SMM memory corruption vulnerability in SMM module on Gigabyte device (SMRAM write)

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-2025-009
• CERT/CC assigned CVE identifier: CVE-2025-7027
• CVSS v3.1: 8.2 High AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

Affected firmware with confirmed impact by BINARLY team

Vulnerability description

Let's consider the module 5f42fc844985adaf4dcb21aeced55f40128e33ef454607f910cbedf7e9e08c4a.

The pseudocode of the vulnerable function at 0x179B8 is shown below (SwSmiInputValue: 0xB2):

EFI_STATUS SwSmiHandler(
        EFI_HANDLE DispatchHandle,
        const void *Context,
        EFI_SMM_SW_CONTEXT *CommBuffer,
        UINTN *CommBufferSize)
{
  UINTN SwSmiCpuIndex;
  INT32 Result;
  UINT32 RbxRegister;
  UINT32 RcxRegister;
  UINT32 Value;

  Value = 0;
  if ( CommBuffer && CommBufferSize )
    SwSmiCpuIndex = CommBuffer->SwSmiCpuIndex;
  else
    SwSmiCpuIndex = Value;
  if ( SwSmiCpuIndex != -1 )
  {
    // 1. read buffer address in RbxRegister
    gEfiSmmCpuProtocol->ReadSaveState(
      gEfiSmmCpuProtocol,
      4,
      EFI_SMM_SAVE_STATE_REGISTER_RBX,
      SwSmiCpuIndex,
      &RbxRegister);

    // 2. read command in RcxRegister
    gEfiSmmCpuProtocol->ReadSaveState(
      gEfiSmmCpuProtocol,
      4,
      EFI_SMM_SAVE_STATE_REGISTER_RCX,
      SwSmiCpuIndex,
      &RcxRegister);

    if ( RcxRegister )
    {
      if ( RcxRegister != 1 )
      {
        Value = 0x8004;
_WriteRbx:
        gEfiSmmCpuProtocol->WriteSaveState(
          gEfiSmmCpuProtocol,
          4,
          EFI_SMM_SAVE_STATE_REGISTER_RBX,
          SwSmiCpuIndex,
          &Value);
        return 0;
      }
      // vulnerable function
      Result = CommandRcx1(RbxRegister);
    }
    else
    {
      Result = CommandRcx0(RbxRegister);
    }
    Value = Result;
    if ( (Result - 0x9001) <= 1 )
    {
      gEfiSmmCpuProtocol->WriteSaveState(
        gEfiSmmCpuProtocol,
        4,
        EFI_SMM_SAVE_STATE_REGISTER_RCX,
        SwSmiCpuIndex,
        &Value);
      Value = 0xFFFF;
    }
    goto _WriteRbx;
  }
  return 0;
}

As we can see from the pseudocode, this handler defines the following logic:

• read command from EFI_SMM_SAVE_STATE_REGISTER_RCX in RcxRegister variable
• read buffer address from EFI_SMM_SAVE_STATE_REGISTER_RBX in RbxRegister variable
• execute CommandRcx1 or CommandRcx0 depending on RcxRegister (command) value

The pseudocode of the CommandRcx1 function is shown below:

INT32 CommandRcx1(BIOS_SETTINGS_DATA_HEADER *RbxRegister)
{
  if ( RbxRegister->Signature != '2DB$' )
    return 0x8001;
  GetSetupXtuBufferAddress(&SetupXtuBufferAddress);
  ControlledPtrFromVariable = SetupXtuBufferAddress;
  ControlledPtrFromSaveState = RbxRegister + 1;
  if ( RbxRegister->Count )
  {
    Count = RbxRegister->Count;
    do
    {
      Sig = ControlledPtrFromSaveState->Signature;
      if ( (LOBYTE(ControlledPtrFromSaveState->Signature) - 7) > 7 )
      {
        if ( Sig == 15 )
        {
          Res = 7;
        }
        else if ( (Sig - 0x1A) > 9 )
        {
          Val = ControlledPtrFromSaveState->Signature;
          if ( Sig == 0x19 )
            Val = '#';
          Res = Val;
        }
        else
        {
          Res = Sig - 1;
        }
      }
      else
      {
        Res = Sig + 1;
      }
      Length = ControlledPtrFromSaveState->Length;
      ControlledPtrFromSaveState = (ControlledPtrFromSaveState + 8);
      // SMRAM write and limited SMRAM read,
      // SetupXtuBufferAddress and ControlledPtrFromSaveState are not validated
      *(ControlledPtrFromVariable + 2 * Res + 0xC) = Length;
      --Count;
    }
    while ( Count );
  }
  ...
}

EFI_STATUS GetSetupXtuBufferAddress(UINT64 *SetupXtuBufferAddressOut)
{
  UINT64 SetupXtuBufferAddress;
  UINTN DataSize;

  SetupXtuBufferAddress = 0;
  DataSize = 8;
  gRT->GetVariable(L"SetupXtuBufferAddress", &gVendorGuid, 0, &DataSize, &SetupXtuBufferAddress);
  *SetupXtuBufferAddressOut = SetupXtuBufferAddress;
  return 0;
}

As we can see from the pseudo code:

• ControlledPtrFromVariable - address obtained from SetupXtuBufferAddress NVRAM variable value
• ControlledPtrFromSaveState - address obtained from attacker controlled RbxRegister value

The following code allows an attacker to write controllable data to a controllable address inside SMRAM:

Length = ControlledPtrFromSaveState->Length;
ControlledPtrFromSaveState = (ControlledPtrFromSaveState + 8);
// SMRAM write and limited SMRAM read,
// SetupXtuBufferAddress and ControlledPtrFromSaveState are not validated
*(ControlledPtrFromVariable + 2 * Res + 0xC) = Length;

Disclosure timeline

This vulnerability is subject to a 90 day disclosure period. After 90 days or when a patch has been made generally available (whichever comes first) the advisory will be publicly disclosed.

Acknowledgements

BINARLY REsearch team