[BRLY-LOGOFAIL-2023-004] Memory Corruption vulnerability in DXE driver

Summary

Binarly REsearch Team has discovered a multiple OOB Read/Write vulnerabilities in Insyde firmware related to lack of validation in the LZW decoder routine in the GifDecoderDxe module.

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-LOGOFAIL-2023-004  
• Insyde PSIRT assigned CVE identifier: CVE-2023-40238  
• 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 __fastcall DecodeLZW(
        char *Image,
        unsigned __int64 a2,
        char a3,
        __int64 a4,
        unsigned __int16 a5,
        unsigned __int16 a6,
        __int64 a7)
{
  HeapStruct *v7; // r13
  char Value; // cl
  char *v10; // r11
  unsigned __int16 Bound; // bx
  unsigned __int8 v12; // r9
  __int16 v13; // di
  unsigned __int16 v14; // r12
  unsigned __int8 v15; // si
  unsigned int v16; // r10d
  unsigned __int16 v17; // r15
  unsigned __int16 v18; // r8
  unsigned __int16 Index; // cx
  HeapStruct *HeapArrayEntry; // rax
  unsigned __int16 v21; // bp
  _BYTE *v22; // r14
  unsigned __int64 v23; // rax
  char v24; // cl
  unsigned __int16 v25; // r11
  __int16 v26; // r9
  unsigned __int16 v27; // ax
  unsigned __int16 v28; // ax
  __int64 v29; // rdx
  __int64 v30; // rax
  __int64 v31; // rdx
  char v33; // [rsp+0h] [rbp-68h]
  unsigned __int8 v34; // [rsp+1h] [rbp-67h]
  unsigned __int16 v35; // [rsp+2h] [rbp-66h]
  __int16 v36; // [rsp+4h] [rbp-64h]
  __int16 v37; // [rsp+6h] [rbp-62h]
  unsigned __int16 v38; // [rsp+8h] [rbp-60h]
  unsigned __int16 v39; // [rsp+10h] [rbp-58h]
  char *v40; // [rsp+70h] [rbp+8h]

  v7 = HeapArray;
  Value = *Image;
  v10 = Image + 1;
  Bound = 1 << Value;
  v40 = v10;
  v39 = Bound;
  v12 = Value + 1;
  v36 = -1;
  v37 = (1 << Value) + 1;
  v13 = -1;
  v34 = Value + 1;
  v38 = (1 << Value) + 2;
  v14 = v38;
  v35 = v38;
  v15 = Value + 1;
  v33 = Value + 1;
  v16 = 0;
  v17 = 0;
  v18 = 0;
  Index = 0;
  if ( Bound )
  {
    HeapArrayEntry = HeapArray;
    // BRLY-LOGOFAIL-2023-004
    do
    {
      HeapArrayEntry->field_2 = Index++;
      HeapArrayEntry->field_0 = -1;
      HeapArrayEntry = (HeapArrayEntry + 4);
    }
    while ( Index < Bound );
    v7 = HeapArray;
  }
  if ( v12 >> 3 <= a2 )
  {
    v21 = a6;
    v22 = qword_1D50;
    do
    {
      v23 = v16 >> 3;
      v24 = v16 & 7;
      v16 += v15;
      v25 = ((1 << v15) - 1) & (*&v10[v23] >> v24);
      if ( v25 == v37 )
        return v16;
      if ( v25 == Bound )
      {
        v14 = v38;
        v15 = v12;
        v35 = v38;
        v13 = Bound;
        v33 = v12;
        v36 = Bound;
        goto LABEL_40;
      }
      if ( v18 == v21 )
        return v16;
      v26 = -1;
      if ( v25 >= v14 )
      {
        if ( v13 == Bound )
          goto LABEL_44;
        v26 = 0;
        v28 = v13;
        if ( v13 != -1 )
        {
          do
          {
            v22[++v26] = *(&v7->field_2 + 4 * v28);
            v28 = *(&v7->field_0 + 2 * v28);
          }
          while ( v28 != 0xFFFF );
          v15 = v33;
          v21 = a6;
        }
        *v22 = v22[v26];
      }
      else
      {
        v27 = v25;
        if ( v25 != 0xFFFF )
        {
          do
          {
            v22[++v26] = *(&v7->field_2 + 4 * v27);
            v27 = *(&v7->field_0 + 2 * v27);
          }
          while ( v27 != 0xFFFF );
          v21 = a6;
        }
        if ( v13 == Bound )
          goto LABEL_23;
      }
      v29 = v14++;
      v35 = v14;
      *(&v7->field_0 + 2 * v29) = v13;
      *(&v7->field_2 + 4 * v29) = v22[v26];
LABEL_23:
      if ( v26 >= 0 )
      {
        do
        {
          v30 = v26--;
          v31 = v22[v30];
          LODWORD(v30) = v17++;
          *(a7 + 4i64 * (v30 + a5 * v18)) = *(a4 + 4 * v31);
          if ( v17 == a5 )
          {
            if ( a3 )
            {
              if ( (v18 & 7) != 0 )
              {
                if ( (v18 & 3) != 0 )
                {
                  if ( (v18 & 1) != 0 )
                  {
                    v18 += 2;
                  }
                  else
                  {
                    v18 += 4;
                    if ( v18 >= v21 )
                      v18 = 1;
                  }
                }
                else
                {
                  v18 += 8;
                  if ( v18 >= v21 )
                    v18 = 2;
                }
              }
              else
              {
                v18 += 8;
                if ( v18 >= v21 )
                  v18 = 4;
              }
            }
            else
            {
              ++v18;
            }
            v17 = 0;
            if ( v18 == v21 )
              break;
          }
        }
        while ( v26 >= 0 );
        Bound = v39;
        v13 = v36;
        v15 = v33;
        v14 = v35;
        v7 = HeapArray;
      }
LABEL_40:
      if ( v14 < 1 << v15 )
        goto LABEL_43;
      if ( v15 < 0xCu )
      {
        v33 = ++v15;
LABEL_43:
        v13 = v25;
        v36 = v25;
      }
LABEL_44:
      v12 = v34;
      v10 = v40;
    }
    while ( (v16 + v15) >> 3 <= a2 );
  }
  return v16;
}

As we can see from the pseudocode:

• Value is controllable and may take values from 0x00 to 0xff  
• When Value = 15, Bound will take max value ( 32768)  
• HeapArray have 4096 elements, so heap overflow will happen here:  

HeapArrayEntry = HeapArray;
do
{
  // Vulnerability OOB Write here
  HeapArrayEntry->field_2 = Index++;
  HeapArrayEntry->field_0 = -1;
  HeapArrayEntry = (HeapArrayEntry + 4);
}
while ( Index < Bound );

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