[BRLY-LOGOFAIL-2023-017] Multiple vulnerabilities in image parsing functions can be exploited by an attacker with local access

Summary

Binarly REsearch Team has discovered a lack of checks on array index which leads to OOB Write operations while decoding Huffman tables during PNG file processing in AMI firmware

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-LOGOFAIL-2023-017
• 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:

unsigned __int64 __fastcall HuffmanTablesDecoder(
        unsigned int *a1,
        _DWORD *a2,
        _DWORD *a3,
        __int64 **a4,
        _QWORD *a5,
        _QWORD *a6,
        _QWORD *a7,
        __int64 *ArrayPtr,
        __int64 a9,
        __int64 a10,
        __int64 a11,
        __int64 a12)
{
  _DWORD *v14; // rbx
  unsigned int v15; // esi
  __int64 v16; // rdx
  __int64 v17; // rcx
  __int64 v18; // r8
  __int64 v19; // rdx
  __int64 v20; // rcx
  __int64 v21; // r8
  int Bits; // eax
  unsigned int v23; // eax
  __int64 *v24; // rbx
  __int64 v25; // rdi
  int v26; // eax
  __int64 v27; // rcx
  __int64 v28; // rdx
  __int64 v29; // rdi
  int v31; // r14d
  unsigned int v32; // r14d
  __int64 v33; // rdx
  __int64 v34; // r8
  int *v35; // r11
  int v36; // ecx
  __int64 v37; // rax
  int i; // eax
  __int64 v39; // r8
  int v40; // ecx
  int j; // eax
  __int64 v42; // rcx
  int k; // eax
  __int64 v44; // rcx
  __int64 v45[9]; // [rsp+20h] [rbp-E0h] BYREF
  int v46; // [rsp+68h] [rbp-98h]
  int v47[20]; // [rsp+70h] [rbp-90h] BYREF
  char v48[128]; // [rsp+C0h] [rbp-40h] BYREF
  int v51; // [rsp+190h] [rbp+90h]

  *a2 = 0;
  v14 = a2;
  *a3 = 0;
  v15 = 0;
  *a1 = 0;
  v45[0] = 0x1100000010i64;
  v45[1] = 18i64;
  v45[2] = 0x700000008i64;
  v45[3] = 0x600000009i64;
  v45[4] = 0x50000000Ai64;
  v45[5] = 0x40000000Bi64;
  v45[6] = 0x30000000Ci64;
  v45[7] = 0x20000000Di64;
  v45[8] = 0x10000000Ei64;
  v46 = 15;
  *a1 = ReadBits(a10, a11, a12, 5u);
  *v14 = ReadBits(v17, v16, v18, 5u);
  Bits = ReadBits(v20, v19, v21, 4u);
  *a3 = Bits;
  LODWORD(v14) = Bits;
  sub_7D1D0(v47, 0i64, 76i64);
  v23 = v14 + 4;
  if ( v14 != -4 )
  {
    v24 = v45;
    v25 = v23;
    do
    {
      v26 = ReadBits(a10, a11, a12, 3u);
      v27 = *v24;
      v24 = (v24 + 4);
      v47[v27] = v26;
      --v25;
    }
    while ( v25 );
  }
  sub_5BC44(v48, v45, 19i64, v47);
  v28 = *a1;
  *a4 = ArrayPtr;
  *a5 = a9;
  *a6 = ArrayPtr + 4 * v28 + 1028;
  *a7 = a9 + 1028 + 4 * v28;
  v29 = sub_5C150(19i64, v48, v45);
  if ( !v29 )
    return 0x8000000000000015ui64;
  v31 = *a1;
  v51 = v31;
  if ( v31 + *a2 + 258 )
  {
    v32 = v31 + *a2 + 258;
    do
    {
      if ( sub_5BBD8(a10, a11, a12) )
      {
        if ( *(v35 + 2) )
          v35 = *(v35 + 2);
      }
      else if ( *(v35 + 1) )
      {
        v35 = *(v35 + 1);
      }
      if ( !*(v35 + 1) && !*(v35 + 2) )
      {
        v36 = *v35;
        if ( *v35 > 0xF )
        {
          switch ( v36 )
          {
            case 16:
              for ( i = ReadBits(a10, v33, v34, 2u) + 3; i; --i )
              {
                v39 = v15;
                v40 = *(ArrayPtr + v15++ - 1);
                *(ArrayPtr + v39) = v40;
              }
              break;
            case 17:
              for ( j = ReadBits(a10, v33, v34, 3u) + 3; j; --j )
              {
                v42 = v15++;
                *(ArrayPtr + v42) = 0;
              }
              break;
            case 18:
              for ( k = ReadBits(a10, v33, v34, 7u) + 11; k; --k )
              {
                // BRLY-LOGOFAIL-2023-017: v15 could grow bigger than 322, thus writing OOB on the heap
                v44 = v15++;
                *(ArrayPtr + v44) = 0;
              }
              break;
          }
        }
        else
        {
          v37 = v15++;
          *(ArrayPtr + v37) = v36;
        }
      }
    }
    while ( v15 < v32 );
    v31 = v51;
  }
  sub_5BC44(*a4, *a5, (v31 + 257), *a4);
  sub_5BC44(*a6, *a7, (*a2 + 1), *a6);
  sub_5C208(v29);
  return 0i64;
}

As we can see from the pseudocode, the variable v15 and its copy v42 is used to access the array pointed by the variable ArrayPtr. This array is allocated with a fixed size of 0x508 here:

...
ArrayPtr = AllocateZeroPool(0x508ui64);
v35 = AllocateZeroPool(0x508ui64);
v9 = 0i64;
v60 = v35;
v36 = v35;
if (... HuffmanTablesDecoder(&v69, &v70, &v72, &v74, &v73, v76, &v75, ArrayPtr, v35, a2, &v78, &v79)...)
...    

However, since nExtr is used without any checks it allows the attacker to write after the end of ArrayPtr.

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