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Advisory ID:
BRLY-2022-054

[BRLY-2022-054] Stack buffer overflow vulnerability leads to arbitrary code execution in DXE driver on multiple Dell platforms.

June 22, 2023
Severity:
High
CVSS Score
8.2
Public Disclosure Date:
June 21, 2023
CVE ID:
CVE-2023-28036

Summary

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

Vendors Affected

Affected Products

Latitude 9520
,

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.

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-2022-054
  • Dell PSIRT assigned CVE identifier: CVE-2023-28036
  • DSA identifier: DSA-2023-099/DSA-2023-204
  • 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

Product Firmware version CPU Module name Module GUID Module SHA256
Latitude 9520 0.1.17.0 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c 3d3150a82da8f1e143f85bfe50d894a735886c243b3dd93209b1346ad200c054
Inspiron 15 3511, Vostro 15 3510 0.1.18.2 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c 85d1e1cf6f5175d22ab262bc5034720287bfaf54e5a1b9074e624b106f627808
XPS 13 9365 0.2.24.0 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c befd809dc391328ad5553f72f6528c74c152fb51aef52738f2c7f5e10dcda3c4
Latitude 3301 0.1.17.0 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c e4f86398668c72865f121e2ff10136da190c9fc18b4835ff0426d8ccb504cb25
OptiPlex 3000 Thin Client 0.1.4.0 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c eec811ee26817bbc8ead55742bb2a2b9c1cb1c87814a59646660203910ccfe2a
Latitude 5420 0.1.22.0 Intel Setup e6a7a1ce-5881-4b49-80be-69c91811685c fd097b2327a983291c443da05b5f588491de06a3aa212c98a5f4bb8046241784

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 Latitude 9520's firmware (version: 0.1.17.0, module sha256: 3d3150a82da8f1e143f85bfe50d894a735886c243b3dd93209b1346ad200c054) as an example.

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

  • a call to a gRT->GetVariable() offset: 0xb2ad
  • a call to a gRT->GetVariable() offset: 0xb2d5
char sub_B220()
{
  __int64 v0; // rbx
  char result; // al
  char v2; // dl
  unsigned __int8 v3; // bl
  char v4; // dl
  int v5; // ecx
  int v6; // edx
  int v7; // ecx
  unsigned __int8 v8; // bl
  char v9; // dl
  void *Interface; // [rsp+30h] [rbp-40h] BYREF
  __int64 Data; // [rsp+38h] [rbp-38h] BYREF
  __int64 v12; // [rsp+40h] [rbp-30h]
  char v13[8]; // [rsp+48h] [rbp-28h]
  __int64 v14; // [rsp+50h] [rbp-20h] BYREF
  __int64 v15; // [rsp+58h] [rbp-18h]
  char v16; // [rsp+60h] [rbp-10h]
  int v17; // [rsp+90h] [rbp+20h] BYREF
  UINTN DataSize; // [rsp+98h] [rbp+28h] BYREF
  int v19; // [rsp+A0h] [rbp+30h] BYREF
  __int16 v20; // [rsp+A4h] [rbp+34h]
  char v21; // [rsp+A6h] [rbp+36h]
  void *HeciProtocol; // [rsp+A8h] [rbp+38h] BYREF

  Data = 0i64;
  v12 = 0i64;
  v13[0] = 0;
  v14 = 0i64;
  v15 = 0i64;
  v16 = 0;
  v19 = 0;
  v20 = 0;
  v21 = 0;
  v0 = gBS->LocateProtocol(&HECI_PROTOCOL_GUID, 0i64, &Interface);
  result = sub_FF2C();
  if ( !result && v0 >= 0 )
  {
    DataSize = 17i64;
    gRT->GetVariable(                           // <= first call (we can rewrite DataSize here)
      L"MeSetupStorage",
      &ME_SETUP_VARIABLE_GUID,
      0i64,
      &DataSize,
      &Data);
    gRT->GetVariable(                           // <= second call
      L"MeBackupStorage",
      &ME_SETUP_VARIABLE_GUID,
      0i64,
      &DataSize,
      &v14);
    DataSize = 143i64;
    gRT->GetVariable(L"MeSetup", &ME_SETUP_VARIABLE_GUID, 0i64, &DataSize, &unk_A0F80);
    DataSize = 7i64;
    gRT->GetVariable(L"TcgSetup", &EFI_SETUP_VARIABLE_GUID, 0i64, &DataSize, &v19);
    if ( BYTE4(v12) != BYTE4(v15) && !byte_A0FAA && BYTE4(v12) == 1 )
      sub_F120();
    if ( BYTE2(Data) != BYTE2(v14) )
    {
      byte_A0891 = 1;
      if ( BYTE2(Data) )
      {
        sub_F320();
      }
      else if ( (gBS->LocateProtocol(&HECI_PROTOCOL_GUID, 0i64, &HeciProtocol) & 0x8000000000000000ui64) == 0i64 )
      {
        (*(HeciProtocol + 8))(&v17);
        if ( v17 != 3 && !sub_FF2C() )
          sub_ED6C(6, v2, 0);
      }
    }
    v3 = BYTE1(Data);
    if ( BYTE1(Data) != BYTE1(v14) && !sub_FF2C() )
      sub_ED6C(7, v4, v3);
    if ( Data != v14 )
    {
      byte_A0891 = 1;
      if ( Data == 1 )
      {
        v5 = 4;
        v6 = 0;
      }
      else
      {
        v5 = 0;
        v6 = 4;
      }
      sub_F414(v5, v6);
    }
    v7 = byte_A0891;
    v8 = BYTE6(Data);
    if ( BYTE5(Data) != BYTE5(v14) )
      v7 = 1;
    byte_A0891 = v7;
    if ( BYTE6(Data) != BYTE6(v14) && v19 == 1 && !sub_FF2C() )
      sub_ED6C(47, v9, v8);
    LOBYTE(v7) = BYTE2(v12);
    if ( BYTE2(v12) != BYTE2(v15) )
    {
      byte_A0891 = 1;
      sub_EF84(SBYTE2(v12));
    }
    if ( BYTE3(v12) != BYTE3(v15) )
      sub_F5C0(BYTE3(v12));
    if ( HIBYTE(v12) != HIBYTE(v15) )
      sub_FBAC(v7, SHIBYTE(v12));
    if ( v13[0] != v16 )
      sub_FD30(v7, v13[0]);
    return gRT->SetVariable(L"MeBackupStorage", &ME_SETUP_VARIABLE_GUID, 2u, 0x11ui64, &Data);
  }
  return result;
}

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

If the length of MeSetupStorage NVRAM variable is greater than 17, 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 MeBackupStorage 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.

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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