[BRLY-2022-169] 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-2022-169
• Dell PSIRT assigned CVE identifier: CVE-2023-25936
• 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

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: e0c5654ae009fe58b2a6ab2d68c9ee3a37c65e81e5c5f7fa3236ee5dacccef97) as an example.

The following code in the module actually allows leaking memory:

• a call to a gRT->GetVariable() offset: 0x58c
• a call to a gRT->SetVariable() offset: 0x605

__int64 __fastcall sub_42C()
{
  __int64 result; // rax
  void (__fastcall *v1)(int); // rax
  __int64 v2; // rbx
  int v3; // [rsp+30h] [rbp-2128h] BYREF
  __int16 v4; // [rsp+34h] [rbp-2124h]
  __int16 v5; // [rsp+36h] [rbp-2122h]
  char v6; // [rsp+38h] [rbp-2120h]
  char v7; // [rsp+39h] [rbp-211Fh]
  char v8; // [rsp+3Ah] [rbp-211Eh]
  char v9; // [rsp+3Bh] [rbp-211Dh]
  char v10; // [rsp+3Ch] [rbp-211Ch]
  char v11; // [rsp+3Dh] [rbp-211Bh]
  char v12; // [rsp+3Eh] [rbp-211Ah]
  char v13; // [rsp+3Fh] [rbp-2119h]
  int v14; // [rsp+40h] [rbp-2118h] BYREF
  __int16 v15; // [rsp+44h] [rbp-2114h]
  __int16 v16; // [rsp+46h] [rbp-2112h]
  char v17; // [rsp+48h] [rbp-2110h]
  char v18; // [rsp+49h] [rbp-210Fh]
  char v19; // [rsp+4Ah] [rbp-210Eh]
  char v20; // [rsp+4Bh] [rbp-210Dh]
  char v21; // [rsp+4Ch] [rbp-210Ch]
  char v22; // [rsp+4Dh] [rbp-210Bh]
  char v23; // [rsp+4Eh] [rbp-210Ah]
  char v24; // [rsp+4Fh] [rbp-2109h]
  __int64 v25; // [rsp+50h] [rbp-2108h] BYREF
  _QWORD v26[3]; // [rsp+58h] [rbp-2100h] BYREF
  _BYTE v27[128]; // [rsp+70h] [rbp-20E8h] BYREF
  __int64 v28; // [rsp+F0h] [rbp-2068h] BYREF
  char v29; // [rsp+13Dh] [rbp-201Bh]
  _BYTE v30[4024]; // [rsp+800h] [rbp-1958h] BYREF
  char v31; // [rsp+17B8h] [rbp-9A0h]
  unsigned int v32; // [rsp+2160h] [rbp+8h] BYREF
  unsigned int v33; // [rsp+2168h] [rbp+10h] BYREF
  __int64 v34; // [rsp+2170h] [rbp+18h] BYREF
  __int64 v35; // [rsp+2178h] [rbp+20h] BYREF

  v14 = -2124212326;
  v15 = -3302;
  v17 = -82;
  v16 = 16690;
  v18 = -34;
  v4 = -5212;
  v19 = -119;
  v20 = -13;
  v21 = 106;
  v22 = -18;
  v5 = 19381;
  v23 = 67;
  v24 = -38;
  v35 = 6475i64;
  v25 = 114i64;
  v26[0] = 1805i64;
  v3 = -326642109;
  v6 = -95;
  v7 = -27;
  v8 = 63;
  v9 = 62;
  v10 = 54;
  v11 = -78;
  v12 = 13;
  v13 = -87;
  sub_2970(qword_3688);
  (gRT_0->GetVariable)(L"Setup", &v3, &v34, v26, &v28);
  result = (gRT_0->GetVariable)(L"SocketIioConfig", &EFI_SOCKET_IIO_VARIABLE_GUID, &v32, &v35, v30);
  if ( v29 != v31 )
  {
    (gRT_0->GetVariable)(                       // <= first call (we can rewrite DataSize here)
      L"SocketCommonRcConfig",
      &EFI_SOCKET_COMMON_RC_VARIABLE_GUID,
      &v33,
      &v25,
      v27);
    v31 = v29;
    v27[6] = 3;
    (gRT_0->SetVariable)(L"SocketIioConfig", &EFI_SOCKET_IIO_VARIABLE_GUID, v32, v35, v30);
    (gRT_0->SetVariable)(                       // <= second call
      L"SocketCommonRcConfig",
      &EFI_SOCKET_COMMON_RC_VARIABLE_GUID,
      v33,
      v25,
      v27);
    (gRT_0->SetVariable)(L"LastBootFailedIoh", &v14, 3i64);
    v1 = funcs_636[0];
    v2 = 0i64;
    while ( v1 )
    {
      v1(0);
      v1 = funcs_636[++v2];
    }
    sub_28D4(0i64, 31i64, 2);
    __outbyte(0xCF9u, 2u);
    __outbyte(0xCF9u, 6u);
    v26[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 SocketCommonRcConfig NVRAM variable is greater than 114.

Thus, a potential attacker can dump X - 114 bytes from the stack (or global memory) into SocketCommonRcConfig NVRAM variable by setting SocketCommonRcConfig NVRAM variable's size to X > 114.

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