Flaw leaves Windows open to DOS attack, Microsoft warns

IDG News Service - A flaw in software code that implements a protocol for virtual private networks (VPN) makes Windows 2000 and Windows XP systems vulnerable to denial-of-service attacks, Microsoft Corp. warned late yesterday.
An unchecked buffer exists in the code that implements the Point-to-Point Tunneling Protocol (PPTP), which enables users to create and use VPNs and is natively supported by Windows 2000 and Windows XP, Microsoft said in a security bulletin. The software maker called the problem "critical."
PPTP is an option in routing and remote access services in server versions of Windows 2000 and Windows XP, and part of the remote access client in workstation versions. Systems are only at risk if PPTP has been enabled, Microsoft said.
Both server and client systems are at risk, though an attack on a client would be more difficult because it typically changes its IP address every time a connection is set up, Microsoft said. An attacker could cause a vulnerable system to fail by sending malformed PPTP control data to the system, Microsoft said.
A patch to fix the problem is available from Microsoft's TechNet Web site. Administrators offering PPTP services should install the patch immediately, and users of remote access using PPTP should consider installing it, Microsoft said.
Microsoft warned in a separate security bulletin yesterday of another "moderate" security issue affecting Windows 2000.
The default permission settings for the software provide users in the "Everyone" group full access to the system root folder. An attacker could mount a Trojan horse attack against users on the same system by placing a program in the root folder and having it run when another user signs on, Microsoft said. Administrators should consider changing access permissions on the Windows 2000 root directory, Microsoft said.