width = dword_9733C;
    qword_97348 = 0i64;
  }
  // BRLY-LOGOFAIL-2023-018: Integer overflow on the allocation size
  ZeroPool = AllocateZeroPool(4 * width * heigth);
  dword_97358 = -1;
  qword_97348 = (__int64)ZeroPool;
  dword_9735C = 0;
  dword_97354 = 0;
  qword_97364 = 0i64;
  dword_97360 = 1;
  dword_9737C = 0;
  dword_97380 = 1;
  if ( OutputBuffer )
    sub_4654(&OutputBuffer);
  switch ( ColorType )
  {
    case 0:
      if ( BitDepth != 1 )
      {
        if ( BitDepth != 2 )
        {
          if ( BitDepth != 4 )
          {
            if ( BitDepth != 8 )
            {
              if ( BitDepth != 16 )
                goto LABEL_47;
              goto LABEL_43;
            }
LABEL_33:
            length = PngWidth;
            goto LABEL_47;
          }
LABEL_44:
          length = (unsigned int)(PngWidth + 1) >> 1;
          goto LABEL_47;
        }
LABEL_45:
        length = (unsigned int)(PngWidth + 3) >> 2;
        goto LABEL_47;
      }
LABEL_46:
      length = (unsigned int)(PngWidth + 7) >> 3;
      goto LABEL_47;
    case 2:
      if ( BitDepth == 8 )
      {
        length = 3 * PngWidth;
      }
      else if ( BitDepth == 16 )
      {
        length = 6 * PngWidth;
      }
      goto LABEL_47;
    case 3:
      if ( BitDepth != 1 )
      {
        if ( BitDepth != 2 )
        {
          if ( BitDepth != 4 )
          {
            if ( BitDepth != 8 )
              goto LABEL_47;
            goto LABEL_33;
          }
          goto LABEL_44;
        }
        goto LABEL_45;
      }
      goto LABEL_46;
  }
  if ( ColorType != 4 )
  {
    if ( ColorType == 6 )
    {
      if ( BitDepth != 8 )
      {
        if ( BitDepth == 16 )
          length = 8 * PngWidth;
        goto LABEL_47;
      }
      goto LABEL_28;
    }
    goto LABEL_47;
  }
  if ( BitDepth == 8 )
  {
LABEL_43:
    length = 2 * PngWidth;
    goto LABEL_47;
  }
  if ( BitDepth == 16 )
LABEL_28:
    length = 4 * PngWidth;
LABEL_47:
  OutputBufferVar = AllocateZeroPool(2 * length);
  v7 = (__int64)OutputBufferVar + length;
  OutputBuffer = (__int64)OutputBufferVar;
  qword_97390 = (__int64)OutputBufferVar;
  result = 0i64;
  qword_97398 = v7;
  return result;
}

As we can see from the pseudocode, the width and height variables are not validated. The attacker can arbitrarly set these variables and thus trigger an integer overflow when ZeroPool is initialized from EfiLibAllocateZeroPool((4 * width * height)). Since ZeroPool is used during the processing of the PNG image, the integer overflow forces the allocation of buffer that is too small to contain the intended data, thus creating an arbitrary heap overflow.

Disclosure timeline

This bug is subject to a 90 day disclosure deadline. After 90 days elapsed or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public.

Acknowledgements

Binarly REsearch Team