SMM memory corruption vulnerability in SMM module on Dell device (SMRAM write).
BINARLY REsearch team has discovered a SMM memory corruption vulnerability in a Dell device allowing a possible attacker to write fixed or predictable data to SMRAM. 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 BIOS. Such a malicious firmware code in BIOS could persist across operating system re-installs. Additionally, this vulnerability potentially could be used by malicious actors to bypass security mechanisms provided by UEFI firmware (for example, Secure Boot and some types of memory isolation for hypervisors).
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Vulnerability Information
- BINARLY internal vulnerability identifier: BRLY-DVA-2024-023
- Dell PSIRT assigned CVE identifier: CVE-2024-32858/CVE-2024-32859
- DSA identifier: DSA-2024-124
- CVSS v3.1: 8.2 High AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
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Affected Dell firmware
| Device name | Unpacked firmware SHA256 | Firmware version | IBV | Module name | Module GUID | Module SHA256 | Module kind |
|---|---|---|---|---|---|---|---|
Alienware 13 R2 | e6819bd24e063807336994f36e1b7cafbbec46c2679a365dde1b54b720a049e4 | 1.13.1 | AMI | OememSmiBin | 0a602c5b-05a0-40c4-9181-edcd891d0002 | 958a22e203308d5994047adf1e43638a59f337b4cdf34b007326a2b0f5f1569e | SmmModule |
Alienware 15 R2 and 17 R3 | 003130dabf11c8b5df286d9584b3174faa9529cd6149513d13c7ce85d63d97b0 | 1.13.1 | AMI | OememSmiBin | 0a602c5b-05a0-40c4-9181-edcd891d0002 | c20688cba3c5e6b56cd374285e6c0a1dd07cc614e48b005ec6582a3c28cafa7f | SmmModule |
Inspiron 15 7557 | 4f29eb1cc76a1413fcbce0c4a97a4fc1e234d1eab62789271be95b411cf77f01 | 1.2.3 | AMI | OememSmiBin | 0a602c5b-05a0-40c4-9181-edcd891d0002 | 7e91e198cd8f016bc54703ba62edb0f50974a1f34ab01824f72908c3890c03f1 | SmmModule |
For supported affected platforms, Dell has addressed this vulnerability in DSA-2024-124. All other affected platforms have been determined to be End of Support Life.
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Vulnerability description
Let's consider the vulnerability on the example of a module with SHA256 c20688cba3c5e6b56cd374285e6c0a1dd07cc614e48b005ec6582a3c28cafa7f.
The pseudocode of the vulnerable function is presented below:
__int64 __fastcall SwSmiHandler(
EFI_HANDLE DispatchHandle,
const void *Context,
UINTN *CommBuffer,
UINTN *CommBufferSize)
{
UINTN Index; // r9
__int64 v5; // rbx
_DWORD *ControllablePtr; // rdi
_DWORD *Ptr; // r11
__int16 v8; // ax
__int64 v9; // rcx
EFI_GUID VendorGuid; // [rsp+30h] [rbp-228h] BYREF
UINTN DataSize; // [rsp+40h] [rbp-218h] BYREF
unsigned int RbxValue; // [rsp+22Ch] [rbp-2Ch] BYREF
_DWORD *DellGnvsPtr; // [rsp+270h] [rbp+18h] BYREF
Index = *CommBuffer;
v5 = 0;
VendorGuid.Data2 = 0x5A0;
VendorGuid.Data3 = 0x40C4;
VendorGuid.Data1 = 0xA602C5B;
VendorGuid.Data4[0] = 0x91;
VendorGuid.Data4[1] = 0x81;
VendorGuid.Data4[2] = 0xED;
VendorGuid.Data4[3] = 0xCD;
VendorGuid.Data4[4] = 0x89;
VendorGuid.Data4[5] = 0x1D;
VendorGuid.Data4[6] = 0;
VendorGuid.Data4[7] = 3;
gEfiSmmCpuProtocol->ReadSaveState(gEfiSmmCpuProtocol, 4, EFI_SMM_SAVE_STATE_REGISTER_RBX, Index, &RbxValue);
ControllablePtr = RbxValue;
DataSize = 4;
gRT_0->GetVariable(L"DELL_GNVS_PTR", &VendorGuid, 0, &DataSize, &DellGnvsPtr);
Ptr = DellGnvsPtr;
if ( *DellGnvsPtr == 'TESQ' )
{
ControllablePtr = DellGnvsPtr + 2;
*DellGnvsPtr = 0; // unchecked write (SMRAM corruption)
Ptr = DellGnvsPtr;
}
if ( *Ptr == 'DESQ' )
{
ControllablePtr = Ptr + 2;
*Ptr = 0; // unchecked write (SMRAM corruption)
}
v8 = *gFuncTable;
if ( *gFuncTable != 255 )
{
v9 = 0;
while ( v8 != *ControllablePtr || *&gFuncTable[v9 + 2] != *(ControllablePtr + 1) )
{
++v5;
v9 = 12 * v5;
v8 = *&gFuncTable[12 * v5];
if ( v8 == 255 )
return 0;
}
// multiple unchecked writes (SMRAM corruption) in functions from gFuncTable
(*&gFuncTable[12 * v5 + 4])(ControllablePtr);
}
return 0;
}
The GetVariable call initializes DellGnvsPtr with the value stored in the DELL_GNVS_PTR NVRAM variable.
Since the DELL_GNVS_PTR NVRAM variable is controlled by an attacker, they can perform an arbitrary write operation here:
*DellGnvsPtr = 0; // unchecked write (SMRAM corruption)
...
*Ptr = 0; // unchecked write (SMRAM corruption)
It must be noted that these write can be reached only if DellGnvsPtr points to the signatures DESQ or TESQ, thus limiting the memory locations that can be corrupted by an attacker. However, an attacker can overwrite these signatures during the first run of the SMI handler (by pointing to the code with signatures), then obtain a more powerful write primitive in one of the functions from the gFuncTable. For example in the first function from the gFuncTable:
char __fastcall sub_6A9C(__int64 Ptr)
{
// [COLLAPSED LOCAL DECLARATIONS. PRESS NUMPAD "+" TO EXPAND]
v2 = *(Ptr + 4);
v3 = *(Ptr + 2) == 1;
DataSize = 3072;
v4 = 14;
if ( v3 )
v4 = 0;
if ( *(Ptr + 2) == 2 )
v4 = 0;
if ( v2 < v4 )
{
// ...
// SMRAM write
*(Ptr + 24) = v10 >> v8;
*(Ptr + 28) = *(&off_D50 + v6 + 24);
LODWORD(v5) = *(&off_D50 + v6 + 28);
*(Ptr + 20) = 0;
*(Ptr + 32) = v5;
}
else
{
LOBYTE(v5) = sub_5DC8(Ptr);
if ( !v5 )
LABEL_7:
*(Ptr + 20) = -1; // SMRAM write
}
return v5;
}
In order to fix this vulnerability, all user-controllable offsets and pointers should be checked with SmmIsBufferOutsideSmmValid() or analogues before any write attempt.
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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 |
|---|---|
Dell PSIRT is notified | 2024-06-18 |
Dell PSIRT is confirmed issue | 2024-08-21 |
BINARLY public disclosure date | 2025-04-04 |
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Acknowledgements
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