CVE-2020-6152
A code execution vulnerability exists in the DICOM parse_dicom_meta_info functionality of Accusoft ImageGear 19.7. A specially crafted malformed file can cause an out-of-bounds write. An attacker can trigger this vulnerability by providing a victim with a malicious DICOM file.
The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.
Accusoft ImageGear 19.7
ImageGear - https://www.accusoft.com/products/imagegear-collection/
9.8 - CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE-252 - Unchecked Return Value
The ImageGear library is a document imaging developer toolkit that offers image conversion, creation, editing, annotation and more. It supports more than 100 formats, including many image formats, DICOM, PDF, Microsoft Office and others.
There is a vulnerability in the parse_dicom_meta_info function which occurs with a specially crafted DICOM file leading to an out-of-bounds write which can result in remote code execution.
Trying to load a malformed DICOM file, we end up in the following situation:
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=deadfad0 ecx=00000012 edx=010c5000 esi=00020003 edi=deadface
eip=0a5c838f esp=00fbf23c ebp=00fbf39c iopl=0 nv up ei pl nz na po nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00010202
igMED19d!CPb_MED_init+0x152ef:
0a5c838f c6040700 mov byte ptr [edi+eax],0 ds:0023:deadface=??
The pseudo code responsible to parse the dicom meta information is described below.
void __cdecl parse_dicom_meta_info(mys_table_function *file_operations,mys_dicom_to_determine *param_2,undefined8 *param_3)
{
bool bVar1;
uint uVar2;
int iVar3;
undefined4 offset_in_file;
int variable;
int status_get_dicom_tag;
uint *puVar4;
uint allocation_size;
int status;
mys_table_function *_file_operations;
int iVar5;
byte *pbVar6;
uint _size_from_tag_data;
int local_150;
uint size_from_tag;
uint index_vr_code;
int local_144;
int local_140;
uint dicom_tag_id;
int local_138;
uint local_134;
int local_130;
int local_12c;
byte *ptr_buffer_allocated;
int local_120;
undefined8 local_11c;
undefined8 local_114;
undefined4 local_10c;
byte preambule_buffer [256];
uint local_8;
local_8 = DAT_10050fe0 ^ (uint)&stack0xfffffffc;
local_12c = 0;
ptr_buffer_allocated = (byte *)0x0;
local_140 = 0;
local_120 = 0;
bVar1 = false;
local_138 = 0;
local_11c = 0;
local_114 = 0;
local_10c = 0;
memset(preambule_buffer,0,0x100);
(*_igcore19d!set_endian)(file_operations,0);
(*_igcore19d!set_file_pointer_related)(file_operations,0,0);
(*_igcore19d!read_data_into_buffer)(file_operations,preambule_buffer,0x80);
copy_preambule_buffer(param_2,preambule_buffer,0x80);
(*_igcore19d!set_file_pointer_related)(file_operations,4,1);
local_134 = 0;
offset_in_file = (*_igcore19d!possible_get_current_offset)(file_operations);
variable = FUN_1000ab00(file_operations,1,3,&dicom_tag_id,0);
(*_igcore19d!set_file_pointer_related)(file_operations,offset_in_file,0);
local_144 = 0;
status = 0;
do { [1]
_file_operations = file_operations;
iVar5 = variable;
status_get_dicom_tag =
get_dicom_tag_info(file_operations,variable,&dicom_tag_id,&index_vr_code,&size_from_tag, [4]
&local_130);
iVar3 = local_130;
uVar2 = dicom_tag_id;
_size_from_tag_data = size_from_tag; [5]
if (status_get_dicom_tag == 0) {
iVar5 = 0x5622;
_file_operations = (mys_table_function *)0x1225;
goto display_error;
}
if (status != 0) {
local_120 = local_120 + local_130;
}
puVar4 = &DAT_10044008;
do {
if (*puVar4 == dicom_tag_id) {
local_138 = local_138 + 1;
break;
}
puVar4 = puVar4 + 1;
} while ((int)puVar4 < 0x10044020);
if ((short)(dicom_tag_id >> 0x10) == 2) { [6]
if ((ushort)dicom_tag_id < (ushort)local_134) {
iVar5 = 0x5625;
_file_operations = (mys_table_function *)0x124c;
display_error:
(*(code *)igcore19d!display_error_message)
("..\\..\\..\\..\\Common\\Components\\MED\\Dicom\\dcmread.c",_file_operations,
iVar5);
goto LAB_1001846a;
}
allocation_size = size_from_tag + 2;
if (0x100 < allocation_size) { [7]
status = perform_checking(dicom_tag_id,(short)index_vr_code,size_from_tag);
if (status == 0) {
iVar5 = 0x5614;
_file_operations = (mys_table_function *)0x1264;
}
else {
allocation_size = allocate_mem(param_2,allocation_size,&ptr_buffer_allocated); [8]
if (allocation_size == 0) goto read_operations;
}
goto display_error;
}
ptr_buffer_allocated = preambule_buffer; [9]
read_operations:
status = perform_some_read_operations(file_operations,uVar2,_size_from_tag_data,index_vr_code,ptr_buffer_allocated, &local_134,&local_130); [14]
if (status == 0) {
iVar5 = 0x5624;
_file_operations = (mys_table_function *)0x126e;
goto display_error;
}
ptr_buffer_allocated[_size_from_tag_data] = 0; [3]
[...]
}
[...]
} while( true ); [2]
}
The function parse_dicom_meta_info is responsible for processing the dicom file through a do-while loop [1] & [2] to parse the meta info. In our case it’s crashing in [3] because ptr_buffer_allocated is null. We can control the _size_from_tag_data directly from the crafted file. Now let’s understand how we can reach this state in detail.
First, a call to the function get_dicom_tag_info in [4] fills several important variables : size_from_tag , dicom_tag_id and index_vr_code.
The size_from_tag and dicom_tag_id are directly read from the file data itself, when index_vr_code is corresponding to an index of table of different Value Representation (VR). In our case the interesting Value Representation is ‘SQ’ for Sequence and associated to an index of ‘12’. The ‘SQ’ Value Representation is interesting to us because it doesn’t have an enforced length value defined by the DICOM specification.
In [5] _size_from_tag_data is assigned the content of size_from_tag directly. The dicom_tag_id is used to verify the processing of tag IDs corresponding to the 0x0002 group in [6].
According to the allocation_size, which is just size_from_tag + 2, a test [7] is performed to decide if ptr_buffer_allocated will be assigned the result of a memory allocation in [8] or if it will be assigned the local buffer preambule_buffer in [9]. Because of this, ptr_buffer_allocated can become null only through the allocate_mem function.
We need to go deeper into the function allocate_mem described below, which is calling in [10] AF_memm_alloc, described just after.
uint allocate_mem(mys_dicom_to_determine *param_1,size_t size,byte **ptr_ptr_buff)
{
byte *ptr_buff;
uint uVar1;
if ((param_1 == (mys_dicom_to_determine *)0x0) || (param_1->constant_0xdeadadde != -0x21525222)) {
(*(code *)igcore19d!display_error_message)
("..\\..\\..\\..\\Common\\Components\\MED\\Dicom\\DataSet.c",0x580,0x5613,0,0,param_1,
0);
}
else {
*ptr_ptr_buff = (byte *)0x0; [14]
if (param_1 == (mys_dicom_to_determine *)0xffffffb4) {
*ptr_ptr_buff = (byte *)0x0;
}
else {
ptr_buff = (byte *)(*_igCore19d!AF_memm_alloc) [10]
(*(undefined4 *)¶m_1->kind_of_heap,size,
"..\\..\\..\\..\\Common\\Components\\MED\\Dicom\\DataSet.c",
0x567);
if (ptr_buff != (byte *)0x0) { [13]
*ptr_ptr_buff = ptr_buff;
memset(ptr_buff,0,size);
}
}
}
/* WARNING: Could not recover jumptable at 0x1000e963. Too many branches */
/* WARNING: Treating indirect jump as call */
uVar1 = (*_igcore19d!perform_some_memory_operations)();
return uVar1;
}
void * __thiscall AF_memm_alloc(undefined4 this,uint param_2,size_t size)
{
int iVar1;
uint *puVar2;
void *_Memory;
uint *puVar3;
undefined4 *_Dst;
int iVar4;
uint uVar5;
uint *_Dst_00;
wrapper_EnterCriticalSection(*(LPCRITICAL_SECTION *)(Count_CriticalSectionUse + 0x1684));
_Memory = MSVCR110.DLL::malloc(size); [12]
if (_Memory == (void *)0x0) {
wrapper_LeaveCriticalSection(*(LPCRITICAL_SECTION *)(Count_CriticalSectionUse + 0x1684));
return (void *)0x0; [11]
}
[...]
}
A null return value can occur in AF_memm_alloc [11] only if MSVCR110.DLL::malloc is failing [12] . When this happens, the test in [13] will not succeed and *ptr_ptr_buf is left untouched, meaning that its value is 0, as it was initialized in [14].
Now we get back into parse_dicom_meta_info with a null value for ptr_buffer_allocated, the index_vr_code will help to avoid an exception in the function perform_some_read_operations in [14] before leading to the crash.
Because an attacker controls the value for size_from_tag (and thus also allocation_size), the malloc at [12] can fail by supplying an arbitrary large value. Later, the 0-write at [3] can be controlled using allocation_size, because ptr_buffer_allocated will be null.
Crash output:
0:000> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
KEY_VALUES_STRING: 1
Key : AV.Fault
Value: Write
Key : Analysis.CPU.Sec
Value: 1
Key : Analysis.DebugAnalysisProvider.CPP
Value: Create: 8007007e on DESKTOP-451082P
Key : Analysis.DebugData
Value: CreateObject
Key : Analysis.DebugModel
Value: CreateObject
Key : Analysis.Elapsed.Sec
Value: 5
Key : Analysis.Memory.CommitPeak.Mb
Value: 85
Key : Analysis.System
Value: CreateObject
Key : Timeline.OS.Boot.DeltaSec
Value: 151001
Key : Timeline.Process.Start.DeltaSec
Value: 132
ADDITIONAL_XML: 1
NTGLOBALFLAG: 2100000
APPLICATION_VERIFIER_FLAGS: 0
APPLICATION_VERIFIER_LOADED: 1
EXCEPTION_RECORD: (.exr -1)
ExceptionAddress: 0a5c838f (igMED19d!CPb_MED_init+0x000152ef)
ExceptionCode: c0000005 (Access violation)
ExceptionFlags: 00000000
NumberParameters: 2
Parameter[0]: 00000001
Parameter[1]: deadface
Attempt to write to address deadface
FAULTING_THREAD: 00001510
PROCESS_NAME: Fuzzme.exe
WRITE_ADDRESS: deadface
ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced memory at 0x%p. The memory could not be %s.
EXCEPTION_CODE_STR: c0000005
EXCEPTION_PARAMETER1: 00000001
EXCEPTION_PARAMETER2: deadface
STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be wrong.
00fbf39c 0a5cb44f 00fbf4f4 07b62fa0 00fbf428 igMED19d!CPb_MED_init+0x152ef
00fbf3c4 0a5c6747 00fbf4f4 07b62fa0 10000023 igMED19d!CPb_MED_init+0x183af
00fbf46c 027410d9 00fbf4f4 0776cfb8 00000001 igMED19d!CPb_MED_init+0x136a7
00fbf4a4 02780557 00000000 0776cfb8 00fbf4f4 igCore19d!IG_image_savelist_get+0xb29
00fbf720 0277feb9 00000000 05fb3fe0 00000001 igCore19d!IG_mpi_page_set+0x14807
00fbf740 02715777 00000000 05fb3fe0 00000001 igCore19d!IG_mpi_page_set+0x14169
00fbf760 00961372 05fb3fe0 00fbf77c 05facf80 igCore19d!IG_load_file+0x47
00fbf788 00961778 05fb3fe0 00fbf7f0 00000021 Fuzzme!fuzzme+0x162
00fbf818 00961f7d 00000005 05facf80 02f44f48 Fuzzme!fuzzme+0x568
00fbf860 7744e2f9 010c4000 7744e2e0 00fbf8cc Fuzzme!fuzzme+0xd6d
00fbf870 77c727c7 010c4000 c1489ff1 00000000 KERNEL32!BaseThreadInitThunk+0x19
00fbf8cc 77c7279b ffffffff 77cb2d62 00000000 ntdll!__RtlUserThreadStart+0x2b
00fbf8dc 00000000 00962005 010c4000 00000000 ntdll!_RtlUserThreadStart+0x1b
STACK_COMMAND: ~0s ; .cxr ; kb
SYMBOL_NAME: igMED19d!CPb_MED_init+152ef
MODULE_NAME: igMED19d
IMAGE_NAME: igMED19d.dll
FAILURE_BUCKET_ID: NULL_POINTER_WRITE_AVRF_c0000005_igMED19d.dll!CPb_MED_init
OS_VERSION: 10.0.17763.1
BUILDLAB_STR: rs5_release
OSPLATFORM_TYPE: x86
OSNAME: Windows 10
FAILURE_ID_HASH: {45a639e4-203c-d375-5c67-d4bd7ae4ad96}
Followup: MachineOwner
---------
2020-06-23 - Vendor Disclosure
2020-09-01 - Public Release
Discovered by Emmanuel Tacheau of Cisco Talos.