[BRLY-LOGOFAIL-2023-024] Memory Corruption vulnerability in DXE driver

Summary

Binarly REsearch Team has discovered a lack of validation on output buffer leads to OOB Write operations during GIF file processing in AMI firmware.

Vulnerability Information

 
• BINARLY internal vulnerability identifier: BRLY-LOGOFAIL-2023-024  
• 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 REsearch 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:

__int64 sub_5B970()
{
  int v0; // ecx
  int v1; // r14d
  int v2; // ebx
  int v3; // r15d
  int v4; // r12d
  int v5; // edi
  int v6; // ebp
  __int64 v7; // rcx
  int v8; // r10d
  int v9; // esi
  __int64 v10; // rdi
  char v11; // r13
  void *v12; // rdx
  int v13; // eax
  int v14; // r11d
  unsigned __int8 v15; // cl
  unsigned int v17; // [rsp+60h] [rbp+8h]
  int v18; // [rsp+68h] [rbp+10h]

  if ( dword_94FF4 )
  {
    --dword_94FF4;
    v0 = *qword_8CB68++;
    if ( (v0 - 2) > 7 )
      return 4294967293i64;
    dword_8CB88 = 0;
    dword_95018 = 0;
    v1 = v0 + 1;
    v17 = v0 + 1;
    dword_94BA0 = v0 + 1;
    v2 = 1 << (v0 + 1);
    v3 = 1 << v0;
    v18 = 1 << v0;
    dword_8CB78 = 1 << v0;
    v4 = (1 << v0) + 2;
    dword_95024 = v2;
    v5 = (1 << v0) + 1;
    dword_94BA8 = v4;
    dword_8CB90 = v5;
    v6 = v4;
    dword_95014 = v4;
    dword_94BA4 = 512;
    dword_95020 = (sub_5B7E8)();
    v8 = dword_95020;
    if ( dword_95020 == v5 )
      return 0i64;
    v9 = dword_9501C;
    v10 = 0i64;
    v11 = dword_94BB4;
    while ( 1 )
    {
      v12 = &GifCodes;
      if ( dword_8CB8C )
        break;
      if ( v8 == v3 )
      {
        v3 = v18;
        v1 = v17;
        v2 = 1 << v17;
        dword_94BA0 = v17;
        v4 = v18 + 2;
        dword_8CB78 = v18;
        dword_94BA8 = v18 + 2;
        dword_8CB90 = v18 + 1;
        v6 = v18 + 2;
        dword_95014 = v18 + 2;
        dword_95024 = 1 << v17;
        v13 = sub_5B7E8(v17, &GifCodes);
        v9 = v13;
        dword_95020 = v13;
        if ( dword_8CB8C )
          return 4294967292i64;
        dword_9501C = v13;
        dword_94FF0 = v13;
        v11 = v13;
        dword_94BB4 = v13;
        EmitPixel(v13);
      }
      else
      {
        dword_8CB74 = v8;
        v14 = v8;
        if ( v8 >= v6 )
        {
          v8 = v9;
          *(&GifCodes + 8 * v10 + 5) = v11;
          goto LABEL_12;
        }
        while ( v8 >= v4 )
        {
          v7 = v8;
          // BRLY-LOGOFAIL-2023-024
          *(&GifCodes + 8 * v10 + 5) = *(&GifCodes + 8 * v8 + 4);
          v8 = *(&GifCodes + 2 * v8);
LABEL_12:
          ++v10;
        }
        *(&GifCodes + 8 * v10 + 5) = v8;
        v11 = v8;
        ++v10;
        dword_94BB4 = v8;
        dword_94FF0 = v8;
        if ( v10 > 0 )
        {
          do
          {
            v15 = *(&GifCodes + 8 * v10-- - 3);
            EmitPixel(v15);
          }
          while ( v10 > 0 );
          v12 = &GifCodes;
        }
        if ( v6 <= 4095 )
        {
          *(&GifCodes + 8 * v6 + 4) = v8;
          *(&GifCodes + 2 * v6) = v9;
        }
        ++v6;
        dword_9501C = v14;
        dword_95014 = v6;
        v9 = v14;
        if ( v6 >= v2 && v1 < 12 )
        {
          ++v1;
          v2 *= 2;
          dword_94BA0 = v1;
          dword_95024 = v2;
        }
      }
      v8 = sub_5B7E8(v7, v12);
      dword_95020 = v8;
      if ( v8 == v3 + 1 )
        return 0i64;
    }
  }
  return 4294967292i64;
}

As we can see from the pseudocode, the GIF parser in AMI firmware uses a statically allocated array called GifCodes to decode the GIF image data. However this array is used without bounds checking, thus allowing the attacker to trigger overflow on global data.

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