[BRLY-2022-065] Stack buffer overflow vulnerability leads to arbitrary code execution in DXE driver on multiple Dell platforms.

Summary

BINARLY efiXplorer team has discovered a stack overflow vulnerability that allows a potential attacker to access UEFI DXE driver and execute arbitrary code.

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-2022-065
• Dell PSIRT assigned CVE identifier: CVE-2023-32466
• DSA identifier: DSA-2023-225/DSA-2023-225
• CVSS v3.1: 8.2 High AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Affected Dell firmware with confirmed impact by Binarly team

Potential impact

An attacker with high local access can exploit this vulnerability to elevate privileges from ring 3 or ring 0 (depends 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

Let's take Edge Gateway 3200's firmware (version: 103, module sha256: 99e00b3febba1763a7ff3f1eb043872506a00032ea2166b3611c041f8e56a3bb) as an example.

The following code in the module actually allows to overflow a stack buffer:

• a call to a gRT->GetVariable() offset: 0x10741
• a call to a gRT->GetVariable() offset: 0x10840

void *__fastcall sub_105AC(void *a1)
{
  char v2; // di
  unsigned int v3; // esi
  void *result; // rax
  void *v5; // r12
  __int64 v6; // rdx
  __int64 v7; // rdx
  __int64 v8; // rdx
  unsigned int v9; // ebx
  char *v10; // rsi
  __int64 v11; // r14
  char v12; // al
  char *v13; // rbx
  const __int16 *v14; // rax
  __int64 v15; // rbx
  UINTN v16; // rbx
  bool v17; // zf
  __int64 v18; // rdi
  const __int16 *v19; // rax
  __int16 *v20; // rdx
  const __int16 *v21; // rax
  UINTN v22; // rdi
  __int64 v23; // rdi
  const __int16 *v24; // rax
  __int16 *v25; // rdx
  const __int16 *v26; // rax
  UINTN v27; // rdi
  __int64 v28; // rdi
  const __int16 *v29; // rax
  __int16 *v30; // rdx
  const __int16 *v31; // rax
  UINTN v32; // rdi
  __int64 v33; // r8
  __int16 *v34; // rax
  __int16 *v35; // rdx
  __int16 *v36; // rax
  char v37; // al
  char *v38; // rbx
  char v39; // cl
  const __int16 *v40; // rax
  __int64 v41; // rbx
  UINTN v42; // rbx
  __int64 v43; // rdi
  const __int16 *v44; // rax
  __int16 *v45; // rdx
  const __int16 *v46; // rax
  UINTN v47; // rdi
  __int64 v48; // rdi
  const __int16 *v49; // rax
  __int16 *v50; // rdx
  const __int16 *v51; // rax
  UINTN v52; // rdi
  __int64 v53; // rdi
  const __int16 *v54; // rax
  __int16 *v55; // rdx
  const __int16 *v56; // rax
  UINTN v57; // rdi
  __int64 v58; // r8
  __int16 *v59; // rax
  __int16 *v60; // rdx
  __int16 *v61; // rax
  unsigned int v62; // ebx
  char *p_Destination; // rdi
  __int64 v64; // rsi
  __int64 v65; // [rsp+20h] [rbp-E0h]
  __int64 v66; // [rsp+20h] [rbp-E0h]
  char v67[4]; // [rsp+30h] [rbp-D0h] BYREF
  char v68; // [rsp+34h] [rbp-CCh]
  unsigned int v69; // [rsp+3Ch] [rbp-C4h]
  unsigned int v70; // [rsp+40h] [rbp-C0h]
  EFI_GUID VendorGuid; // [rsp+48h] [rbp-B8h] BYREF
  UINTN v72; // [rsp+60h] [rbp-A0h] BYREF
  UINT32 Attributes; // [rsp+68h] [rbp-98h] BYREF
  UINTN DataSize; // [rsp+70h] [rbp-90h] BYREF
  void *v75; // [rsp+78h] [rbp-88h]
  char Buffer[6]; // [rsp+80h] [rbp-80h] BYREF
  char Destination; // [rsp+86h] [rbp-7Ah] BYREF
  char Data[2784]; // [rsp+180h] [rbp+80h] BYREF
  __int16 Source; // [rsp+C80h] [rbp+B80h] BYREF
  UINT32 v80; // [rsp+C88h] [rbp+B88h] BYREF

  v72 = 20i64;
  v80 = 0;
  DataSize = 2736i64;
  VendorGuid.Data1 = -326642109;
  *&VendorGuid.Data2 = 1270213540;
  *VendorGuid.Data4 = 1044374945;
  v2 = 0;
  *&VendorGuid.Data4[4] = -1458720202;
  v3 = 0;
  result = gRT_0->GetVariable(L"Setup", &VendorGuid, &Attributes, &DataSize, Data);

  if ( result >= 0 )
  {
    if ( gEfiHiiStringProtocol_1
      || (result = gBS_0->LocateProtocol(&EFI_HII_STRING_PROTOCOL_GUID, 0i64, &gEfiHiiStringProtocol_1), result >= 0) )
    {
      result = sub_10348(a1);
      v75 = result;
      v5 = result;
      if ( result )
      {
        if ( !Data[21] && !Data[17] )
        {
          v6 = 7417i64;
          if ( Data[11] )
            v6 = 7418i64;
          sub_10408(a1, v6, 7430i64, result);
          v7 = 7436i64;
          if ( Data[12] != 1 )
            v7 = 7435i64;
          sub_10408(a1, v7, 7431i64, v5);
          v8 = 7441i64;
          if ( Data[13] != 1 )
            v8 = 7442i64;
          sub_10408(a1, v8, 7432i64, v5);
          if ( (gRT_0->GetVariable(L"Tpm12VersionInfo", &PEI_TCG_INTERNAL_FLAGS_GUID, &v80, &v72, v67) & 0x8000000000000000ui64) == 0i64 )
          {
            gBS_0->SetMem(Buffer, 0x80ui64, 0);
            LODWORD(v65) = v69;
            sub_6DC(a1, 7493i64, L"%d.%d", BYTE1(v69), v65);
            gBS_0->SetMem(Buffer, 0x80ui64, 0);
            v9 = v70;
            v10 = Buffer;
            v11 = 4i64;
            do
            {
              Source = v9;
              if ( v9 )
                gBS_0->CopyMem(v10, &Source, 2ui64);
              v10 += 2;
              v9 >>= 8;
              --v11;
            }
            while ( v11 );
            sub_6DC(a1, 7492i64, aS, Buffer);
            v3 = 4;
          }
        }
        result = gRT_0->GetVariable(            // <= second call
                   L"PCRBitmap",
                   &PEI_TCG_INTERNAL_FLAGS_GUID,
                   &v80,
                   &v72,
                   v67);
        if ( result >= 0 )
        {
          gBS_0->SetMem(Buffer, 0x80ui64, 0);
          v12 = v67[0];
          v13 = Buffer;
          if ( (v67[0] & 1) != 0 )
          {
            v14 = L"SHA-1";
            v15 = 0i64;
            do
            {
              ++v14;
              ++v15;
            }
            while ( *v14 );
            v16 = 2 * v15;
            gBS_0->CopyMem(Buffer, L"SHA-1", v16);
            v12 = v67[0];
            v13 = &Buffer[v16];
            v2 = 1;
          }
          if ( (v12 & 2) != 0 )
          {
            v17 = v2 == 0;
            v18 = 0i64;
            if ( v17 )
            {
              v21 = L"SHA256";
              do
              {
                ++v21;
                ++v18;
              }
              while ( *v21 );
              v20 = L"SHA256";
            }
            else
            {
              v19 = L",SHA256";
              do
              {
                ++v19;
                ++v18;
              }
              while ( *v19 );
              v20 = L",SHA256";
            }
            v22 = 2 * v18;
            gBS_0->CopyMem(v13, v20, v22);
            v12 = v67[0];
            v13 += v22;
            v2 = 1;
          }
          if ( (v12 & 4) != 0 )
          {
            v17 = v2 == 0;
            v23 = 0i64;
            if ( v17 )
            {
              v26 = L"SHA384";
              do
              {
                ++v26;
                ++v23;
              }
              while ( *v26 );
              v25 = L"SHA384";
            }
            else
            {
              v24 = L",SHA384";
              do
              {
                ++v24;
                ++v23;
              }
              while ( *v24 );
              v25 = L",SHA384";
            }
            v27 = 2 * v23;
            gBS_0->CopyMem(v13, v25, v27);
            v12 = v67[0];
            v13 += v27;
            v2 = 1;
          }
          if ( (v12 & 8) != 0 )
          {
            v17 = v2 == 0;
            v28 = 0i64;
            if ( v17 )
            {
              v31 = L"SHA512";
              do
              {
                ++v31;
                ++v28;
              }
              while ( *v31 );
              v30 = L"SHA512";
            }
            else
            {
              v29 = L",SHA512";
              do
              {
                ++v29;
                ++v28;
              }
              while ( *v29 );
              v30 = L",SHA512";
            }
            v32 = 2 * v28;
            gBS_0->CopyMem(v13, v30, v32);
            v12 = v67[0];
            v13 += v32;
            v2 = 1;
          }
          if ( (v12 & 0x10) != 0 )
          {
            v33 = 0i64;
            if ( v2 )
            {
              v34 = aSm3;
              do
              {
                ++v34;
                ++v33;
              }
              while ( *v34 );
              v35 = aSm3;
            }
            else
            {
              v36 = aSm3_0;
              do
              {
                ++v36;
                ++v33;
              }
              while ( *v36 );
              v35 = aSm3_0;
            }
            gBS_0->CopyMem(v13, v35, 2 * v33);
          }
          sub_6DC(a1, 7477i64, aS, Buffer);
          gBS_0->SetMem(Buffer, 0x80ui64, 0);
          v37 = v68;
          v38 = Buffer;
          v39 = 0;
          if ( (v68 & 1) != 0 )
          {
            v40 = L"SHA-1";
            v41 = 0i64;
            do
            {
              ++v40;
              ++v41;
            }
            while ( *v40 );
            v42 = 2 * v41;
            gBS_0->CopyMem(Buffer, L"SHA-1", v42);
            v37 = v68;
            v38 = &Buffer[v42];
            v39 = 1;
          }
          if ( (v37 & 2) != 0 )
          {
            v43 = 0i64;
            if ( v39 )
            {
              v44 = L",SHA256";
              do
              {
                ++v44;
                ++v43;
              }
              while ( *v44 );
              v45 = L",SHA256";
            }
            else
            {
              v46 = L"SHA256";
              do
              {
                ++v46;
                ++v43;
              }
              while ( *v46 );
              v45 = L"SHA256";
            }
            v47 = 2 * v43;
            gBS_0->CopyMem(v38, v45, v47);
            v37 = v68;
            v38 += v47;
            v39 = 1;
          }
          if ( (v37 & 4) != 0 )
          {
            v48 = 0i64;
            if ( v39 )
            {
              v49 = L",SHA384";
              do
              {
                ++v49;
                ++v48;
              }
              while ( *v49 );
              v50 = L",SHA384";
            }
            else
            {
              v51 = L"SHA384";
              do
              {
                ++v51;
                ++v48;
              }
              while ( *v51 );
              v50 = L"SHA384";
            }
            v52 = 2 * v48;
            gBS_0->CopyMem(v38, v50, v52);
            v37 = v68;
            v38 += v52;
            v39 = 1;
          }
          if ( (v37 & 8) != 0 )
          {
            v53 = 0i64;
            if ( v39 )
            {
              v54 = L",SHA512";
              do
              {
                ++v54;
                ++v53;
              }
              while ( *v54 );
              v55 = L",SHA512";
            }
            else
            {
              v56 = L"SHA512";
              do
              {
                ++v56;
                ++v53;
              }
              while ( *v56 );
              v55 = L"SHA512";
            }
            v57 = 2 * v53;
            gBS_0->CopyMem(v38, v55, v57);
            v37 = v68;
            v38 += v57;
            v39 = 1;
          }
          if ( (v37 & 0x10) != 0 )
          {
            v58 = 0i64;
            if ( v39 )
            {
              v59 = aSm3;
              do
              {
                ++v59;
                ++v58;
              }
              while ( *v59 );
              v60 = aSm3;
            }
            else
            {
              v61 = aSm3_0;
              do
              {
                ++v61;
                ++v58;
              }
              while ( *v61 );
              v60 = aSm3_0;
            }
            gBS_0->CopyMem(v38, v60, 2 * v58);
          }
          sub_6DC(a1, 7474i64, aS, Buffer);
          gBS_0->SetMem(Buffer, 0x80ui64, 0);
          LODWORD(v66) = v69;
          sub_6DC(a1, 7493i64, L"%d.%d", HIWORD(v69), v66);
          gBS_0->SetMem(Buffer, 0x80ui64, 0);
          v62 = v70;
          p_Destination = &Destination;
          if ( v3 < 4 )
          {
            v64 = 4 - v3;
            do
            {
              Source = v62;
              gBS_0->CopyMem(p_Destination, &Source, 2ui64);
              p_Destination -= 2;
              v62 >>= 8;
              --v64;
            }
            while ( v64 );
            v5 = v75;
          }
          sub_6DC(a1, 7492i64, aS, Buffer);
          return gBS_0->FreePool(v5);
        }
      }
    }
  }
  return result;
}

The DataSize is initialized only once (before the first call to gRT->GetVariable() service).

If the length of Tpm12VersionInfo NVRAM variable is greater than 20, the second call to gRT->GetVariable() service will overflow a stack buffer, which in turn could lead to arbitrary code execution.

To fix this vulnerability the DataSize must be re-initialized with the size of PCRBitmap before calling gRT->GetVariable().

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 efiXplorer team