Vulnerability Note VU#361684

The UPnP protocol allows automatic device discovery and interaction with devices on a network. The UPnP protocol was originally designed with the threat model of being on a private network (not available to the WAN) restricted to only authorized users, and therefore does not by default implement authentication. Later efforts developed a UPnP Security standard, but according to UPnP Forum's Device Protection standard documentation, "support and deployment of this standard has been extremely limited", due to cumbersome user experience and lack of industry buy-in of advanced features such as Public Key Infrastructure (PKI).

According to the reporter, poor adoption of the security standard may broadly open up opportunities for an attacker with private network access to guess the UPnP Control URLs for many devices currently on the market. If the guess is correct, the attacker may utilize UPnP to make changes to the home router's configuration such as opening ports and enabling services that allow an attacker further access to the network. A correct guess is likely, due to many manufacturers' use of standardized UPnP Control URL names.

Some vendors have reported that their devices randomize the UUID in the Control URL, making guessing the correct URL much more difficult, but many vendors have not taken this action. For more information, see the Vendor Information section below. It is currently unclear how widespread the deployment of UPnP security standards is in these devices.

One possible method of gaining enough access to the private network to utilize UPnP is through a DNS Rebinding attack, which is well-known in the security community. Previously, it has been reported that Flash may be utilized to gain control of UPnP.

The reporter has more information on this issue at http://www.filet-o-firewall.com.

An attacker able to gain access to the private network by enticing a user to visit a specially-crafted web page may be able to silently open ports in a user's firewall or perform other administrative actions on the gateway router.

The CERT/CC is currently unaware of a full solution to this problem. However, the following workarounds may help mitigate risks.

Do not follow unknown links

Exercise caution when following links to URLs you do not recognize.

Disable UPnP

Consider disabling UPnP services on your home network. Some users may require UPnP services on their network; if so, users must exercise judgment and weigh risks versus rewards of operating such a network. When purchasing networking equipment, consider devices that have implemented the latest UPnP standards and security.

Furthermore, if you are a developer or manufacturer of devices using UPnP, consider the following:

Randomize the UUID in the control URL

Randomizing appropriate UPnP UUIDs and URLs may help mitigate brute force attacks, but likely is not a full solution.

Implement latest UPnP standards

Consider implementing the latest UPnP standards such as Device Protection in order to provide better security to devices utilizing UPnP.