A remote code execution vulnerability exists when "Windows Theme API" does not properly decompress files.
An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the current user. If the current user is logged on with administrative user rights, an attacker could take control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
To exploit the vulnerability, a victim user must open a specially crafted file. In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and then convincing the user to open the file. In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) that contains a specially crafted file designed to exploit the vulnerability. An attacker would have no way to force a user to visit the website. Instead, an attacker would have to convince a user to click a link, typically by way of an enticement in an email or Instant Messenger message, and then convince the user to open the specially crafted file.
The security update addresses the vulnerability by helping to ensure that "Windows Theme API" properly decompresses files.