[BRLY-2022-001] Stack buffer overflow vulnerability leads to arbitrary code execution in a DXE driver on Intel platform.

Summary

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

Vulnerability Information

• BINARLY internal vulnerability identifier: BRLY-2022-001
• Intel PSIRT assigned CVE identifier: CVE-2022-32569
• FwHunt rule: BRLY-2022-001
• CVSS v3.1: 7.5 High AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

Affected Intel firmware confirmed to be impacted by Binarly team

Potential impact

An attacker with local privileged 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

The vulnerability exists in the notifier for AMI_SETUP_NVRAM_UPDATE located at offset 0x14D48.The pseudocode for this notifier is shown below:

char __fastcall AmiSetupNvramUpdateCallback(EFI_CAPSULE_HEADER **CapsuleHeaderArray)
{
  __int64 Status; // rax
  __int64 Status_1; // rbx
  UINTN v4; // rdx
  void **v5; // r8
  char v6; // dl
  unsigned __int8 v7; // bl
  char v8; // dl
  int v9; // ecx
  int v10; // edx
  EFI_MEMORY_TYPE MemoryType; // ecx
  UINTN v12; // rdx
  EFI_PHYSICAL_ADDRESS v13; // r8
  void *v15; // [rsp+30h] [rbp-50h] BYREF
  void *Interface; // [rsp+38h] [rbp-48h] BYREF
  void *v17; // [rsp+40h] [rbp-40h] BYREF
  char MeSetupStorageData[17]; // [rsp+48h] [rbp-38h] BYREF
  char MeBackupStorageData[17]; // [rsp+60h] [rbp-20h] BYREF
  EFI_MEMORY_TYPE PoolType; // [rsp+B0h] [rbp+30h] BYREF
  UINTN DataSize; // [rsp+B8h] [rbp+38h] BYREF

  memset(MeSetupStorageData, 0, sizeof(MeSetupStorageData));
  memset(MeBackupStorageData, 0, sizeof(MeBackupStorageData));
  Status = gBS->LocateProtocol(&AMI_SETUP_NVRAM_UPDATE_GUID, 0, &Interface);
  if ( Status >= 0 )
  {
    Status_1 = gBS->LocateProtocol(&ProprietaryProtocol_2, 0, &v17);
    LOBYTE(Status) = sub_1D8C4();
    if ( !Status && Status_1 >= 0 )
    {
      DataSize = 17;
      gRT->GetVariable(L"MeSetupStorage", &gVariableGuid, 0, &DataSize, MeSetupStorageData);
      gRT->GetVariable(L"MeBackupStorage", &gVariableGuid, 0, &DataSize, MeBackupStorageData);
      DataSize = 53;
      gRT->GetVariable(L"MeSetup", &gVariableGuid, 0, &DataSize, &unk_27E60);
      if ( MeSetupStorageData[12] != MeBackupStorageData[12] && !byte_27E8A && MeSetupStorageData[12] == 1 )
        sub_1CAB8();
      if ( MeSetupStorageData[2] != MeBackupStorageData[2] )
      {
        gMemoryType = 1;
        if ( MeSetupStorageData[2] )
        {
          sub_1CCB8();
        }
        else if ( (gBS->LocateProtocol(&ProprietaryProtocol_2, 0, &v15) & 0x8000000000000000) == 0 )
        {
          (*(v15 + 8))(&PoolType, v4, v5);
          if ( PoolType != EfiBootServicesCode && !sub_1D8C4() )
            sub_1C704(6, v6, 0);
        }
      }
      v7 = MeSetupStorageData[1];
      if ( MeSetupStorageData[1] != MeBackupStorageData[1] && !sub_1D8C4() )
        sub_1C704(7, v8, v7);
      if ( MeSetupStorageData[0] != MeBackupStorageData[0] )
      {
        gMemoryType = 1;
        if ( MeSetupStorageData[0] == 1 )
        {
          v9 = 4;
          v10 = 0;
        }
        else
        {
          v9 = 0;
          v10 = 4;
        }
        sub_1CDAC(v9, v10);
      }
      MemoryType = gMemoryType;
      if ( MeSetupStorageData[5] != MeBackupStorageData[5] )
        MemoryType = EfiLoaderCode;
      gMemoryType = MemoryType;
      LOBYTE(MemoryType) = MeSetupStorageData[10];
      if ( MeSetupStorageData[10] != MeBackupStorageData[10] )
      {
        gMemoryType = 1;
        sub_1C91C(MeSetupStorageData[10]);
      }
      if ( MeSetupStorageData[11] != MeBackupStorageData[11] )
        sub_1CF58(MeSetupStorageData[11]);
      if ( MeSetupStorageData[15] != MeBackupStorageData[15] )
        sub_1D544(MemoryType, MeSetupStorageData[15]);
      if ( MeSetupStorageData[16] != MeBackupStorageData[16] )
        sub_1D6C8(MemoryType, MeSetupStorageData[16]);
      LOBYTE(Status) = gRT->SetVariable(L"MeBackupStorage", &gVariableGuid, 2, 0x11, MeSetupStorageData);
      if ( CapsuleHeaderArray )
        LOBYTE(Status) = (gBS->CloseEvent)(CapsuleHeaderArray, v12, v13);
    }
  }
  return Status;
}

Consider the following code snippet:

DataSize = 17;
gRT->GetVariable(L"MeSetupStorage", &gVariableGuid, 0, &DataSize, MeSetupStorageData);
gRT->GetVariable(L"MeBackupStorage", &gVariableGuid, 0, &DataSize, MeBackupStorageData);

An attacker can change the values of the MeSetupStorage and MeBackupStorage variables.If the size of the value of the MeSetupStorageData variable is greater than 17, then after the first call to the GetVariable service, the DataSize variable will be overwritten (this means that the attacker is in control of the DataSize variable).The second call to GetVariable (for the MeBackupStorage variable) can lead to a stack overflow and arbitrary code execution.

Disclosure timeline

This vulnerability is subject to a 90 day disclosure deadline. After 90 days elapsed or a patch has been made broadly available (whichever is earlier), the vulnerability report will become visible to the public.

Acknowledgements

BINARLY efiXplorer team