SMM memory corruption vulnerability in SMM module on Fujitsu device (SMRAM write).
BINARLY efiXplorer team has discovered a SMM memory corruption vulnerability in a Fujitsu 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-2023-028
- Fujitsu PSIRT assigned CVE identifier: -
- AMI PSIRT assigned CVE identifier: -
- 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 AMI-based Fujitsu firmware images
The vulnerability was originally discovered on Fujitsu device mentioned below, however later it was confirmed by AMI PSIRT this issue is inside AMI's product.
| Device name | Unpacked firmware SHA256 | Firmware version | IBV | Module name | Module GUID | Module SHA256 | Module kind |
|---|---|---|---|---|---|---|---|
AU47 M1 | d3715136d50fc486ef59fb4aee1d7f06552fdf98423809939538fe905a1aa0b3 | V5.0.0.8-R1.40.0 | AMI | SmmRuntime | 7c79ac8c-5e6c-4e3d-ba6f-c260ee7c172e | 1be4cbba75688e77901f12cbe9964c69421ec13cc0493f12df2fc339e4b77a5d | SmmModule |
PRIMERGY RX4770 M2 | 083adc7cc324137950b4bc36308340e3b60b14ab97b7d967f33168930de4973c | V5.0.0.9-R1.20.0 | AMI | SmmRuntime | 7c79ac8c-5e6c-4e3d-ba6f-c260ee7c172e | 23c3e456e964e0667c2e17794c8b95715701ccdc5926cad4c86387f925c26b08 | SmmModule |
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Vulnerability description
Let's consider the vulnerability on the example of a module with SHA256 d3715136d50fc486ef59fb4aee1d7f06552fdf98423809939538fe905a1aa0b3.
The pseudocode of the vulnerable ChildSwSmiHandler function (with the HandlerType: EFI_SMM_RUNTIME_PROTOCOL_GUID) is presented below:
EFI_STATUS __fastcall ChildSwSmiHandler(
EFI_HANDLE DispatchHandle,
const void *Context,
char *CommBuffer,
UINTN *CommBufferSize)
{
__int64 Ptr; // [rsp+20h] [rbp-18h]
Ptr = *(CommBuffer + 4);
if ( Ptr )
{
(*(Ptr + 8))(*Ptr, gSmst, CommBuffer + 24);
*((_QWORD *)CommBuffer + 4) = 0; // Arbitrary write (*CommBufferSize is not checked)
}
return EFI_SUCCESS;
}
As we can see, input Communication Buffer is not validated to be outside of SMRAM since the Communication Buffer size (*CommBufferSize) is not checked to be valid (not 0 or equal to any fixed expectable value) for relying on the validation implemented in PiSmmCommunicationSmm module (based on a Communication Header).
In this way, a potential attacker can point CommBuffer just before SMRAM and set *CommBufferSize to 1 in order to pass validation in PiSmmCommunicationSmm and corrupt SMRAM (from SMRAM_BASE to SMRAM_BASE + 39).
In order to fix this vulnerability, check for *CommBufferSize should be added:
if (*CommBufferSize < sizeof(COMM_BUFFER_STRUCT)) {
// Error
}
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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 |
|---|---|
Fujitsu PSIRT is notified | 2023-12-22 |
BINARLY public disclosure date | 2024-05-15 |
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Acknowledgements
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