One of the critical bulletins, MS04-023, titled "Vulnerability in HTML Help Could Allow Code Execution," addresses vulnerabilities in the Windows HTML Help system that were reported previously.
An attacker could execute code on the affected system and take complete control if that users privileges were sufficient, according to the bulletin. Updates are available for Windows NT4, Windows 2000, Windows XP and Windows Server 2003. No patch is available yet for Windows 9x, although the bulletin says one will be available later through Windows Update.
The other critical vulnerability, MS04-022, or "Vulnerability in Task Scheduler Could Allow Code Execution," also allows remote code execution. The affected component, which has an unchecked buffer, is installed in many recent versions of Windows, but not in Windows Server 2003.
Four bulletins are deemed "important," and Microsoft recommends that users install the updates "at the earliest opportunity."
MS04-024 appears to be the most significant. It appears to address the Windows shell API that has been the subject of many recent attacks. The bulletin lists as mitigating factors that the attacker would have to entice the user to visit a Web site with pages that incorporate the attack.
McAfee fellow Jimmy Kuo said McAfee Inc. rates this vulnerability more severely than Microsoft does, using an experimental in-house ratings system for vulnerabilities. The McAfee system takes into account the availability of proof of concept code in the wild, as is the case with the shell API vulnerability. Kuo said McAfee is not aware of any real-world attacks based on this vulnerability.
Another bulletin, MS04-019, describes a hole in the Utility Manager for Windows 2000 with Service Packs 2, 3 or 4. Utility Manager allows a user to start and stop accessibility programs such as the Magnifier, Narrator and On-Screen Keyboard. A privilege-escalation bug could allow a less-privileged user to run programs with system-level privileges.
MS04-020 describes a vulnerability in POSIX code handling in recent versions of Windows NT 4.0 and Windows 2000. Similar to the Utility Manager bug, this one could allow privilege escalation.
Only IIS 4.0 in Windows NT 4.0 is affected by another flaw, described in MS04-021. The vulnerability involves a buffer overrun in the IIS 4.0 redirect function that could allow the execution of arbitrary code.
Finally, MS04-018, termed a "moderate" problem, is a cumulative update for Outlook Express. The attack allows a denial of service by an attacker who uses a specially malformed e-mail header. A message with such a header could cause Outlook Express to fail.
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