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-2022-165
• Dell PSIRT assigned CVE identifier: CVE-2023-28054
• DSA identifier: DSA-2023-099
• CVSS v3.1: 6.0 Medium AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N

Affected Dell firmware with confirmed impact by Binarly team

Product	Firmware version	CPU	Module name	Module GUID	Module SHA256
Precision 7920 Tower	0.2.26.1	Intel	F80E66A2-1A2C-415B-9B9C-066C1F04B626	f80e66a2-1a2c-415b-9b9c-066c1f04b626	cb6291081bba88deab578139ec4dabc313cf29d6fa2a1ca8254cd19ea56c2867

Potential impact

An attacker with high local 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: cb6291081bba88deab578139ec4dabc313cf29d6fa2a1ca8254cd19ea56c2867) as an example.

The following code in the module actually allows leaking memory:

• a call to a gRT->GetVariable() offset: 0x1206
• a call to a gRT->SetVariable() offset: 0x123d

__int64 sub_B70()
{
  char v0; // bp
  char v1; // r13
  char v2; // r12
  __int64 v3; // rax
  __int64 result; // rax
  char v5; // r9
  unsigned __int8 v6; // bl
  unsigned __int8 v7; // cl
  char v8; // dl
  int v9; // ebx
  int v10; // ecx
  char v11; // dl
  char v12; // cl
  unsigned __int8 v13; // cl
  int v14; // esi
  int *v15; // rbx
  int v16; // edi
  char v17; // al
  __int64 v18; // rbx
  _BYTE v19[4]; // [rsp+30h] [rbp-19D8h]
  unsigned int v20; // [rsp+34h] [rbp-19D4h] BYREF
  char v21[4]; // [rsp+38h] [rbp-19D0h] BYREF
  unsigned int v22; // [rsp+3Ch] [rbp-19CCh] BYREF
  __int64 v23; // [rsp+40h] [rbp-19C8h] BYREF
  __int64 v24; // [rsp+48h] [rbp-19C0h] BYREF
  __int64 v25; // [rsp+50h] [rbp-19B8h] BYREF
  __int64 v26; // [rsp+58h] [rbp-19B0h] BYREF
  _QWORD v27[2]; // [rsp+60h] [rbp-19A8h] BYREF
  __int64 v28; // [rsp+70h] [rbp-1998h] BYREF
  EFI_EVENT v29; // [rsp+78h] [rbp-1990h] BYREF
  _BYTE v30[6536]; // [rsp+80h] [rbp-1988h] BYREF
  int *v31; // [rsp+1A20h] [rbp+18h] BYREF
  char v32; // [rsp+1A28h] [rbp+20h] BYREF

  v23 = 0xFFFFFFFFi64;
  v20 = 0;
  v25 = 0i64;
  v0 = 0;
  v1 = 0;
  v2 = 0;
  v24 = 6475i64;
  (gBS->AllocatePages)(1i64, 10i64, 1i64, &v23);
  qword_80D0 = v23;
  (gBS->SetMem)(v23, 29i64, 0i64);
  gUnknownProtocol = qword_80D0;
  (gBS->InstallProtocolInterface)(&v25, &UNKNOWN_PROTOCOL_GUID, 0i64, &gUnknownProtocol);
  if ( gST->Hdr.Revision >= 0x20000 )
    sub_1F50(&v29);
  if ( (sub_1EE8(&TCG_EFI_HOB_LIST_GUID, &qword_87F8) & 0x8000000000000000ui64) != 0i64 )
    return 0x800000000000000Eui64;
  v3 = qword_87F8;
  if ( !qword_87F8 )
    return 0x800000000000000Eui64;
  while ( 1 )
  {
    if ( *v3 == 0xFFFF )
    {
      v3 = 0i64;
    }
    else if ( *v3 != 4 )
    {
      goto LABEL_7;
    }
    if ( !v3 || *&ITBT_INFO_HOB_GUID.Data1 == *(v3 + 8) && *ITBT_INFO_HOB_GUID.Data4 == *(v3 + 16) )
      break;
LABEL_7:
    v3 += *(v3 + 2);
  }
  qword_87F8 = v3;
  if ( !v3 )
    return 0x800000000000000Eui64;
  v28 = 1805i64;
  result = (gRT->GetVariable)(L"Setup", &EFI_SETUP_VARIABLE_GUID_1, &v20, &v28, &unk_80E0);
  if ( result >= 0 )
  {
    (gBS->CreateEvent)(&VariableNameSize, 16i64, sub_A40);
    (gBS->RegisterProtocolNotify)(&UNKNOWN_PROTOCOL_GUID_0, v27[1], &Registration);
    sub_490();
    v5 = byte_8171;
    if ( byte_8171 == -1 )
    {
      v19[0] = 9;
      v19[1] = 22;
      v19[2] = 26;
      v6 = 0;
      while ( 1 )
      {
        v7 = v19[v6];
        if ( v7 )
        {
          if ( sub_1CD8(v7, v21, &v32, &v31) >= 0 )
            break;
        }
        if ( ++v6 >= 3u )
        {
          byte_8171 = 0;
          byte_87F3 = 0;
          sub_9FC(&byte_87F0, 0);
          break;
        }
      }
      v5 = byte_8171;
    }
    v8 = byte_5901;
    if ( byte_87F2 != *(qword_87F8 + 56) )
      v8 = 1;
    byte_5901 = v8;
    if ( !byte_5900 )
      goto LABEL_35;
    if ( !v5 )
      goto LABEL_35;
    byte_5901 = 1;
    if ( v5 != -1 && sub_3AB4(v5, 1, 1) < 0 )
      goto LABEL_35;
    v26 = 1805i64;
    result = (gRT->GetVariable)(L"Setup", &EFI_SETUP_VARIABLE_GUID_1, &v20, &v26, &unk_80E0);
    if ( result >= 0 )
    {
      if ( byte_8171 == -1 )
      {
        if ( sub_9FC(&byte_87F0, 2) >= 0 )
        {
          byte_5901 = 0;
          goto LABEL_34;
        }
      }
      else if ( !sub_964(*(qword_87F8 + 53), *(qword_87F8 + 54), *(qword_87F8 + 55)) )
      {
LABEL_34:
        v2 = 1;
        v0 = 1;
      }
LABEL_35:
      v9 = dword_87F4;
      if ( dword_87F4 < 2 )
        goto LABEL_65;
      if ( byte_5900 )
        goto LABEL_65;
      v10 = *(sub_2024() + 12);
      if ( v10 == 16 || v10 == 17 || v10 == 5 || v10 == 18 || v10 == 32 )
        goto LABEL_65;
      if ( v9 == 2 )
      {
        sub_758(1, qword_87F8);
        v11 = *(qword_87F8 + 52);
        if ( v11 && sub_24C4(255, v11) >= 0 )
        {
          v12 = *(qword_87F8 + 52);
          byte_5901 = 1;
          byte_87F3 = v12;
          sub_9FC(&byte_87F0, 3);
          goto LABEL_52;
        }
      }
      else if ( v9 == 3 )
      {
        sub_758(0, qword_87F8);
        if ( *(qword_87F8 + 52) != byte_87F3 )
        {
          dword_87F4 = 1;
          if ( byte_87F3 == -1 || !byte_87F3 || sub_3AB4(byte_87F3, 0, 0) >= 0 )
          {
            byte_87F3 = 0;
            sub_9FC(&byte_87F0, 2);
            v2 = 1;
LABEL_52:
            v0 = 1;
          }
        }
      }
      if ( !v0
        || (v27[0] = 1805i64,
            result = (gRT->GetVariable)(L"Setup", &EFI_SETUP_VARIABLE_GUID_1, &v20, v27, &unk_80E0),
            result >= 0) )
      {
        if ( !byte_5901 )
          goto LABEL_67;
        if ( !*(qword_87F8 + 52) )
          goto LABEL_67;
        v13 = *(qword_87F8 + 53);
        if ( !v13 && !*(qword_87F8 + 54) && !*(qword_87F8 + 55) )
          goto LABEL_67;
LABEL_65:
        LOBYTE(v14) = *(sub_1F98(v13, *(qword_87F8 + 54), *(qword_87F8 + 55)) + 25);
        if ( v14 )
        {
          v15 = v31;
          v16 = v31;
        }
        else
        {
          v14 = sub_12E0(*(qword_87F8 + 53));
          v15 = (sub_1F98(*(qword_87F8 + 53), *(qword_87F8 + 54), *(qword_87F8 + 55)) + 24);
          v16 = *v15;
          v1 = 1;
          *v15 = *(qword_87F8 + 53) + 65792 * v14;
        }
        sub_1498(*(qword_87F8 + 53), *(qword_87F8 + 54), *(qword_87F8 + 55));
        v17 = sub_1968(
                *(qword_87F8 + 56),
                v14,
                *(qword_87F8 + 49),
                *(qword_87F8 + 25),
                *(qword_87F8 + 29),
                *(qword_87F8 + 50));
        if ( v1 )
          *v15 = v16;
        if ( v17 != -1 )
        {
          byte_87F2 = v17;
          (gRT->SetVariable)(L"TbtHRStatusVar", &VendorGuid, 7i64, DataSize, &byte_87F0);
        }
        else
        {
LABEL_67:
          *(qword_87F8 + 56) = byte_87F2;
          byte_8169 = byte_87F2;
        }
        if ( byte_8158 == 1 && byte_8160 == 2 && byte_87F3 && *(qword_87F8 + 58) == 1 && *(qword_87F8 + 70) < 8u )
        {
          byte_8178 = 8;
          *(qword_87F8 + 70) = 8;
        }
        if ( byte_841F )
        {
          byte_812D = 1;
          (gRT->GetVariable)(                   // <= first call (we can rewrite DataSize here)
            L"SocketIioConfig",
            &EFI_SOCKET_IIO_VARIABLE_GUID,
            &v22,
            &v24,
            v30);
          v30[4024] = 1;
          (gRT->SetVariable)(                   // <= second call
            L"SocketIioConfig",
            &EFI_SOCKET_IIO_VARIABLE_GUID,
            v22,
            v24,
            v30);
        }
        v18 = (gRT->SetVariable)(L"Setup", &EFI_SETUP_VARIABLE_GUID_1, v20, 1805i64, &unk_80E0);
        if ( v0 )
        {
          __outbyte(0xCF9u, v2 != 0 ? 14 : 6);
          while ( 1 )
            ;
        }
        if ( *(qword_87F8 + 52) && !sub_964(*(qword_87F8 + 53), *(qword_87F8 + 54), *(qword_87F8 + 55)) )
          *(qword_87F8 + 52) = 0;
        return v18;
      }
    }
  }
  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 SocketIioConfig NVRAM variable is greater than 6475.

Thus, a potential attacker can dump X - 6475 bytes from the stack (or global memory) into SocketIioConfig NVRAM variable by setting SocketIioConfig NVRAM variable's size to X > 6475.

To fix this vulnerability the DataSize must be re-initialized with the size of SocketIioConfig 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.

Disclosure Activity	Date (YYYY-mm-dd)
Dell PSIRT is notified	2022-12-29
Dell PSIRT confirmed reported issue	2023-03-16
Dell PSIRT assigned CVE number	2023-06-15
Dell PSIRT provide patch release	2023-06-15
BINARLY public disclosure date	2023-06-21

Acknowledgements

BINARLY efiXplorer team