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-2024-012
- 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 |
|---|---|---|---|---|---|---|---|
Inspiron 15 5576 Gaming | 80fd3fc96653acfcad13dee7feb0b663140791ded24c18bcdcd329adf5ae980e | 1.0.7 | AMI | DellDiagSmm | 6983d90e-3ef7-4d09-8f36-63ae0c59cff2 | 6d8cce3c22200ce2a249eb99ae523e078fb7dc829d778c473434b871ed5becce | SmmModule |
Inspiron 15 5577 Gaming | 857e55f7f0f052ad129dd12e971f63afe015123757d6e8508b2f0cb20bdc5a3e | 1.1.3 | AMI | DellDiagSmm | 6983d90e-3ef7-4d09-8f36-63ae0c59cff2 | 7960b155e87a49d9be867a0eec9ce9beeb1a99a0501ead408619cb9a143e7e3a | SmmModule |
Inspiron 15 7559 | f048d8e235bd2b03f888882e4ec831caf8ea70d4cc9ebb9606f6cae63dc49d7a | 1.3.1 | AMI | DellDiagSmm | 6983d90e-3ef7-4d09-8f36-63ae0c59cff2 | a4dd1f58f6e856d1528c08d98516e40594fbdc71fd6b4d40a1e074f686779a58 | SmmModule |
Vostro 14 5459 | 58ad1c2a1cc09823b57ca1e976fa2ef24d1a4572f187f589f9d51cc09c18992d | 1.1.7 | AMI | DellDiagSmm | 6983d90e-3ef7-4d09-8f36-63ae0c59cff2 | cdb48f86112ff4b6b8cda61212a19a606cc88f52b91fd799755e1133e1296505 | SmmModule |
For supported affected platforms, Dell has addressed this vulnerability in DSA-2024-124. All reported 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 cdb48f86112ff4b6b8cda61212a19a606cc88f52b91fd799755e1133e1296505.
The pseudocode of the vulnerable function is presented below:
unsigned __int8 __fastcall sub_742C(_DWORD *a1)
{
// [COLLAPSED LOCAL DECLARATIONS. PRESS NUMPAD "+" TO EXPAND]
Guid.Data2 = 0x5A0;
Guid.Data1 = 0xA602C5B;
Guid.Data4[0] = 0x91;
Guid.Data4[1] = 0x81;
Guid.Data4[2] = 0xED;
Guid.Data3 = 0x40C4;
Guid.Data4[3] = 0xCD;
Guid.Data4[4] = 0x89;
Guid.Data4[5] = 0x1D;
Guid.Data4[6] = 0;
Guid.Data4[7] = 3;
if ( !gDellGnvsPtr )
{
DataSize = 4;
gRT_0->GetVariable(L"DELL_GNVS_PTR", &Guid, 0, &DataSize, &gDellGnvsPtr);
}
a1[6] = 0;
a1[8] = 0;
sub_5F58();
__outbyte(0x380, 0x83);
v3 = 897LL;
v4 = __inbyte(0x381);
if ( (v4 & 2) != 0 )
{
// ...
*(gDellGnvsPtr + 4144) = 2; // unchecked write (SMRAM corruption)
}
else
{
sub_7334(a1);
*(gDellGnvsPtr + 4144) = 1; // unchecked write (SMRAM corruption)
}
sub_5F58();
__outbyte(0x380, 0x83);
v8 = __inbyte(0x381);
v9 = 65;
if ( (v8 & 3) == 0 )
v9 = 45;
*(gDellGnvsPtr + 4146) = v9; // unchecked write (SMRAM corruption)
sub_5F58();
__outbyte(0x380, 0x83);
v10 = 897;
v11 = __inbyte(0x381);
result = v11 & 3;
if ( result )
v13 = (result - 1) <= 2;
else
v13 = 0;
v14 = gDellGnvsPtr;
*(gDellGnvsPtr + 4145) = v13; // unchecked write (SMRAM corruption)
v15 = (gDellGnvsPtr + 4144);
if ( gDellGnvsPtr != -4144 )
{
LOBYTE(v10) = 2;
LOBYTE(v14) = -82;
sub_5F94(v14, v10);
__outbyte(0x380, 0x83);
result = __inbyte(0x381);
if ( result == 1 )
{
*v15 = 1;
}
else if ( result == 2 )
{
*v15 = 2;
}
}
a1[5] = 0;
return result;
}
The GetVariable call initializes gDellGnvsPtr 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 multiple arbitrary write operations.
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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