[BRLY-2022-145] 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-2022-145
Dell PSIRT assigned CVE identifier: CVE-2023-28026
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
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
Inspiron 3910-China HDD Protection	0.1.7.3	Intel	Setup	e6a7a1ce-5881-4b49-80be-69c91811685c	dccccb8c891fdfb772ce9ed8130b65897bff4ab6bc0f2e91055d169f528df4d1
Latitude 3301	0.1.17.0	Intel	Setup	e6a7a1ce-5881-4b49-80be-69c91811685c	e4f86398668c72865f121e2ff10136da190c9fc18b4835ff0426d8ccb504cb25

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 Inspiron 15 3511, Vostro 15 3510's firmware (version: 0.1.18.2, module sha256: 85d1e1cf6f5175d22ab262bc5034720287bfaf54e5a1b9074e624b106f627808) as an example.

The following code in the module actually allows leaking memory:

a call to a gRT->GetVariable() offset: 0xd15
a call to a gRT->SetVariable() offset: 0xd41

__int64 __fastcall sub_BC8(EFI_CAPSULE_HEADER **a1)
{
  __int64 result; // rax
  __int64 v3; // [rsp+30h] [rbp-D0h] BYREF
  _BYTE v4[144]; // [rsp+40h] [rbp-C0h] BYREF
  _BYTE v5[688]; // [rsp+D0h] [rbp-30h] BYREF
  _BYTE v6[1072]; // [rsp+380h] [rbp+280h] BYREF
  _BYTE v7[1952]; // [rsp+7B0h] [rbp+6B0h] BYREF
  _BYTE v8[2096]; // [rsp+F50h] [rbp+E50h] BYREF
  __int64 v9; // [rsp+17A0h] [rbp+16A0h] BYREF
  __int64 v10; // [rsp+17A8h] [rbp+16A8h] BYREF

  result = ((__int64 (__fastcall *)(EFI_GUID *, _QWORD, __int64 *))gBS->LocateProtocol)(
             &AMI_TSE_SETUP_ENTER_PROTOCOL_GUID,
             0i64,
             &v3);
  if ( result >= 0 )
  {
    sub_11D84();
    v10 = 1943i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"Setup",
      &EFI_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      v7);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(// <= second call
      L"ColdReset",
      &EFI_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      v7);
    v10 = 1057i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"SaSetup",
      &SA_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      v6);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(// <= second call
      L"SaColdReset",
      &SA_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      v6);
    v10 = 143i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"MeSetup",
      &ME_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      v4);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(// <= second call
      L"MeColdReset",
      &ME_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      v4);
    v10 = 678i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"CpuSetup",
      &CPU_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      v5);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(// <= second call
      L"CpuColdReset",
      &CPU_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      v5);
    v10 = 2083i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"PchSetup",
      &PCH_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      v8);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(// <= second call
      L"PchColdReset",
      &PCH_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      v8);
    v10 = 2i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, __int64 *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"SiSetup",
      &SI_SETUP_VARIABLE_GUID,
      0i64,
      &v10,
      &v9);
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, __int64 *))gRT->SetVariable)(// <= second call
      L"SiColdReset",
      &SI_SETUP_VARIABLE_GUID,
      2i64,
      v10,
      &v9);
    return ((__int64 (__fastcall *)(EFI_CAPSULE_HEADER **))gBS->CloseEvent)(a1);
  }
  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 MeSetup NVRAM variable is greater than 143.

Thus, a potential attacker can dump X - 143 bytes from the stack (or global memory) into MeColdReset NVRAM variable by setting MeSetup NVRAM variable's size to X > 143.

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