BRLY-2022-070

OOB write vulnerability in SMI handler leads to arbitrary code execution in SMM.

Public Disclosure Date: Jun 21, 2023

CVE ID

CVE-2023-32472

Summary

BINARLY efiXplorer team has discovered a OOB write vulnerability that allows a possible attacker to hijack execution flow of a code running in System Management Mode. Exploiting this issue could lead to escalating privileges to SMM.

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Potential Impact

An attacker can exploit this vulnerability to elevate privileges from ring 0 to ring -2, execute arbitrary code in System Management Mode - an environment more privileged than operating system (OS) and completely isolated from it. Running arbitrary code in SMM additionally bypasses SMM-based SPI flash protections against modifications, which can help an attacker to install a firmware backdoor/implant into the BIOS. Such a malicious firmware code in the BIOS could persist across operating system re-installs. Additionally, this vulnerability could potentially be used by threat actors to bypass security mechanisms provided by the UEFI firmware (for example, Secure Boot and some types of memory isolation for hypervisors).

Vulnerability Information

BINARLY internal vulnerability identifier: BRLY-2022-070
Dell PSIRT assigned CVE identifier: CVE-2023-32472
DSA identifier: DSA-2023-225/DSA-2023-225
CVSS v3.1: 7.2 High AV:P/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Table of Contents

01.Affected Dell firmware

02.Vulnerability description

03.Disclosure timeline

04.Acknowledgements

Affected Dell firmware

Product	Firmware version	CPU	Module name	Module GUID	Module SHA256
Edge Gateway 5200	105	Intel	SmbiosDmiEdit	e2a74738-8934-48f5-8412-99e948c8dc1b	ecbed907011a179b468d0923bc8fff7a3208e4d4cd2b31c080b96deb5a1b4aa9

Vulnerability description

Let's take Edge Gateway 5200's firmware (version: 105, module sha256: ecbed907011a179b468d0923bc8fff7a3208e4d4cd2b31c080b96deb5a1b4aa9) as an example.

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

a call to a gRT->GetVariable() offset: 0x147b
a call to a gRT->GetVariable() offset: 0x14a3

__int64 __fastcall sub_143C()
{
  __int64 v1; // [rsp+40h] [rbp+8h] BYREF

  v1 = 8i64;
  (gRT_0->GetVariable)(                         // <= first call (we can rewrite DataSize here)
    L"SmbiosEntryPointTable",
    &EFI_SMBIOS_NVRAM_DATA_GUID,
    0i64,
    &v1,
    &gSmbiosEntryPointTable);
  (gRT_0->GetVariable)(                         // <= second call
    L"SmbiosEntryPointTableF000",
    &EFI_SMBIOS_NVRAM_DATA_GUID,
    0i64,
    &v1,
    &gSmbiosEntryPointTableF000);
  v1 = 8i64;
  (gRT_0->GetVariable)(L"SmbiosV3EntryPointTable", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &qword_69E8);
  v1 = 8i64;
  (gRT_0->GetVariable)(L"SmbiosScratchBuffer", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &qword_69F8);
  v1 = 2i64;
  return (gRT_0->GetVariable)(L"MaximumTableSize", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &word_6B10);
}

This code is part of the SMI software handler (SwSmiHandler), which is registered as follows:

...
result = gSmst_1->SmmLocateProtocol(&EFI_SMM_SW_DISPATCH2_PROTOCOL_GUID, 0, &EfiSmmSwDispatch2Protocol);
if ( result >= 0 )
{
  RegisterContext.SwSmiInputValue = 0x50;
  result = EfiSmmSwDispatch2Protocol->Register(
              EfiSmmSwDispatch2Protocol,
              SwSmiHandler,
              &RegisterContext,
              &DispatchHandle);
  if ( result >= 0 )
  {
    RegisterContext.SwSmiInputValue = 0x51;
    result = EfiSmmSwDispatch2Protocol->Register(
                EfiSmmSwDispatch2Protocol,
                SwSmiHandler,
                &RegisterContext,
                &DispatchHandle);
    if ( result >= 0 )
    {
      RegisterContext.SwSmiInputValue = 0x52;
      result = EfiSmmSwDispatch2Protocol->Register(
                  EfiSmmSwDispatch2Protocol,
                  SwSmiHandler,
                  &RegisterContext,
                  &DispatchHandle);
      if ( result >= 0 )
      {
        RegisterContext.SwSmiInputValue = 0x53;
        v2 = (EfiSmmSwDispatch2Protocol->Register)(
                EfiSmmSwDispatch2Protocol,
                SwSmiHandler,
                &RegisterContext,
                &DispatchHandle);
        if ( v2 < 0 )
          return v2;
        return v0;
      }
    }
  }
}
...

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

If the length of SmbiosEntryPointTable NVRAM variable is greater than 8, the second call to gRT->GetVariable() service will overflow a global buffer (&gSmbiosEntryPointTableF000), which in turn could lead to arbitrary code execution.

In this case OOB write allow to rewrite SMM_RUNTIME_SERVICES vendor table address:

.data:00000000000069D8 gSmbiosEntryPointTableF000 dq ?
.data:00000000000069E0 qword_69E0      dq ?
.data:00000000000069E8 qword_69E8      dq ?
.data:00000000000069F0 qword_69F0      dq ?
.data:00000000000069F8 qword_69F8      dq ?
.data:0000000000006A00 qword_6A00      dq ?
.data:0000000000006A08 gST             dq ?
.data:0000000000006A10 gBS             dq ?
.data:0000000000006A18 ; SMM_RUNTIME_SERVICES vendor table address that attacker able to rewrite
.data:0000000000006A18 gRT             dq ?

Next call to gRT->GetVariable() will lead a code execution.

To fix this vulnerability the DataSize must be re-initialized with the size of SmbiosEntryPointTableF000 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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Potential Impact

Product

Firmware version

CPU

Module name

Module GUID

Module SHA256

Edge Gateway 5200

105

Intel

SmbiosDmiEdit

e2a74738-8934-48f5-8412-99e948c8dc1b

ecbed907011a179b468d0923bc8fff7a3208e4d4cd2b31c080b96deb5a1b4aa9

__int64 __fastcall sub_143C() { __int64 v1; // [rsp+40h] [rbp+8h] BYREF v1 = 8i64; (gRT_0->GetVariable)( // <= first call (we can rewrite DataSize here) L"SmbiosEntryPointTable", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &gSmbiosEntryPointTable); (gRT_0->GetVariable)( // <= second call L"SmbiosEntryPointTableF000", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &gSmbiosEntryPointTableF000); v1 = 8i64; (gRT_0->GetVariable)(L"SmbiosV3EntryPointTable", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &qword_69E8); v1 = 8i64; (gRT_0->GetVariable)(L"SmbiosScratchBuffer", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &qword_69F8); v1 = 2i64; return (gRT_0->GetVariable)(L"MaximumTableSize", &EFI_SMBIOS_NVRAM_DATA_GUID, 0i64, &v1, &word_6B10); }

... result = gSmst_1->SmmLocateProtocol(&EFI_SMM_SW_DISPATCH2_PROTOCOL_GUID, 0, &EfiSmmSwDispatch2Protocol); if ( result >= 0 ) { RegisterContext.SwSmiInputValue = 0x50; result = EfiSmmSwDispatch2Protocol->Register( EfiSmmSwDispatch2Protocol, SwSmiHandler, &RegisterContext, &DispatchHandle); if ( result >= 0 ) { RegisterContext.SwSmiInputValue = 0x51; result = EfiSmmSwDispatch2Protocol->Register( EfiSmmSwDispatch2Protocol, SwSmiHandler, &RegisterContext, &DispatchHandle); if ( result >= 0 ) { RegisterContext.SwSmiInputValue = 0x52; result = EfiSmmSwDispatch2Protocol->Register( EfiSmmSwDispatch2Protocol, SwSmiHandler, &RegisterContext, &DispatchHandle); if ( result >= 0 ) { RegisterContext.SwSmiInputValue = 0x53; v2 = (EfiSmmSwDispatch2Protocol->Register)( EfiSmmSwDispatch2Protocol, SwSmiHandler, &RegisterContext, &DispatchHandle); if ( v2 < 0 ) return v2; return v0; } } } } ...

.data:00000000000069D8 gSmbiosEntryPointTableF000 dq ? .data:00000000000069E0 qword_69E0 dq ? .data:00000000000069E8 qword_69E8 dq ? .data:00000000000069F0 qword_69F0 dq ? .data:00000000000069F8 qword_69F8 dq ? .data:0000000000006A00 qword_6A00 dq ? .data:0000000000006A08 gST dq ? .data:0000000000006A10 gBS dq ? .data:0000000000006A18 ; SMM_RUNTIME_SERVICES vendor table address that attacker able to rewrite .data:0000000000006A18 gRT dq ?

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

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Potential Impact

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Vulnerability Information

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Affected Dell firmware

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Vulnerability description

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Disclosure timeline

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Acknowledgements

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Get started today, Ship and Buy Software You Can Prove Is Safe

Potential Impact

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Vulnerability Information

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Affected Dell firmware

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Vulnerability description

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Disclosure timeline

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Acknowledgements

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Get started today, Ship and Buy Software You Can Prove Is Safe