Tracking firm Secunia rated the flaws as "highly critical," saying successful exploitation could permit malicious code execution.
The bugs residing in the PowerPoint Viewer, used to display presentations, are caused by boundary errors in the viewer’s ActiveX control that can lead to stack-based buffer overflows, according a Secunia advisory. The flaws are located in the program, PowerPointViewer.ocx, and affect version 126.96.36.199.
OCX is the former name for ActiveX controls.
The other flaws impact Excel Viewer and are similarly caused by boundary errors in the Excel Viewer ActiveX control, specifically ExcelViewer.ocx, Secunia said in a separate advisory. If taken advantage of, the same result can occur. They are confirmed in version 188.8.131.52.
shinnai said today on the moAxB blog that "this component allow(s) you to visualize, create and modify XLS files."
"Some methods are unable to handle exceptional conditions, and this cause(s) the crash of the application that use(s) this component."
The hacker said on Milw0rm today that the exploit has been tested on Windows XP Professional with Service Pack 2 and Internet Explorer 7 installed.
Users are encouraged to set the kill-bit for the affected ActiveX controls, according to Secunia. The kill-bit feature prevents ActiveX execution in a user’s web browser.
Microsoft said it is monitoring the MoAxB project, another effort by the hacking community to expose a month's worth of vulnerabilities in a variety of computer components and applications.
"As always, the Microsoft Security Response Center(MSRC) will stand ready to mobilise its teams to investigate, fix and learn from any vulnerabilities discovered through the project, and the company will take appropriate action to protect its customers, as needed," a company spokesman told SCMagazine.com.
He added that Microsoft prefers when researchers report flaws directly to the vendor to "ensure that customers receive comprehensive, high-quality updates for security vulnerabilities without exposure to malicious attackers while the update is being developed."
Two Office flaws found in Month of ActiveX bugs
By Dan Kaplan on May 3, 2007 9:58AM
A hacker known as shinnai kicked off his "Month of ActiveX Bugs" (MoAxB) project with a bang by exposing a number of severe vulnerabilities affecting OCX controls in Microsoft Office.
Got a news tip for our journalists? Share it with us anonymously here.