Microsoft pushed out eight security bulletins as part of this month's Patch Tuesday, including a fix for a vulnerability currently under attack.
According to the advisory, hackers have begun launching limited, targeted attacks against a vulnerability in an ActiveX control for the Microsoft Visual Basic 6.0 Runtime Extended Files. Visual Basic 6.0 Runtime Extended Files include select ActiveX controls, libraries and tools delivered with the Visual Basic 6.0 Integrated Development Environment (IDE) media and as an online release. The files are typically installed either by Visual Basic 6.0 IDE or Microsoft.com.
According to Microsoft, hackers have painted a bull's-eye on a memory corruption issue involving the Masked Edit ActiveX Control. In that case, the ActiveX control fails to handle property values correctly, causing a buffer overrun when used in Internet Explorer that could allow an attacker to run arbitrary code and take over a vulnerable system.
As a workaround, organizations can follow the directions provided by Microsoft to disable the ActiveX Control in Internet Explorer.
The Masked Edit issue is just one of six affecting Visual Basic 6.0 Runtime Extended Files. The rest of the bulletin covers memory corruption issues involving the Charts, DataGrid, FlexGrid and Hierarchical FlexGrid ActiveX controls. Also addressed is an allocation error involving the Windows Common ActiveX control that occurs when parsing a specially crafted AVI file.
All totaled, six of the eight bulletins-including the one dealing with Visual Basic-are classified by Microsoft as "critical." The other critical bulletins cover remote code execution issues in Microsoft Excel, Internet Explorer, Word, Outlook and Windows.
The Excel bulletin covers three bugs, including two file format parsing vulnerabilities Microsoft considers likely to see consistent exploit code. Among the critical bulletins, Microsoft also declared one of the eight vulnerabilities affecting Word and Outlook and three of the four affecting Internet Explorer to be likely candidates for consistent exploit code.
The Word and Outlook bugs are rated "critical" for Word 2000 and Outlook 2007, but "important" for other versions. The IE vulnerabilities affect multiple versions, including 7.0, across several operating systems.
The two critical Windows bulletins address flaws in the Windows GDI (graphics device interface) and Windows Search. The GDI bulletin deals with two bugs, both of which can be exploited via a specially crafted WMF image file. The first is the result of an integer overflow situation that occurs when GDI improperly processes a malformed header in a WMF image file. The second issue is due to a heap overflow vulnerability caused by the way GDI handles file size parameters in WMF files.
There are also two bugs in Windows Search that can permit a hacker to remotely execute arbitrary code if a user either opens and saves a specially crafted saved-search file within Windows Explorer or clicks on a malicious search URL.
In addition to the critical bulletins, there are two others rated "important." The bulletins rated "important" plug security holes in SharePoint and Windows Media Center. The SharePoint bulletin fixes a privilege escalation issue. The Windows Media Center bulletin is focused on two vulnerabilities, the most serious of which can lead to remote code execution.