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An attacker with local privileged access can exploit this vulnerability to read the contents of the physical memory and use this information to exploit other vulnerabilities in DXE. A malicious code installed as a result of the vulnerability exploitation in a DXE driver could survive across an operating system (OS) boot process and runtime or modify NVRAM area on SPI flash storage (to gain persistence on target platform). Additionally, this vulnerability potentially could be used by threat actors to bypass OS security mechanisms (modify privileged memory or runtime variables), influence on the OS boot process, and in some cases would allow an attacker to hook or modify EFI Runtime services.
Binarly REsearch Team has discovered multiple memory leaks / information disclosure vulnerabilities in the DXE driver due to improper input validation during PCX file processing in Insyde firmware.
An attacker with local privileged access can exploit this vulnerability to read the contents of the physical memory and use this information to exploit other vulnerabilities in DXE. A malicious code installed as a result of the vulnerability exploitation in a DXE driver could survive across an operating system (OS) boot process and runtime or modify NVRAM area on SPI flash storage (to gain persistence on target platform). Additionally, this vulnerability potentially could be used by threat actors to bypass OS security mechanisms (modify privileged memory or runtime variables), influence on the OS boot process, and in some cases would allow an attacker to hook or modify EFI Runtime services.
The pseudocode of the vulnerable function is shown below:
unsigned __int64 __fastcall DecodePCX(
PCXHeader *Image,
__int64 ImageSize,
__int64 *a3,
unsigned __int64 *a4,
_QWORD *a5,
unsigned __int64 *a6)
{
__int64 v6; // rbx
unsigned __int64 v8; // r14
__int64 Index; // rbp
unsigned __int64 v10; // rsi
__int64 v11; // r15
char *v12; // rdx
unsigned __int64 i; // rcx
char v14; // al
unsigned __int64 v15; // r15
__int64 v16; // rcx
__int64 v17; // rax
__int64 v18; // rdx
__int64 v19; // rcx
__int64 v20; // r8
__int64 v21; // r9
__int64 v22; // r12
unsigned __int64 v23; // r14
__int64 v24; // rcx
__int64 v25; // rax
__int64 v26; // rdx
unsigned __int64 v27; // rcx
unsigned __int64 v28; // r8
EFI_PHYSICAL_ADDRESS v29; // rsi
_QWORD *v30; // rax
__int64 v31; // r9
unsigned __int64 v32; // r10
EFI_PHYSICAL_ADDRESS v34; // r15
unsigned __int64 v35; // rax
unsigned __int64 v36; // r11
EFI_PHYSICAL_ADDRESS v37; // r15
char v38; // al
__int64 v40; // rcx
__int64 v41; // rdx
unsigned __int64 v42; // rdx
unsigned __int64 j; // r8
__int64 bytes_per_line; // [rsp+20h] [rbp-458h]
unsigned __int64 v45; // [rsp+30h] [rbp-448h]
_BYTE v46[1080]; // [rsp+40h] [rbp-438h]
unsigned __int64 Total; // [rsp+480h] [rbp+8h]
v6 = 0i64;
v8 = 0i64;
Index = 0i64;
v10 = 0i64;
if ( *&Image->id != 1290 )
return 0x8000000000000003ui64;
if ( Image->encoding != 1 )
return 0x8000000000000003ui64;
if ( Image->bits_per_px != 8 )
return 0x8000000000000003ui64;
// Root cause for all vulnerabilities is here:
// Image->planes and Image->bytes_per_line are not validated
// => Total is controllable by the attacker
// It will lead to OOB Reads further
// BRLY-LOGOFAIL-2023-011: Improper input validation leads to OOB Read vulnerabilities
*a6 = Image->x_max - Image->x_min + 1;
v11 = Image->y_max - Image->y_min + 1;
*a5 = v11;
bytes_per_line = Image->bytes_per_line;
v12 = Image + ImageSize - 767;
Total = bytes_per_line * Image->planes;
for ( i = 0i64; i < 0x100; ++i )
{
v46[4 * i + 2] = *(v12 - 1);
v14 = *v12;
v12 += 3;
v46[4 * i + 1] = v14;
v46[4 * i] = *(v12 - 2);
v46[4 * i + 3] = 0;
}
v15 = 4 * *a6 * v11;
v45 = v15;
if ( v15 >= 0x100000000i64 )
return 0x8000000000000003ui64;
if ( sub_964(i, v12, a3, a4) )
v17 = sub_9B4(v16, (v15 >> 12) + ((v15 & 0xFFF) != 0));
else
v17 = sub_9EC(v16, v15);
v22 = v17;
if ( v17 )
{
if ( (Image->planes - 3) > 1u || Image->bits_per_px != 8 )
{
v40 = *a6;
if ( *a5 * *a6 )
{
do
{
// Vulnerability:
// if v10 == v40, the Index will be incremented by a controllable
// number of times since attacker is controlling
// Total = Image->bytes_per_line * Image->planes;
// and fields Image->bytes_per_line and Image->planes are unvalidated
// So, we have OOB Read here: Image->Buffer[Index]
if ( v10 == v40 )
{
if ( v10 < Total )
{
v40 = *a6;
Index += Total - v10;
}
v10 = 0i64;
}
v41 = Image->Buffer[Index];
if ( (Image->Buffer[Index] & 0xC0) == 0xC0 )
{
v42 = v41 & 0x3F;
++Index;
for ( j = 0i64; j < v42; ++j )
{
++v10;
*(v17 + 4 * v8++) = *&v46[4 * Image->Buffer[Index]];
v40 = *a6;
if ( v10 == *a6 )
break;
}
}
else
{
*(v17 + 4 * v8++) = *&v46[4 * v41];
v40 = *a6;
++v10;
}
++Index;
}
while ( v8 < *a5 * v40 );
}
*a3 = v17;
*a4 = v15;
return 0i64;
}
v23 = Total + 50;
if ( sub_964(v19, v18, v20, v21) )
v25 = sub_9B4(v24, (v23 >> 12) + ((v23 & 0xFFF) != 0));
else
v25 = sub_9EC(v24, v23);
v29 = v25;
if ( v25 )
v29 = sub_310(v25, v23);
if ( v29 )
{
v30 = a5;
v31 = 0i64;
if ( *a5 )
{
v32 = Total;
while ( 1 )
{
v27 = 0i64;
if ( v32 )
{
do
{
// Vulnerability:
// The Index will be incremented by a controllable
// number of times since attacker is controlling
// Total = Image->bytes_per_line * Image->planes;
// and fields Image->bytes_per_line and Image->planes are unvalidated
// So, we have OOB Read here: Image->Buffer[Index]
v28 = Image->Buffer[Index];
v26 = 1i64;
if ( (Image->Buffer[Index] & 0xC0) == 0xC0 )
{
LOBYTE(v28) = Image->Buffer[Index + 1];
v26 = Image->Buffer[Index++] & 0x3F;
}
while ( v27 < v32 )
{
if ( !v26-- )
break;
*(v27 + v29) = v28;
++v27;
}
++Index;
}
while ( v27 < v32 );
v30 = a5;
}
if ( Image->planes == 3 )
{
v28 = 0i64;
if ( *a6 )
{
v34 = v29 + 2 * bytes_per_line;
do
{
v26 = v34 + v28;
*(v22 + 4 * (v28 + v31 * *a6) + 2) = *(v34 + v28 - 2 * bytes_per_line);
*(v22 + 4 * (v28 + v31 * *a6) + 1) = *(v34 + v28 - bytes_per_line);
v27 = v28 + v31 * *a6;
*(v22 + 4 * v27) = *(v34 + v28);
v35 = v28 + v31 * *a6;
++v28;
*(v22 + 4 * v35 + 3) = -1;
}
while ( v28 < *a6 );
LABEL_37:
v30 = a5;
v32 = Total;
}
}
else
{
v36 = 0i64;
if ( *a6 )
{
v37 = v29 + 2 * bytes_per_line;
v28 = -bytes_per_line;
do
{
v26 = v37 + v36;
*(v22 + 4 * (v36 + v31 * *a6) + 2) = *(v37 + v36 - 2 * bytes_per_line);
*(v22 + 4 * (v36 + v31 * *a6) + 1) = *(v37 + v36 - bytes_per_line);
*(v22 + 4 * (v36 + v31 * *a6)) = *(v37 + v36);
v38 = *(v37 + v36 + bytes_per_line);
v27 = v36 + v31 * *a6;
++v36;
*(v22 + 4 * v27 + 3) = v38;
}
while ( v36 < *a6 );
goto LABEL_37;
}
}
if ( ++v31 >= *v30 )
{
v23 = Total + 50;
v15 = v45;
break;
}
}
}
*a3 = v22;
*a4 = v15;
if ( sub_964(v27, v26, v28, v31) )
{
LOBYTE(v6) = (v23 & 0xFFF) != 0;
gBS->FreePages(v29, (v23 >> 12) + v6);
}
else
{
(gBS->FreePool)(v29);
}
return 0i64;
}
}
return 0x8000000000000009ui64;
}As we can see from the pseudocode, Image->planes and Image->bytes_per_line values are not validated. As a result, the Total value is controllable by the attacker and unchecked value.
The fact that Total is controlled by the attacker and unchecked can lead to OOB read at 3 locations (documented in the pseudocode above).
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.
Binarly REsearch Team
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