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UPNP - Multiple Remote Windows XP/ME/98 Vulnerabilities

Release Date: December 20, 2001
Severity: High
Vendor: Microsoft

Systems Affected:
Microsoft Windows XP (All default systems)
Microsoft Windows 98 (Certain configurations)
Microsoft Windows 98SE (Certain configurations)
Microsoft Windows ME (Certain configurations)

Windows XP ships by default with a UPNP (Universal Plug and Play) service which can be used to detect and integrate with UPNP aware devices. Windows ME does not ship by default with the UPNP service; however, some OEM versions do provide the UPNP service by default. Also, it is possible to install the Windows XP Internet Connection Sharing on top of Windows 98, therefore making it vulnerable.

As described on upnp.org: "UPNP architecture offers pervasive peer-to-peer network connectivity of PCs of all form factors, intelligent appliances, and wireless devices. UPNP architecture leverages TCP/IP and the Web to enable seamless proximity networking in addition to control and data transfer among networked devices in the home, office, and everywhere in between".

Technical Details:
We at eEye believe that there are several security issues with the UPNP protocol itself; however, these more generic issues are out of the scope of this advisory. Expect a detailed paper to be released from eEye within the coming weeks.

This advisory covers three vulnerabilities within Microsoft's UPNP implementation.
A remotely exploitable buffer overflow to gain SYSTEM level access to any default installation of Windows XP, a Denial-of-Service (DoS) attack, and a Distributed Denial-of-Service (DDoS) attack.

1. The SYSTEM Remote Exploit
The first vulnerability within Microsoft's implementation of the UPNP protocol can result in an attacker gaining remote SYSTEM level access to any default installation of Windows XP. SYSTEM is the highest level of access within Windows XP.

During testing of the UPNP service, we discovered that by sending malformed advertisements at various speeds we could cause access violations on the target machine. Most of these violations were due to pointers being overwritten. The following describes one instance of our testing:

Example Session:
CACHE-CONTROL: max-age=10
NT: urn:schemas-upnp-org:device:InternetGatewayDevice:1
NTS: ssdp:alive
SERVER: EEYE/2001 UPnP/1.0 product/1.1
USN: uuid:EEYE

If a buffer is incremented in the protocol, port, and uri fields of the Location URL and send sessions with 10,000 microsecond intervals, access violations will begin to be observed. In one situation, The EAX and ECX registers will contain addresses that are pulled from the memory that was overwritten and the svchost.exe process will access an invalid memory address at a "mov" instruction. It throws an access violation due to the fact that the destination address is an overwritten pointer, but there is nothing interesting at 0x41414141.

During our testing we discovered that there are multiple points of exploitation. We found instances of stack overflows and heap overflows, both of which were exploitable. In the case of the heap overflow we saw pointers being overwritten for both buffers and functions.

The SSDP service also listens on Multicast and Broadcast addresses. Therefore gaining SYSTEM access to an entire network of XP machines is possible with only one anonymous UDP SSDP attack session.

2. The DoS and DDoS
UPNP consists of multiple protocols, one of which being the Simple Service Discovery Protocol (SSDP). When a UPNP enabled device is installed on a network, whether it be a computer, network device, or even a household appliance, the device sends out an advertisement to notify control points of its existence. On a default XP installation, no support is added for device control as it would be the case in an installation of UPNP from "Network Services".

Although Microsoft added default support for an "InternetGatewayDevice", if an application is set up to "sniff" a network with XP, XP can be observed searching for this device as XP is loading. This support was added to aid leading network hardware manufactures in making UPnP enabled "gateway devices".

By sending a malicious spoofed UDP packet containing an SSDP advertisement, an attacker can force the XP/ME client to connect back to a specified IP address and pass on a specified HTTP/HTTPS request.

An example session:
CACHE-CONTROL: max-age=1
NT: urn: schemas-upnp-org:device:InternetGatewayDevice:1
NTS: ssdp:alive
USN: uuid:EEYE

The above packet data needs to be sent as a UDP packet to port 1900 of the XP/ME machine.

When the XP machine receives this request, it will interpret the URL following the LOCATION header entity. With no sanitizing of the URL it is passed on to the functions in the Windows Internet Services API. The string is broken down and the new session is created.

For example:
LOCATION: http://xptest.example.com:19/himom.html

A malicious attacker could specify a chargen service on a remote machine causing the XP client to connect and get caught in a tight read/malloc loop. Doing this will throw the machine into an unstable state where CPU utilization is at %100 and memory is being allocated to the point that it is totally consumed. This basically makes the remote XP system completely unusable and requires a physical power-off shutdown.

Attackers could also use this exploit to control other XP machines, forcing such machines to perform Unicode attacks, double decode, or random CGI exploiting. Due to the insecure nature of UDP, an attacker can exploit security holes on a web server using UPNP with almost total anonymity.

One of the bigger problems, and why this can become a DDoS attack, is that this SSDP announcement can be sent to broadcast addresses and multicast. It is therefore possible to send one UDP packet causing all XP machines on the target network to be navigated to the URL of choice, performing an attack of choice.

Also since parts of the UPNP service are implemented as UDP (in our opinion, a bad idea), it makes all of these attacks completely untraceable.

Vendor Status:
Microsoft has released a patch and security bulletin which is located at:

To verify that the patch has been installed on your system, do the following:
Windows 98 and 98SE:
Select Start, then Run, then run the QFECheck utility. If the patch is installed, "Windows 98 Q314941 Update" will be listed among the installed patches. To verify the individual files, use the file manifest provided in Knowledge Base article Q314941.

Windows ME:
Select Start, then Run, then run the QFECheck utility. If the patch is installed, "Windows Millennium Edition Q314757 Update" will be listed among the installed patches. To verify the individual files, use the file manifest provided in Knowledge Base article Q314757.

Windows XP:
Confirm that the following registry key has been created on the machine: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows XP\SP1\Q315000. To verify the individual files, use the date/time and version information provided in the following registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows XP\SP1\Q315000\Filelist.

The Common Vulnerabilities and Exposures (CVE) project has assigned the following two IDs:
The Buffer Overflow: CAN-2001-0876
The Denial of Service: CAN-2001-0877
This is a candidate for inclusion in the CVE list http://cve.mitre.org) which standardizes names for security problems.

We would strongly suggest denying all UPNP traffic at your internet borders as there is really no need to allow UPNP traffic across the Internet. Also, it would be wise to completely turn off the UPNP services as most users are probably not utilizing them. The less services running on your machine, the safer you will be. The SSDP Discovery Service and Universal Plug and Play Host service should both be set to disabled.

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