[BRLY-2022-121] Memory contents leak / information disclosure vulnerability in DXE driver on Dell platform.

Summary

BINARLY efiXplorer team has discovered a memory contents leak / information disclosure vulnerability that allows a potential attacker to dump stack memory or global memory into an NVRAM variable. This in turn could help building a successful attack vector based on exploiting a memory corruption vulnerability.

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-2022-121
• Dell PSIRT assigned CVE identifier: CVE-2023-28029
• DSA identifier: DSA-2023-099
• CVSS v3.1: 4.9 Medium AV:P/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N

Affected Dell firmware with confirmed impact by Binarly team

Potential impact

An attacker with high physical access can exploit this vulnerability to read the contents of stack memory or global memory. This information could help with explotation of other vulnerabilities in DXE 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 Precision 7920 Tower's firmware (version: 0.2.26.1, module sha256: 52fbfe822173bdecbaa527df3f4270c7327db85fcf2d5a1779cb82c9b2a28c45) as an example.

The following code in the module actually allows leaking memory:

• a call to a gRT->GetVariable() offset: 0x28bf
• a call to a gRT->SetVariable() offset: 0x28f6

__int64 sub_2608()
{
  char v0; // bl
  char v1; // di
  unsigned __int8 v2; // bl
  __int64 v3; // rax
  int v4; // edx
  __int64 result; // rax
  char v6; // al
  int v7; // [rsp+30h] [rbp-9E8h] BYREF
  __int16 v8; // [rsp+34h] [rbp-9E4h]
  __int16 v9; // [rsp+36h] [rbp-9E2h]
  char v10; // [rsp+38h] [rbp-9E0h]
  char v11; // [rsp+39h] [rbp-9DFh]
  char v12; // [rsp+3Ah] [rbp-9DEh]
  char v13; // [rsp+3Bh] [rbp-9DDh]
  char v14; // [rsp+3Ch] [rbp-9DCh]
  char v15; // [rsp+3Dh] [rbp-9DBh]
  char v16; // [rsp+3Eh] [rbp-9DAh]
  char v17; // [rsp+3Fh] [rbp-9D9h]
  int v18; // [rsp+40h] [rbp-9D8h] BYREF
  __int16 v19; // [rsp+44h] [rbp-9D4h]
  __int16 v20; // [rsp+46h] [rbp-9D2h]
  char v21; // [rsp+48h] [rbp-9D0h]
  char v22; // [rsp+49h] [rbp-9CFh]
  char v23; // [rsp+4Ah] [rbp-9CEh]
  char v24; // [rsp+4Bh] [rbp-9CDh]
  char v25; // [rsp+4Ch] [rbp-9CCh]
  char v26; // [rsp+4Dh] [rbp-9CBh]
  char v27; // [rsp+4Eh] [rbp-9CAh]
  char v28; // [rsp+4Fh] [rbp-9C9h]
  int v29; // [rsp+50h] [rbp-9C8h] BYREF
  unsigned int v30; // [rsp+54h] [rbp-9C4h] BYREF
  unsigned int v31; // [rsp+58h] [rbp-9C0h] BYREF
  unsigned int v32; // [rsp+5Ch] [rbp-9BCh] BYREF
  __int64 v33; // [rsp+60h] [rbp-9B8h] BYREF
  __int64 v34; // [rsp+68h] [rbp-9B0h] BYREF
  _QWORD v35[2]; // [rsp+70h] [rbp-9A8h] BYREF
  __int64 v36; // [rsp+80h] [rbp-998h] BYREF
  _BYTE v37[763]; // [rsp+90h] [rbp-988h] BYREF
  char v38; // [rsp+38Bh] [rbp-68Dh]
  char v39; // [rsp+3A0h] [rbp-678h]
  char v40; // [rsp+3A1h] [rbp-677h]
  char v41; // [rsp+3EEh] [rbp-62Ah]
  char v42; // [rsp+444h] [rbp-5D4h]
  char v43; // [rsp+470h] [rbp-5A8h]
  _BYTE v44[632]; // [rsp+7A0h] [rbp-278h] BYREF
  char v45; // [rsp+A20h] [rbp+8h] BYREF
  int v46; // [rsp+A28h] [rbp+10h] BYREF
  unsigned int v47; // [rsp+A30h] [rbp+18h] BYREF
  unsigned int v48; // [rsp+A38h] [rbp+20h] BYREF

  v8 = 5729;
  v9 = 18403;
  v19 = 26188;
  v20 = 19799;
  v35[0] = 0i64;
  v29 = 0;
  v36 = 1805i64;
  v7 = 758045968;
  v10 = -67;
  v11 = -1;
  v12 = 88;
  v13 = 31;
  v14 = 42;
  v15 = 99;
  v16 = -20;
  v17 = 13;
  v18 = 1029781824;
  v21 = -114;
  v22 = -2;
  v23 = 54;
  v24 = 61;
  v25 = -77;
  v26 = -56;
  v27 = -18;
  v28 = -14;
  v45 = 0;
  sub_19544(17170444, 0i64, 2i64, 0i64, (int *)&v47);
  v47 >>= 1;
  v0 = v47;
  sub_19544(17170445, 0i64, 2i64, 0i64, (int *)&v48);
  v48 >>= 1;
  v1 = v0 | (2 * v48);
  if ( ((__int64 (__fastcall *)(EFI_GUID *, _QWORD, _QWORD *))gBS->LocateProtocol)(&UNKNOWN_PROTOCOL_GUID_3, 0i64, v35) >= 0 )
    (*(void (__fastcall **)(int *, __int64, _QWORD))(v35[0] + 8i64))(&v29, 5i64, 0i64);
  v2 = 0;
  if ( v29 == 1 )
    v2 = 32;
  v34 = 4i64;
  v3 = ((__int64 (__fastcall *)(const __int16 *, int *, _QWORD, __int64 *, int *))gRT->GetVariable)(
         L"LastModeState",
         &v7,
         0i64,
         &v34,
         &v46);
  v4 = v46;
  if ( v3 < 0 )
    v4 = 0;
  v46 = v4;
  result = v4 & 0x20;
  if ( (_DWORD)result != v2 )
  {
    v31 = v2 | v4 & 0xFFFFFFDF;
    v34 = 4i64;
    result = ((__int64 (__fastcall *)(const __int16 *, int *, __int64, __int64, unsigned int *))gRT->SetVariable)(
               L"LastModeState",
               &v7,
               7i64,
               4i64,
               &v31);
    LOBYTE(v4) = v46;
  }
  if ( v2 )
  {
    if ( (v4 & 0x20) == 0 )
    {
      v45 = 1;
      ((void (__fastcall *)(const __int16 *, int *, __int64, __int64, char *))gRT->SetVariable)(
        L"DFMMRecordFlag",
        &v18,
        3i64,
        1i64,
        &v45);
      result = ((__int64 (__fastcall *)(const __int16 *, EFI_GUID *, unsigned int *, __int64 *, _BYTE *))gRT->GetVariable)(
                 L"Setup",
                 &EFI_SETUP_VARIABLE_GUID,
                 &v32,
                 &v36,
                 v37);
      if ( result >= 0 )
      {
        v39 = 2;
        v40 = 0;
        v33 = 563i64;
        ((void (__fastcall *)(const __int16 *, EFI_GUID *, unsigned int *, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
          L"IntelSetup",
          &EFI_SETUP_VARIABLE_GUID_0,
          &v30,
          &v33,
          v44);
        v44[108] = 1;
        ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64, _BYTE *))gRT->SetVariable)(// <= second call
          L"IntelSetup",
          &EFI_SETUP_VARIABLE_GUID_0,
          v30,
          v33,
          v44);
        v6 = v38;
        if ( !v1 )
          v6 = 1;
        v38 = v6;
        v37[755] = 1;
        v37[756] = 1;
        v37[757] = 1;
        v37[758] = 1;
        v37[759] = 1;
        v37[760] = 1;
        v37[761] = 1;
        v37[762] = 1;
        v43 = 2;
        v42 = 1;
        v41 = 0;
        v37[651] = 1;
        v37[652] = 1;
        memset(&v37[655], 1, 33);
        ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64, _BYTE *))gRT->SetVariable)(
          L"Setup",
          &EFI_SETUP_VARIABLE_GUID,
          v32,
          1805i64,
          v37);
        ((void (__fastcall *)(_QWORD, _QWORD, _QWORD, _QWORD))gRT->ResetSystem)(0i64, 0i64, 0i64, 0i64);
        v35[1] = 1i64;
        while ( 1 )
          ;
      }
    }
  }
  return result;
}

The gRT->SetVariable() service is called with the DataSize as an argument, which will be overwritten inside the gRT->GetVariable() service if the length of IntelSetup NVRAM variable is greater than 563.

Thus, a potential attacker can dump X - 563 bytes from the stack (or global memory) into IntelSetup NVRAM variable by setting IntelSetup NVRAM variable's size to X > 563.

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

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