Memory contents leak / information disclosure vulnerability in DXE driver on Dell platform.
BINARLY efiXplorer team has discovered a memory contents leak / information disclosure vulnerability that allows a potential attacker to dump stack memory or global memory into an NVRAM variable. This in turn could help building a successful attack vector based on exploiting a memory corruption vulnerability.
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Potential Impact
An attacker with high local access can exploit this vulnerability to read the contents of stack memory or global memory. This information could help with exploitation of other vulnerabilities in DXE 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.
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Vulnerability Information
- BINARLY internal vulnerability identifier: BRLY-2022-174
- AMD PSIRT assigned CVE identifier: CVE-2023-20597
- CVSS v3.1: 6.0 Medium AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N
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Affected Dell firmware
| Product | Firmware version | CPU | Module name | Module GUID | Module SHA256 |
|---|---|---|---|---|---|
Inspiron 15 3525,Vostro 3525,Vostro 3425 | 0.1.3.0 | AMD | AmdCcxZen3CznDxe | 56aa1233-7407-4058-9e17-88de138ea15d | fd8ddad069d3583eef335a4deed2906bf3b24fce19a7c8d51dc1606b326b5411 |
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Vulnerability description
Let's take Inspiron 15 3525,Vostro 3525,Vostro 3425's firmware (version: 0.1.3.0, module sha256: fd8ddad069d3583eef335a4deed2906bf3b24fce19a7c8d51dc1606b326b5411) as an example.
The following code in the module actually allows leaking memory:
- a call to a
gRT->GetVariable()offset:0x2827 - a call to a
gRT->SetVariable()offset:0x285f
void sub_27C0()
{
int v0; // eax
__int64 v1; // rax
int v2[4]; // [rsp+30h] [rbp-10h] BYREF
char v3; // [rsp+50h] [rbp+10h] BYREF
char v4; // [rsp+58h] [rbp+18h] BYREF
__int64 v5; // [rsp+60h] [rbp+20h] BYREF
sub_4C6C(1024i64, " CcxCheckDownCoreStatus Entry\n");
v2[0] = 41014;
v0 = sub_5974(v2);
v3 = 0;
v5 = 1i64;
v4 = v0 == 0;
v1 = (gRT->GetVariable)( // <= first call (we can rewrite DataSize here)
L"DownCoreStatus",
&VendorGuid,
0i64,
&v5,
&v3);
if ( v4 != v3 || v1 )
{
(gRT->SetVariable)( // <= second call
L"DownCoreStatus",
&VendorGuid,
7i64,
v5,
&v4);
if ( v3 && !v4 )
{
sub_4C6C(1024i64, aDowncoredAutoI);
(gRT->ResetSystem)(0i64, 0i64, 0i64, 0i64);
}
}
sub_4C6C(1024i64, aCcxcheckdownco_0);
}
The gRT->SetVariable() service is called with the DataSize as an argument, which will be overwritten inside the gRT->GetVariable() service if the length of DownCoreStatus NVRAM variable is greater than 1.
Thus, a potential attacker can dump X - 1 bytes from the stack (or global memory) into DownCoreStatus NVRAM variable by setting DownCoreStatus NVRAM variable's size to X > 1.
To fix this vulnerability the DataSize must be re-initialized with the size of DownCoreStatus before calling gRT->SetVariable().
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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 (YYYY-mm-dd) |
|---|---|
Dell PSIRT is notified | 2022-12-29 |
AMD PSIRT assigned CVE number | 2023-06-06 |
AMD PSIRT provide patch release | 2023-09-20 |
BINARLY public disclosure date | 2023-09-21 |
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Acknowledgements
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