The main class of vulnerability that is detected and patched on Internet Explorer 8 for Windows server include is Remote Code Execution
As of this writing the latest patch came out on Feb 8, 2011 that contained fixes for the a number of issues. Some of these include:
CSS Memory Corruption Vulnerability.
Per CVE-2010-3971 this issue came up because of a vulnerability in the CSharedStyleSheet::Notify function in the Cascading Style Sheets (CSS) parser in mshtml.dll, that is used in Microsoft Internet Explorer 6 through 8 and other products. This vulnerability allows remote attackers to execute arbitrary code or cause a denial of service (application crash) via a self-referential @import rule in a style sheet.
Uninitialized Memory Corruption Vulnerability.
Per CVE-2011-0035 Microsoft Internet Explorer 8 does not properly handle objects in memory, which allows remote attackers to execute arbitrary code by accessing an object that (1) was not properly initialized or (2) is deleted, leading to memory corruption.
Almost all the issues reported lead to remote code execution that if successfully exploited could gain the same user rights as the logged-on user. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.