The company acknowledged the vulnerability last week. It is also planning to fix a second "browse-and-get-owned" vulnerability in its DirectShow software that was disclosed in May.
Both of these flaws affect older version of Windows; Windows Vista and Windows Server 2008 are not affected.
'[O]ur engineering teams have been working around the clock to produce an update for [the Microsoft Video ActiveX Control vulnerability] and we believe that they will be able to release an update of appropriate quality for broad distribution that protects against the attacks we detailed in the advisory," said Jerry Bryant, senior security program manager at Microsoft, in a blog post on Thursday.
Microsoft said in an advanced summary of its upcoming July 14 security patch that it plans to release six security bulletins.
Three will be "critical" updates for Windows, one of which affects Windows Vista and Windows Server 2008. There will also be one "important" update for Publisher, one "important" update for Internet Security and Acceleration (ISA) Server, and one "important" update for Virtual PC and Virtual Server.
Security vendors Trend Micro and Websense have noted that the ActiveX flaw is being actively exploited on Web sites in China.
"Around 967 Chinese Web sites are reported to be infected by a malicious script that leads users to successive site redirections and lands them to download a .JPG file containing the exploit," said Trend Micro security engineer Roland Dela Paz in a blog post.
And Bryant said that Microsoft is aware of limited attempts to exploit the DirectShow vulnerability.