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