New Win-NT, 2K, XP security holes

MS not worried - but maybe you should be

First up, the MUP (Multiple UNC Provider) in Windows NT, 2K and XP contains an unchecked buffer which can be exploited to escalate user privileges, making it possible for an attacker to run arbitrary code at the OS level.

UNC refers to the Universal Naming Convention, with which shares are identified. MUP is a Windows service which locates UNC resources. In this case, MUP file requests are stored in two buffers. The first is checked properly, but "MUP stores a second copy of the file request when it sends this request to a redirector," MS says. The second buffer is not adequately checked, and is therefore susceptible to a buffer overflow attack.

MS calls this one moderate, because the attacker has to log on to the system as a user, and has to be able to copy a file that calls MUP in a tricky way. In other words, the user has to log on interactively.

"If normal security restrictions are observed, unprivileged users will not be able to log onto critical machines such as domain controllers, and as a result would be unable to attack them," MS hastens to point out.

Thus workstations and terminal servers are the systems most at risk, MS says. Also, the Win-2K kernel handles the second buffer and is not externally controllable, so it may be impossible to own the machine, but merely crash it.

As for it being 'moderate,' I don't know. Any vulnerability which can crash or give up control of a critical system sounds pretty serious to me. Unfortunately, the MS bulletin is characteristically light on exploitation details, so we're in no position to take issue. We'll point out that the evil ingenuity of the blackhat development community is not something to underestimate. Since we don't know clearly how an exploit would work, we don't know how difficult it would be to overcome the obstacles MS cites.

Affected systems are: NT 4 Workstation; NT 4 Server; NT 4 Server Enterprise Edition; NT 4 Terminal Server Edition; 2K Pro; 2K Server; 2K Advanced Server; and XP Pro. Patches are available for download here.



Next up, we have a nifty way for an attacker to deny the application of Group Policy in Win-2K through the use of an exclusive read session, which blocks access to the relevant files.

According to MS, "an attacker would likely exploit the vulnerability by first logging onto the domain normally, and then opening the Group Policy files with exclusive read access. She* could then log onto the network a second time. Because the policy files would be locked, the second logon would occur without Group Policy being applied. The result would be that, although all previous Group Policy settings on the second machine would remain in force, any new policy settings would not be applied. The attacker's second session would take place using what policy settings had most recently been applied."

From this doublespeak we may take away two useful nuggets. If the attacker logs in through a machine with Group Policy in force, the pre-existing policies will remain in effect. However, if the attacker connects through a machine which has never had Group Policy defined, well, MS' default settings would be in force. (Machine owned? You be the judge. MS refuses to say one way or the other.)

If users are permitted to log onto the domain via the Internet, then there is obvious potential for remote exploitation. However, the vulnerability does not yield write access to the relevant files. Policy can be blocked, not re-written.

Other users can benefit from the attack, but only if they're informed. "The attacker would know that [Group Policy] hadn't been applied, because she* would know that she* had locked the files. But other users wouldn't have any indication that Group Policy had been blocked."

MS points out that an attacker's login and password will be logged, so admins should be able to catch anyone trying this so long as they're using their own credentials. Smart attackers don't, however, so look into this carefully before accusing anyone of mucking about with the equipment.

Affected systems are: 2K Server; 2K Advanced Server; and 2K Datacenter Server. Patches may be downloaded here.

* --All right, I'm only going to say this once: 'He' is the singular indefinite pronoun in English ("if a person drinks too much, he will likely experience a hangover"). 'He' also happens to be the masculine personal pronoun.

'She' is the singular pronoun of personification in English ("if England fails to advance America's foreign-policy ambitions, she will suffer terrible consequences"). 'She' also happens to be the feminine personal pronoun.

Confusing the two exhibits not a warm-and-fuzzy concern for the inclusion of women so much as a writer's or speaker's ignorance. Using the feminine personal pronoun as an indefinite article is as moronic as using the masculine personal pronoun for personification. Thus the captain greets us: "Welcome to my ship. Isn't he splendid?"

Give it up, people. It's not thoughtful; it's just illiterate. ®

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