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Binarly Advisories

[BRLY-2022-100] Memory contents leak / information disclosure vulnerability in DXE driver on Dell platform.

Summary

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.

Vulnerability Information

Affected Dell firmware with confirmed impact by Binarly team

Product Firmware version CPU Module name Module GUID Module SHA256
Latitude 9420, Latitude 9420 0.1.16.2 Intel DynamicUpdatePDTDxe 440bd554-fa04-4b26-b099-188a3e724b20 22c8db2e39fa0ad26f38e77f32a2e86d16e50465654ffeb9a0124006d1584fc2
Latitude 9420, Latitude 9420 0.1.16.2 Intel DynamicUpdatePDTDxe 440bd554-fa04-4b26-b099-188a3e724b20 22c8db2e39fa0ad26f38e77f32a2e86d16e50465654ffeb9a0124006d1584fc2
Latitude 9510 0.1.16.0 Intel 440BD554-FA04-4B26-B099-188A3E724B20 440bd554-fa04-4b26-b099-188a3e724b20 4e00ff7aab780ea693ced1222a18f13139f9b4b30f3bbfb9e522d3248d5bd017
Latitude 9510 0.1.16.0 Intel 440BD554-FA04-4B26-B099-188A3E724B20 440bd554-fa04-4b26-b099-188a3e724b20 4e00ff7aab780ea693ced1222a18f13139f9b4b30f3bbfb9e522d3248d5bd017
Precision 5470 0.1.8.0 Intel DynamicUpdatePDTDxe 440bd554-fa04-4b26-b099-188a3e724b20 4fec0aa417a431da9d8f609278b8e94bc7e3ffafb61cf415ffe898ec429ae252
Precision 5470 0.1.8.0 Intel DynamicUpdatePDTDxe 440bd554-fa04-4b26-b099-188a3e724b20 4fec0aa417a431da9d8f609278b8e94bc7e3ffafb61cf415ffe898ec429ae252
Precision 5470 0.1.8.0 Intel DynamicUpdatePDTDxe 440bd554-fa04-4b26-b099-188a3e724b20 4fec0aa417a431da9d8f609278b8e94bc7e3ffafb61cf415ffe898ec429ae252
Precision 7X50 0.1.19.0 Intel 440BD554-FA04-4B26-B099-188A3E724B20 440bd554-fa04-4b26-b099-188a3e724b20 a7db870ba9f51b1e9cfeac2fab02511bd4aa70f025c522ad3f82c3aa4173f6b0
Latitude 9410 0.1.18.0 Intel 440BD554-FA04-4B26-B099-188A3E724B20 440bd554-fa04-4b26-b099-188a3e724b20 f667101460ff0497cd4520d58b7d65177feb14833bf66939e2eb5ce08e645c1c
Latitude 9410 0.1.18.0 Intel 440BD554-FA04-4B26-B099-188A3E724B20 440bd554-fa04-4b26-b099-188a3e724b20 f667101460ff0497cd4520d58b7d65177feb14833bf66939e2eb5ce08e645c1c

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 explotation 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.

Vulnerability description

Let's take Latitude 9420, Latitude 9420's firmware (version: 0.1.16.2, module sha256: 22c8db2e39fa0ad26f38e77f32a2e86d16e50465654ffeb9a0124006d1584fc2) as an example.

The following code in the module actually allows leaking memory:

void __fastcall NotifyFunction(EFI_CAPSULE_HEADER **Event, void *Context)
{
  unsigned __int64 i; // rdi
  __int64 v4; // r8
  __int64 v5; // r8
  __int64 v6; // rax
  unsigned __int64 v7; // [rsp+40h] [rbp-9h] BYREF
  __int64 v8; // [rsp+48h] [rbp-1h] BYREF
  __int64 v9; // [rsp+50h] [rbp+7h] BYREF
  __int64 v10; // [rsp+58h] [rbp+Fh] BYREF
  __int64 v11; // [rsp+60h] [rbp+17h] BYREF
  __int64 v12; // [rsp+68h] [rbp+1Fh] BYREF
  char *v13; // [rsp+70h] [rbp+27h] BYREF
  _BYTE v14[16]; // [rsp+78h] [rbp+2Fh] BYREF
  __int64 v15[3]; // [rsp+88h] [rbp+3Fh] BYREF
  unsigned __int16 v16; // [rsp+C0h] [rbp+77h] BYREF
  int v17; // [rsp+C8h] [rbp+7Fh] BYREF

  v12 = 0i64;
  v8 = 0i64;
  v9 = 0i64;
  v10 = 0i64;
  v11 = 0i64;
  v17 = 0;
  if ( ((__int64 (__fastcall *)(__int64, EFI_GUID *, _QWORD, unsigned __int64 *, __int64 *))gBS->LocateHandleBuffer)(
         2i64,
         &EFI_FIRMWARE_VOLUME2_PROTOCOL_GUID,
         0i64,
         &v7,
         v15) >= 0
    && v7 )
  {
    v9 = 15i64;
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, _QWORD, __int64 *, _BYTE *))gRT->GetVariable)(// <= first call (we can rewrite DataSize here)
      L"MPDTContent",
      &NameGuid,
      0i64,
      &v9,
      v14);
    for ( i = 0i64; i < v7; ++i )
    {
      if ( ((__int64 (__fastcall *)(_QWORD, EFI_GUID *, __int64 *))gBS->HandleProtocol)(
             *(_QWORD *)(v15[0] + 8 * i),
             &EFI_FIRMWARE_VOLUME2_PROTOCOL_GUID,
             &v11) < 0 )
        goto LABEL_18;
      LOBYTE(v4) = 25;
      if ( (*(__int64 (__fastcall **)(__int64, EFI_GUID *, __int64, _QWORD, __int64 *, __int64 *, int *))(v11 + 24))(
             v11,
             &NameGuid,
             v4,
             0i64,
             &v12,
             &v8,
             &v17) >= 0 )
      {
        ((void (__fastcall *)(__int64, __int64, __int64 *))gBS->AllocatePool)(4i64, v8, &v10);
        v10 = v12;
        v13 = 0i64;
        v16 = 0;
        if ( v12 )
        {
          v6 = sub_C58(v14[1], v12, v8, &v16, (unsigned int **)&v13, v12);
          if ( v6 >= 0 )
          {
            if ( v13 )
              v6 = sub_EF8(v13, v16);
            else
              v6 = 0x8000000000000002ui64;
          }
          v5 = v6;
          if ( v6 >= 0 )
            continue;
        }
        else
        {
          v5 = 0x8000000000000015ui64;
        }
        sub_4E0((__int64)v14, 129, v5);
      }
    }
    ((void (__fastcall *)(const __int16 *, EFI_GUID *, __int64, __int64, _BYTE *))gRT->SetVariable)(
      L"MPDTContent",
      &NameGuid,
      7i64,
      v9,
      v14);
    if ( i >= v7 )
      ((void (__fastcall *)(EFI_CAPSULE_HEADER **))gBS->CloseEvent)(Event);
    ((void (__fastcall *)(__int64))gBS->FreePool)(v10);
  }
LABEL_18:
  ((void (__fastcall *)(EFI_CAPSULE_HEADER **))gBS->CloseEvent)(Event);
}

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 MPDTContent NVRAM variable is greater than 15.

Thus, a potential attacker can dump X - 15 bytes from the stack (or global memory) into MPDTContent NVRAM variable by setting MPDTContent NVRAM variable's size to X > 15.

To fix this vulnerability the DataSize must be re-initialized with the size of MPDTContent before calling gRT->SetVariable().

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
Dell PSIRT confirmed reported issue 2023-03-16
Dell PSIRT assigned CVE number 2023-06-15
Dell PSIRT provide patch release 2023-06-15
BINARLY public disclosure date 2023-06-21

Acknowledgements

BINARLY efiXplorer team

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