Microsoft warned of a critical security flaw Wednesday that affects all supported versions of its Windows operating system and could enable a remote attacker to run malicious code on unpatched Windows systems.
The security hole is due to a buffer overrun vulnerability in the Windows HTML converter, a Windows component that enables Windows to convert files from Rich Text Format (RTF) to HTML (HyperText Markup Language), which is used to display documents on the Web.
The flaw exists in an HTML converter feature used to handle content that is cut and pasted within Windows. When properly exploited, the flaw could cause the converter to crash, enabling an attacker to deposit and run his or her own code on the affected system, Microsoft said.
Because the converter is also used by the Internet Explorer Web browser, malicious hackers could launch attacks by sending specially crafted email messages to vulnerable systems or tricking users into visiting Web pages designed to exploit the vulnerability.
Once a user visited such a site or opened an email, no further user interaction would be required to cause the buffer overrun, Microsoft said.
Privilege level While the vulnerability was rated critical for most versions of the Windows operating system, the company noted that attackers who successfully exploited the vulnerability would only gain the privilege level of the current user. For non-administrative users, that could limit the damage caused on exploited systems, Microsoft said.
In addition to its Security Bulletin, MS03-023, Microsoft issued patches for all affected systems up to and including the most recent Windows Server 2003 release.
Microsoft encouraged all affected customers to apply the appropriate patch at the earliest possible opportunity.
In addition to the HTML converter vulnerability, Microsoft issued patches for two other software flaws Wednesday, MS03-024 and MS03-025, both rated "Important" by the company.
Bulletin MS03-024 concerns a buffer overrun problem affecting the Server Message Block protocol on machines running Windows NT 4.0, 2000 and XP Professional. That problem, if left unpatched, could lead to the corruption of data stored on the system and enable an attacker to execute malicious code.
Bulletin MS03-025 concerns a flaw in Windows Utility Manager on systems running Windows 2000.
The Utility manager is used to monitor the status of some of Microsoft's accessibility options for persons with disabilities. The vulnerability could enable a malicious user to perform actions on the system in excess of his or her privilege level, Microsoft said.