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Multiple Advantech WebAccess Vulnerabilities

Critical
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Synopsis

Tenable found multiple unauthenticated, remote stack overflow vulnerabilities in Advantech WebAccess/SCADA 8.4.0.

CVE-2019-3953: Unauthenticated Remote Stack Buffer Overflow (IOCTL 10012)

The flaw exists in viewsrv.dll due to improper validation of user-supplied data before copying the data to a fixed size stack buffer when processing an IOCTL 10012 RPC call. 

.text:10001CDC      mov     esi, [ebp+arg_pInbuf] ; attacker-controlled data
.text:10001CDF      lea     eax, [esi+4]
.text:10001CE2      push    eax
.text:10001CE3      lea     ecx, [ebp+var_BroadwinPath]
.text:10001CE9      push    ecx
.text:10001CEA      push    offset aSSBwextra_ini ; "%s%s\\bwextra.ini"
.text:10001CEF      lea     edx, [ebp+var_file]   ; copying attacker-controlled data
.text:10001CEF                                    ; to a fixed-size buf on the
.text:10001CEF                                    ; stack ==> stack overflow !!!
.text:10001CF5      push    edx
.text:10001CF6      call    ds:sprintf

Windbg output:

(2dbd8.2df70): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=00000001 ecx=41414141 edx=00000000 esi=00000000 edi=030bd4b4
eip=41414141 esp=030bcec8 ebp=41414141 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
41414141 ??              ???
0:007> kb
ChildEBP RetAddr  Args to Child              
WARNING: Frame IP not in any known module. Following frames may be wrong.
030bcec4 41414141 41414141 41414141 41414141 0x41414141
030bcec8 41414141 41414141 41414141 41414141 0x41414141
030bcecc 41414141 41414141 41414141 41414141 0x41414141
030bced0 41414141 41414141 41414141 41414141 0x41414141
030bced4 41414141 41414141 41414141 41414141 0x41414141
030bced8 41414141 41414141 41414141 41414141 0x41414141
...
030bcf98 41414141 41414141 77625c41 72747865 0x41414141
030bcf9c 41414141 77625c41 72747865 6e692e61 0x41414141
030bcfa0 77625c41 72747865 6e692e61 00000069 0x41414141
030bcfa4 72747865 6e692e61 00000069 00000000 0x77625c41
030bcfa8 6e692e61 00000069 00000000 00000000 0x72747865
030bcfac 00000000 00000000 00000000 00000000 0x6e692e61
0:007> .load "MSEC.dll"
0:007> !exploitable

!exploitable 1.6.0.0
Exploitability Classification: EXPLOITABLE
Recommended Bug Title: Exploitable - Data Execution Prevention Violation starting at Unknown Symbol @ 0x0000000041414141 called from Unknown Symbol @ 0x000000006e692e61 (Hash=0x83f3e768.0xed88845e)

User mode DEP access violations are exploitable.

CVE-2019-3954: Unauthenticated Remote Stack Buffer Overflow (IOCTL 81024)

The flaw exists in the VdBroadWinGetLocalDataLogEx() function in viewdll1.dll due to improper validation of user-supplied data before copying the data to a fixed-size stack-based buffer when processing an IOCTL 81024 RPC message. 

.text:1001671C      mov     edx, [ebp+var_pNode] ; attacker_controlled
.text:10016722      push    edx
.text:10016723      mov     eax, [ebp+var_pProject] ; attacker_controlled
.text:10016729      push    eax
.text:1001672A      lea     ecx, [ebp+var_ModuleFileName]
.text:10016730      push    ecx
.text:10016731      push    offset aSS_SSysinfo_in ; "%s%s_%s\\sysinfo.ini"
.text:10016736      lea     edx, [ebp+var_634] ; copying attacker-controlled data
.text:10016736                               ; to a fixed-size buffer on the
.text:10016736                               ; stack ==> stack overflow!
.text:1001673C      push    edx
.text:1001673D      call    ds:sprintf

Windbg output: 

(38084.39638): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=41414141 ebx=0319e674 ecx=00000073 edx=7ffffffe esi=01edb97c edi=41414141
eip=74eed193 esp=0319e3d0 ebp=0319e654 iopl=0         nv up ei pl nz na po nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010202
msvcrt!_output_l+0x9fd:
74eed193 803800          cmp     byte ptr [eax],0           ds:002b:41414141=??
0:008> kb
ChildEBP RetAddr  Args to Child              
0319e654 74efd399 0319e674 01edb978 00000000 msvcrt!_output_l+0x9fd
*** WARNING: Unable to verify checksum for C:\WebAccess\Node\viewdll1.dll
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for C:\WebAccess\Node\viewdll1.dll - 
0319e694 01ed67c3 0319e920 01edb978 0319ed44 msvcrt!sprintf+0x5a
WARNING: Stack unwind information not available. Following frames may be wrong.
0319ee48 41414141 41414141 41414141 41414141 viewdll1!VdBroadWinGetLocalDataLogEx+0x15a
0319ee4c 41414141 41414141 41414141 41414141 0x41414141
0319ee50 41414141 41414141 41414141 41414141 0x41414141
0319ee54 41414141 41414141 41414141 41414141 0x41414141
...
0:008> .load msec.dll
0:008> !exploitable

!exploitable 1.6.0.0
Exploitability Classification: EXPLOITABLE
Recommended Bug Title: Exploitable - Exception Handler Chain Corrupted starting at msvcrt!_output_l+0x00000000000009fd (Hash=0xa92188c6.0xc8febe8f)

Corruption of the exception handler chain is considered exploitable

Solution

Upgrade to version 8.4.1 or later.

Disclosure Timeline

04/24/2019 - Vulnerability 1 discovered.
04/25/2019 - Vulnerability reported to Advantech. 90-day date is July 24, 2019.
04/25/2019 - Advantech acknowledges receipt of the information. They will "check it."
04/30/2019 - Advantech states that they will "target a fix around 24 May for this issue."
04/30/2019 - Vulnerability 2 discovered.
05/08/2019 - Vulnerability disclosed to Advantech.
05/08/2019 - Advantech acknowledges receipt of the report and will have an engineer check it out.
05/09/2019 - Advantech will fix both bugs in the same release.
05/09/2019 - Advantech states that they will "expect to fix this in the next release around 24 May".
05/15/2019 - Advantech notifies us that the release will be postponed to May 31.
05/15/2019 - Tenable thanks Advantech for the update.
05/24/2019 - Tenable follows up to see if the bugs fixes are still on track for May 31.
05/26/2019 - Advantech is still targeting May 31, but it is "tight". Will confirm by Wednesday.
05/30/2019 - Advantech has to delay. They will try to release next week.
05/30/2019 - Tenable thanks Advantech for the update.
06/04/2019 - Tenable asks for an update.
06/04/2019 - Advantech pushes release date to June 12, 2019.
06/05/2019 - Tenable thanks Advantech for the update.
06/11/2019 - Tenable follows up to see if the release will go out tomorrow.
06/11/2019 - Advantech hopes to have a release out before the 14th.
06/11/2019 - Tenable thanks Advantech for the update. Informs Advantech of CVE IDs to be assigned.
06/14/2019 - Advantech says they will release 8.4.1 on Monday.
06/14/2019 - Tenable acknowledges.
06/18/2019 - Release notes are posted for 8.4.1. Tenable is unable to download the release notes or a trial installer. Asks Advantech if this version was officially released.
06/18/2019 - Advantech confirms that a patch was released.

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

Risk Information

Tenable Advisory ID: TRA-2019-28
CVSSv2 Base / Temporal Score:
10.0 / 7.8
CVSSv2 Vector:
(AV:N/AC:L/Au:N/C:C/I:C/A:C)
Affected Products:
Advantech WebAccess/SCADA 8.4.0
Risk Factor:
Critical

Advisory Timeline

06/18/2019 - Advisory released.
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