IOServer Directory Traversal / File Download

Type packetstorm
Reporter hinge
Modified 2012-08-18T00:00:00


BEGIN Security Advisory: foofus-20120817 BEGIN  
Title: IOServer "Root Directory" Trailing Backslash Web Server Vuln  
Allows: Arbitrary File Access, Directory Listing, Directory Traversal  
CVSS Base / Temporal / Overall Scores: 7.8 / 6.4 / 6.4  
Advisory Version: 2 (first publicly released version is 2)  
Advisory Release Date: 2012-08-17  
Advisory Last Updated: 2012-08-17  
Vendor: IOServer Pty Ltd.  
Affected Product: IOServer (and earlier?)  
Issue Status: fixed version and workarounds available  
1. Summary  
== =======  
IOServer is a piece of industrial control software that runs on Windows.  
It contains a built-in web server to support the "XML Server" feature.  
This web server can be abused to download any file on the file system  
without authentication, if the "Root Directory" setting does not contain  
a trailing backslash. Note that a sample configuration provided with the  
product exhibits a vulnerable configuration.  
2. Description  
== ===========  
The vendor's web site describes IOServer thusly:  
"OPC (OLE for Process Control) Server for Windows NT 4.0 / 95 / 98 /  
ME / 2000 / 2003 / XP / 2008 / 7. Interface to multiple protocols  
through a single OPC Server. This software allows OPC clients such as  
HMI (Human Machine Interface) and SCADA (Supervisory Control and Data  
Acquisition) systems to exchange plant floor data with PLC (Programmable  
Logic Controllers)."  
If the "XML Server" feature is turned on (apparently by configuring a  
valid "Root Directory" on the "XML Server" tab), the integrated web  
server listens on the configured port (81 by default). If the "Root  
Directory" configuration value does not contain a trailing backslash,  
then these issues exist.  
A directory traversal vulnerability exists such that the web server can  
be tricked to serve up any file on the server, outside of the configured  
"Root Directory". On Windows, one common thing to do with an issue like  
this is to download the backup copy of the SAM, in order to retrieve  
password hashes and mount an offline attack on them. Any other  
potentially sensitive file on the server can be accessed this way as  
well, if the attacker knows the path to it.  
Note that directory traversal is only needed if you want to break out of  
the "Root Directory". The web server will serve up files inside the  
"Root Directory" just by asking it for them. This may or may not be  
considered a vulnerability, depending on the expectations of the  
Also, the web server allows directory listings in some cases, whether  
inside or outside the "Root Directory". Again, this may or may not be  
considered a vulnerability depending on expectations.  
Note also that the "XML Server Settings" tab contains fields for a "Read  
Password" and "Write Password", which are apparently intended to only  
restrict access to the devices via the XML web interface (they are not  
intended to restrict access to other content served by the web server).  
By default, they are set to blank. But due to their intended use of  
resticting device access, they do nothing to stop access to the file  
system as described here even if they are set to some value.  
3. Proof of Concept / Steps to Reproduce  
== ===== == ======= = ===== == =========  
Install the software and use the sample Modbus Web Server configuration  
from to get it working. This sample  
configuration uses the "Root Directory" value of "C:\Program Files  
\IOServer\Docs" (note the lack of a trailing backslash). This directory  
does not exist unless you install the documentation package (isodoc.exe,  
available from the vendor web site). You can get to a vulnerable  
configuration if you leave the "Root Directory" alone and install the  
documentation package, or just modify the "Root "Directory" value to  
something valid (but lacking a trailing backslash) like "C:\Program  
Files\IOServer". Note that the software or server may need to be  
restarted, then you will see a web server listening on the configured  
port (81 by default).  
Note that more recent versions of the software default to "C:\IOServer"  
rather than "C:\Program Files\IOServer". This does not affect the issues  
discussed here.  
To request files within the "Root Directory", just ask for them with a  
browser or command-line tool like wget:  
wget http://target-server:81/modbus.dll  
To get a directory listing, just ask:  
wget http://target-server:81/  
To request files outside of the "Root Directory", use a standard  
directory traversal trick with a client or browser that supports it.  
Note that IE probably will not allow this type of malfeasance:  
wget http://target-server:81/.../.../.../windows/repair/sam  
To get a directory listing outside of the "Root Directory", ask for it  
with the directory traversal trick:  
wget http://target-server:81/.../.../.../windows/  
Note that it is only this directory traversal issue that was fixed in  
version Accessing files and directory listings inside the  
"Root Directory" is apparently intended operation.  
4. Impact  
== ======  
Unexpected arbitrary access to the file system can lead to the  
disclosure of sensitive information. Worst case, disclosure of the  
system's password hashes can lead to compromise of the passwords, and  
therefore, of the server.  
5. CVSS Scoring  
== ==== =======  
CVSS Base Score: 7.8  
Impact Subscore: 6.9  
Exploitability Subscore: 10  
CVSS Temporal Score: 6.4  
Overall CVSS Score: 6.4  
Access Vector: Network  
Access Complexity: Low  
Authentication: None  
Confidentiality Impact: Complete  
Integrity Impact: None  
Availability Impact: None  
Exploitability: Functional exploit exists  
Remediation Level: Official fix  
Report Confidence: Confirmed  
Note that the CVSS calculation was based only on the directory traversal  
issue, since it is the most obvious and serious vulnerability addressed  
6. Affected Products  
== ======== ========  
IOServer (earlier versions are also assumed vulnerable)  
This was downloaded from, which was  
the current version as of 23 April 2012. Older versions were not  
available, but are assumed vulnerable.  
(you can check your version in the IOServer GUI using Help, About  
7. Workarounds / Solutions  
== =========== = =========  
Ensure that the "Root Directory" value has a trailing backslash. This  
eliminates most of the issues, although you can still get a directory  
listing of the "Root Directory" itself (but not subdirs) even with this  
in place.  
Of course, limit access to the web server port to only trusted  
hosts/networks. Even a fixed version should probably not be exposed to  
the Internet or other untrusted networks.  
The directory traversal issue was fixed in version  
(, released on 2012-06-20. However,  
arbitrary file access and directory listings inside the "Root Directory"  
and its subdirs are still possible in this version, unless the trailing  
backslash is in place. Note that even with the trailing backslash,  
directory listing of the "Root Directory" itself is still possible.  
It is recommended that all three of the above actions (use the trailing  
backslash, limit access to trusted networks/hosts only, and upgrade to or later) be taken in order to secure this web server as much  
as possible.  
8. Timeline  
== ========  
2012-04-23: First vendor contact  
2012-04-23: Vendor sends proposed fix (that was fast!)  
2012-04-27: Proposed fix found incomplete, feedback to vendor  
2012-05-04: Vendor sends second proposed fix  
2012-05-17: Verified that second proposed fix resolves all known  
directory traversal issues  
2012-05-17: Vendor informs that directory listing and arbitrary file  
access issues inside the Root Directory are intended functionality  
2012-05-18: This issue put on the back burner due to urgent project; I  
then completely forget about it (oops, my bad)  
2012-06-20: Vendor releases fixed version (, aka "driver19.exe")  
2012-08-08: I remember about this; recheck all information and retest  
current version; edits to advisory; contact vendor about public  
release date  
2012-08-17: Public release  
9. Credit  
== ======  
Well, actually, this vulnerability was found by Nessus, plugin ID 10297  
(which looks for generic web server directory traversal issues, not  
specific to IOServer of course). All I did was see it in the scan  
results, verify it, reproduce it for testing, report it to the vendor  
and write this advisory.  
Thanks to my friends at, and to IOServer for being very  
responsive and open.  
END Security Advisory: foofus-20120817 END