The Universal Plug and Play (UPnP) service allows computers to discover and use network-based devices. Windows ME and XP include native UPnP services; Windows 98 and 98SE do not include a native UPnP service, but one can be installed via the Internet Connection Sharing client that ships with Windows XP. This bulletin discusses two vulnerabilities affecting these UPnP implementations. Although the vulnerabilities are unrelated, both involve how UPnP-capable computers handle the discovery of new devices on the network.

The first vulnerability is a buffer overrun vulnerability. There is an unchecked buffer in one of the components that handle NOTIFY directives – messages that advertise the availability of UPnP-capable devices on the network. By sending a specially malformed NOTIFY directive, it would be possible for an attacker to cause code to run in the context of the UPnP service, which runs with System privileges on Windows XP. (On Windows 98 and Windows ME, all code executes as part of the operating system). This would enable the attacker to gain complete control over the system.

The second vulnerability results because the UPnP doesn’t sufficiently limit the steps to which the UPnP service will go to obtain information on using a newly discovered device. Within the NOTIFY directive that a new UPnP device sends is information telling interested computers where to obtain its device description, which lists the services the device offers and instructions for using them. By design, the device description may reside on a third-party server rather than on the device itself. However, the UPnP implementations don’t adequately regulate how it performs this operation, and this gives rise to two different denial of service scenarios.

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