CVE-2017-2867
An exploitable code execution vulnerability exists in the SavePatientMontage functionality of Natus Xltek NeuroWorks 8. A specially crafted network packet can cause a stack buffer overflow resulting in code execution. An attacker can a malicious packet to trigger this vulnerability.
Natus Xltek NeuroWorks 8
http://www.natus.com/index.cfm?page=products_1&crid=224
9.0 - CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CWE-121: Stack-based Buffer Overflow
Natus NeuroWorks 8 provides a networking solution for the Natus Xltek EEG products. In particular, it is used to monitor and review study data from anywhere on the network. This advisory looks into the NWStorage service bundled with NeuroWorks.
The modules used in this advisory are shown below:
0:006> lm vm Storage
start end module name
00400000 00471000 storage (deferred)
Image path: c:\Neuroworks\storage.exe
Image name: storage.exe
Timestamp: Wed Nov 06 10:11:09 2013 (527A863D)
CheckSum: 0006EC3D
ImageSize: 00071000
File version: 8.0.1.1544
Product version: 8.0.1.1544
One of the key data structures in Neuroworks is the KeyTree. Internally, a KeyTree is a List of Lists. The List and KeyTree structs are shown below:
KeyTree/List
char opcode; // 5 for KeyTree, 4 for ItemList
int num_elements ; // Number of elements in this KeyTree
Item[num_elements] items; // List of elements
During the processing of the SavePatientMontage
command, a client supplied KeyTree is parsed looking for a Data.Name
key. The extraction of the Data.Name
element is shown below:
.text:00410E2D 12C push offset str.unknown
.text:00410E32 126 lea this, [esp+130h+sNewName]
.text:00410E36 130 push this
.text:00410E37 134 push offset str.Data_Name ; "Data.Name"
.text:00410E3C 138 mov this, edi ; Client supplied KeyTree
.text:00410E3E 138 call esi ; CKeyTree::GetAt(char const *)
This return value is an Item type. In order to extract the literal string from the Item, CItem::AsCStr
is called as shown below:
.text:00410E40 12C mov this, eax
.text:00410E42 12C call ds:CItem::AsCStr(char const *)
This string is finally passed to makepath
in order to create a file path in preparation for setting a local variable.
.text:00410E6A 134 push eax ; Client controlled string
.text:00410E6B 138 lea edx, [esp+138h+path]
.text:00407E6F 138 push 0
.text:00407E71 13C push edx
.text:00407E72 140 call ds:__imp___makepath
Makepath
does not guarantee that the resulting string will fit in the supplied buffer. The client can supply a string larger than the allocated stack buffer, causing a buffer overflow. Due to the overflow, the exception handlers have been overwritten giving direct control of the program.
Attacker controlled stack canary value in `ecx`:
eax=7883af50 ebx=00000000 ecx=deadbeef edx=00000084 esi=230046d0 edi=04ec99a0
eip=00410f02 esp=0012f97c ebp=1abaefe0 iopl=0 nv up ei pl nz na pe nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000206
storage!CPatientDoc::UpdatePatientMontageFileName+0x142:
00410f02 33cc xor ecx,esp
2017-07-15 - Initial Contact
2017 -10-06 - Vendor Acknowledged
2018-04-04 - Public Release
Discovered by Cory Duplantis and Tyler Bohan of Cisco Talos.