[BRLY-2022-101] Memory contents leak / information disclosure vulnerability in DXE driver on Dell platform.

June 22, 2023

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-2022-101
Dell PSIRT assigned CVE identifier: CVE-2023-25937
DSA identifier: DSA-2023-099/DSA-2023-204
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

Product	Firmware version	CPU	Module name	Module GUID	Module SHA256
Latitude 3300	0.1.17.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	242a5ea5ff855aed77a41207d3f43546b13a32bb5ceab4e333e7b5f0958afb8a
XPS 8940	0.2.4.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	3194dcc56c37ac93cedb90571bfbc492f1b5e814bf887c59b3cd7e67087bf752
XPS 8940	0.2.4.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	3194dcc56c37ac93cedb90571bfbc492f1b5e814bf887c59b3cd7e67087bf752
Insprion/Vostro 3X8X	0.1.19.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	366d49466dc5f81aca0846a6bfa64c08efa719349caca0b560787b72ea4fc3d7
Insprion/Vostro 3X8X	0.1.19.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	366d49466dc5f81aca0846a6bfa64c08efa719349caca0b560787b72ea4fc3d7
Precision 5520	0.1.30.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	5811b4bdbf93b2b7fc95200f1f246827f5f366d07d16f06b863920d0b11bf388
Precision 5520	0.1.30.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	5811b4bdbf93b2b7fc95200f1f246827f5f366d07d16f06b863920d0b11bf388
Precision 5820 Tower X-Series	0.2.22.0	Intel	Setup	899407d7-99fe-43d8-9a21-79ec328cac21	7b19487c2b25cda388d8960ea34041513b3c7726e2a0a6010f9a08969ed58a38
Inspiron 14-3467	0.2.20.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	d692fb75c9ba1779498fa6dd6f9e9463e8a590fb97dc2166f4d41d944b068085
Inspiron 14-3467	0.2.20.0	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	d692fb75c9ba1779498fa6dd6f9e9463e8a590fb97dc2166f4d41d944b068085
OptiPlex 7050	0.1.22.1	Intel	899407D7-99FE-43D8-9A21-79EC328CAC21	899407d7-99fe-43d8-9a21-79ec328cac21	d890373a028f4a868eff029342db3bd326dd23d9075c1c1101a41026ff6b8e07

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 Latitude 3300's firmware (version: 0.1.17.0, module sha256: 242a5ea5ff855aed77a41207d3f43546b13a32bb5ceab4e333e7b5f0958afb8a) as an example.

The following code in the module actually allows leaking memory:

a call to a gRT->GetVariable() offset: 0xe7cc
a call to a gRT->SetVariable() offset: 0xe9be

__int64 __fastcall sub_E790()
{
  __int64 result; // rax
  unsigned int v1; // eax
  unsigned __int64 i; // rbx
  unsigned int v3; // edx
  unsigned int v4; // ecx
  char v5; // dl
  bool v6; // cl
  int v7; // edi
  int v8; // esi
  unsigned __int64 v9; // rcx
  __int64 v10[7]; // [rsp+30h] [rbp-38h] BYREF
  int v11; // [rsp+70h] [rbp+8h] BYREF
  unsigned int v12; // [rsp+78h] [rbp+10h] BYREF
  unsigned int v13; // [rsp+80h] [rbp+18h] BYREF
  __int64 v14; // [rsp+88h] [rbp+20h] BYREF

  v10[0] = 5360i64;
  gRT->GetVariable(                             // <= first call (we can rewrite DataSize here)
    (CHAR16 *)L"CpuSetup",
    &CPU_SETUP_VARIABLE_GUID,
    (UINT32 *)&v14,
    (UINTN *)v10,
    &unk_2E570);
  result = sub_21B94(3i64, -2147483624, (char *)&v13, &v11);
  if ( !v11 )
  {
    v1 = v13;
    for ( i = 0i64; i <= 3; ++i )
    {
      if ( i )
      {
        if ( i == 1 )
        {
          v3 = v1 >> 5;
          v4 = v1 >> 9;
        }
        else if ( i == 2 )
        {
          v3 = v1 >> 15;
          v4 = v1 >> 19;
        }
        else
        {
          v3 = v1 >> 20;
          v4 = HIBYTE(v1);
        }
      }
      else
      {
        LOBYTE(v3) = v1;
        v4 = v1 >> 4;
      }
      v5 = v3 & 0xF;
      v6 = (v4 & 1) == 0;
      if ( *((_BYTE *)&unk_2E570 + i + 1438) == 1 && v6 )
      {
        v7 = v5 & 0xF;
        v8 = v7 << 16;
        sub_21B94(3i64, (v7 << 16) | 0x80000118, (char *)&v12, &v11);
        if ( !v11 )
        {
          v9 = (100000 * ((unsigned __int64)v12 >> 16) + 0x80000) >> 20;
          *((_WORD *)&unk_2E570 + i + 721) = (100000 * (unsigned __int64)(unsigned __int16)v12 + 0x80000) >> 20;
          *((_WORD *)&unk_2E570 + i + 725) = v9;
        }
        sub_21B94(3i64, v8 | 0x80000518, (char *)&v12, &v11);
        if ( !v11 )
          *((_WORD *)&unk_2E570 + i + 753) = v12;
        sub_21B94(3i64, v8 | 0x80000718, (char *)&v12, &v11);
        if ( !v11 )
          *((_WORD *)&unk_2E570 + i + 757) = (1000 * v12 + 4096) >> 13;
        sub_21B94(3i64, (v7 << 8) | 0x80000019, (char *)&v12, &v11);
        if ( !v11 )
          *((_WORD *)&unk_2E570 + i + 761) = v12 & 0x7FFF;
        v1 = v13;
      }
    }
    return gRT->SetVariable(                    // <= second call
             (CHAR16 *)L"CpuSetup",
             &CPU_SETUP_VARIABLE_GUID,
             v14,
             v10[0],
             &unk_2E570);
  }
  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 CpuSetup NVRAM variable is greater than 5360.

Thus, a potential attacker can dump X - 5360 bytes from the stack (or global memory) into CpuSetup NVRAM variable by setting CpuSetup NVRAM variable's size to X > 5360.

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

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