Express Compressed Fonts Remote Code Execution Vulnerability

A remote code execution vulnerability exists when the Windows font library improperly handles specially crafted embedded fonts. An attacker who successfully exploits exploited this vulnerability would gain code execution on the target system. 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.

There are multiple ways an attacker could exploit the vulnerability:

• In a web-based attack scenario, an attacker could host a specially crafted website that is designed to exploit the vulnerability and then convince users to view the website. An attacker would have no way to force users to view the attacker-controlled content. Instead, an attacker would have to convince users to take action, typically by getting them to click a link in an email or Instant Messenger message that takes users to the attacker’s website, or by opening an attachment sent through email.
• In a file sharing attack scenario, an attacker could provide a specially crafted document file that is designed to exploit the vulnerability, and then convince users to open the document file.

The security update addresses the vulnerability by correcting how the Windows font library handles embedded fonts.