Security Watch

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Buffer Overflow in Windows Locator Service
A buffer overflow in the Windows Locator service may make it possible for a remote attacker to execute arbitrary code on a vulnerable system by sending an overly large request to the Windows Locator service.

Microsoft describes the Windows Locator service as "a name service that maps logical names to network-specific names."

A client that is going to make a Remote Procedure Call (RPC) can call the Locator service to resolve a logical name for a network object to a network-specific name for use in the RPC. For example, if a print server has the logical name "laserprinter", an RPC client could call the Locator service to find out the network-specific name that mapped to "laserprinter". The RPC client uses the network-specific name when it makes the RPC call to the service.

This service is enabled and running by default on Windows 2000 domain controllers and Windows NT 4.0 domain controllers.

Impact
A remote attacker may be able to execute arbitrary code on a vulnerable system, or cause the Windows Locator service to fail. An attacker who is able to compromise a domain controller might be able to cause the compromised domain controller to trust the attacker's domain.

Systems Affected
Microsoft Windows NT 4.0, Windows NT 4.0, Terminal Server Edition, Windows 2000, Windows XP

Solution/Patches
Microsoft has provided the following information to assist in downloading the appropriate patch for your platform(s):
Windows NT 4.0, Windows NT 4.0 Terminal Server Edition, Windows 2000, Windows XP:

• 32-bit Edition
• 64-bit Edition

Disable vulnerable service
Until a patch can be applied, you may wish to disable the Windows Locator service. To determine if the Windows Locator service is running, check the following:

The status of the 'Remote Procedure Call (RPC) Locator' service and how it is started (automatically or manually) can be viewed in the Control Panel. For Windows 2000 and Windows XP, use Control Panel | Administrative Tools | Services, and on Windows NT 4.0, use Control Panel | Services.

It is also possible to determine the status of the Locator service from the command line by entering: net start

A list of services will be displayed. If 'Remote Procedure Call (RPC) Locator' appears in the list, then the locator service is running.

To disable the Windows Locator service:

An administrator can disable the Locator service by setting the RpcLocator service status to "disabled" in the services control panel.

The service can also be stopped via the command line using the sc.exe program, which ships with Windows XP and is included as part of the Windows 2000

Resource Kit. The following command will stop the service: sc stop RpcLocator

To disable the service using the command line tool, use the following: sc config RpcLocator start= disabled

Restrict access to NetBIOS
You may want to block access to NetBIOS from outside your network perimeter, specifically by blocking access to ports 139/TCP and 445/TCP. This will limit your exposure to attacks. However, blocking at the network perimeter would still allow attackers within the perimeter of your network to exploit the vulnerability. It is important to understand your network's configuration and service requirements before deciding what changes are appropriate.

As a best practice, it is recommended to disable all services that are not explicitly required. Before deciding to disable the Windows Locator service, carefully consider your service requirements.

Please also note that Microsoft is actively deploying the patches for this vulnerability via Windows Update.

Vendor Information
Microsoft Corporation
www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/ms03-001.asp

Buffer Overflows in ISC DHCPD Minires Library
The Internet Software Consortium (ISC) has discovered several buffer overflow vulnerabilities in their implementation of DHCP (ISC DHCPD). These vulnerabilities may allow remote attackers to execute arbitrary code on affected systems.

The Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuration information to hosts on a TCP/IP network. In addition to supplying hosts with network configuration data, ISC DHCPD allows the DHCP server to dynamically update a DNS server, eliminating the need for manual updates to the name server configuration. Support for dynamic DNS updates is provided by the NSUPDATE feature.

During an internal source code audit, developers from the ISC discovered several vulnerabilities in the error handling routines of the minires library, which is used by NSUPDATE to resolve hostnames. These vulnerabilities are stack-based buffer overflows that may be exploitable by sending a DHCP message containing a large hostname value.

Note: Although the minires library is derived from the BIND 8 resolver library, these vulnerabilities do not affect any current versions of BIND.

Impact
Remote attackers may be able to execute arbitrary code with the privileges of the user running ISC DHCPD.

Systems Affected
Systems running ISC DHCPD versions 3.0 through 3.0.1RC10, inclusive.

Solution
The ISC has addressed these vulnerabilities in versions 3.0pl2 and 3.0.1RC11 of ISC DHCPD.

Disable dynamic DNS updates (NSUPDATE)
As an interim measure, the ISC recommends disabling the NSUPDATE feature on affected DHCP servers.

Block external access to DHCP server ports
It is possible to limit exposure to these vulnerabilities by restricting external access to affected DHCP servers on the following ports:

• bootps 67/tcp # Bootstrap Protocol Server
• bootps 67/udp # Bootstrap Protocol Server
• bootpc 68/tcp # Bootstrap Protocol Client
• bootpc 68/udp # Bootstrap Protocol Client

Disable the DHCP service
As a general rule, it is recommended disabling any service or capability that is not explicitly required. Depending on your network configuration, you may not need to use DHCP.

Vendor Information
Debian
Debian has updated their distribution with DSA 231.

For the stable distribution (woody) this problem has been fixed in version 3.0+3.0.1rc9-2.1.

The old stable distribution (potato) does not contain dhcp3 packages.

For the unstable distribution (sid) this problem has been fixed in version 3.0+3.0.1rc11-1.

Internet Software Consortium
They have a patched version of 3.0 available (3.0pl2) and a new release candidate for the next bug-fix release (3.0.1RC11). Both of these new releases are available from www.isc.org/products/DHCP/.

Red Hat Inc.
Red Hat distributes a vulnerable version of ISC DHCP in Red Hat Linux 8.0. Other distributions of Red Hat Linux are not vulnerable to these issues. New DHCP packages are available along with an advisory at the URL below. Users of the Red Hat Network can update their systems using the 'up2date' tool.

http://rhn.redhat.com/errata/RHSA-2003-011.html