Microsoft has issued six security advisories for nine vulnerabilities, including a server-side remote procedure call vulnerability that needs no user interaction to trip a denial of service.
Other patches fix a trio of Internet Explorer zero-day flaws that could lead to system hijacking and a Word flaw thats being actively exploited even though theres been no public discussion of it.
But some security experts are tagging another critical vulnerability—in Outlook Express and Windows Mail—as potentially the worst of the bunch, given that these applications are installed on nearly every Windows release.
The critical security update, detailed in Microsofts MS07-056 security bulletin, addresses a bug in how Outlook Express handles news files.
The flaw involves viewing news from Web sites via a protocol called NNTP (Network News Transfer Protocol). A remote attacker could rig a site that could claim to post news using the NNTP protocol but in reality would be slipping malware onto the targeted system. If a victim used Outlook Express to view the purported news items, the vulnerability would be exploited and could allow remote code execution due to the way Outlook Express handles a malformed NNTP response.
Another critical flaw exists in Kodak Image Viewer, a preinstalled program, which could lead to system takeover on Windows 2000. It could also affect Windows XP or Windows Server 2003 systems that were upgraded from Windows 2000. The vulnerability, covered in Microsofts MS07-055 security bulletin, can lead to remote code execution if the user of a vulnerable system is tricked into viewing a rigged image.
Another critical advisory is MS07-57, which addresses three zero-day vulnerabilities in Internet Explorer. The most serious vulnerability of the trio, a URI-handing flaw, could allow remote code execution if a user gets tricked into viewing a malicious Web page with IE.
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Microsofts update addresses three of the IE vulnerabilities by not allowing the browser window content to persist after navigation. The update addresses a fourth vulnerability by modifying script error exception handling so that no attempt is made to access the freed memory.
Microsoft is also addressing a denial-of-service vulnerability in RPC (remote procedure call) in its MS07-058 security bulletin. The DOS flaw is due to a failure to communicate with the NTLM (NT LAN Manager), a Microsoft authentication protocol used with the SMB protocol when authenticating RPC requests.
Microsoft may have rated the RPC DOS as an important update, but some security experts say theyre telling corporate clients to push it to the top of the priority list of fixes, given that exploitation doesnt require users to lift a finger.
"Id flag this as one of most important," said Eric Schultze, chief security architect at Shavlik Technologies, based in Rosedale, Minn. "Simply by having your machine on the network, an evil attacker can send packets that cause it to fall the off network and sometimes to reboot."
The vulnerability—for which Schulze said he expects to see an exploit soon—affects Windows 2000, Windows XP, Windows Server 2003 and Windows Vista.
Another critical flaw is in Word, addressed in Microsofts MS07-060 bulletin. The Word vulnerability could lead to a targeted system being hijacked by a remote attacker if a victim is successfully tricked into opening a rigged Word file sent in e-mail or posted on a site.
The Word bug was privately reported to Microsoft and hasnt been publicly discussed. Still, the exploit is being actively exploited on the Internet.
Finally, Microsoft is fixing a problem that could result in escalation of privilege in Windows SharePoint Services 3.0 and Office SharePoint Server 2007 within the SharePoint site. The vulnerability, addressed in bulletin MS07-059, could also allow an attacker to run arbitrary script to modify a users cache, resulting in information disclosure at the workstation.
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