Microsoft to Make MSN Messenger Fixes Mandatory

Microsoft flips the switch on mandatory upgrades for MSN Messenger users after a high-risk exploit code is posted on the Internet.

Microsoft Corp. on Friday lashed out at two security research firms for publishing proof-of-concept exploit code for MSN Messenger hours after Microsoft released security patches for the product.

In one instance, the software giant said malicious hackers have modified the proof-of-concept code into an exploit that puts millions of users at risk of code execution attacks that require no user interaction.

Moving swiftly to blunt an attack, Microsoft has decided to push out patched versions of MSN Messenger as a mandatory update. As of Thursday evening, users of the popular instant messaging client must update to MSN Messenger version 6.2.0205 or the MSN Messenger 7.0 beta before they are allowed to log on.

"When the vulnerability was announced this week we initially introduced an optional upgrade and had plans to make the upgrade mandatory," a Microsoft spokesperson said. "But when we learned that detailed exploit code had been published on the Internet we felt the need to take decisive action."

According to the exploit code seen by, an attacker need only load a malicious PNG (Portable Network Graphics) file as a buddy icon to launch an attack against every MSN Messenger user on a buddy list.

Core Security Technologies, the research company that found and reported the flaw, confirmed that the published exploit code could be used to launch blind attacks.

"The target doesnt even have to communicate with the attacker. Once the attacker has the targets MSN Messenger contact on his contact list, he can launch an attack without the target even knowing," said Max Caceres, director of product management at Core Security.

Even worse, Caceres told that the attacker could take control of the infected machine and change the targets display to replicate the attack against everyone on that buddy list.

"This could lead to a massive, widespread attack unless all MSN Messenger users apply the upgrades," he said.

Microsoft late Thursday released a security advisory to warn customers of the risk. The company also provided step-by-step instructions in a separate notice for both consumer and enterprise MSN Messenger users.

/zimages/6/28571.gifClick here to read about an MSN Messenger worm that can be used to hijack system information.

Microsoft pinned the blame for the exploit code squarely on the shoulders of Core Security, alleging that the public exploit is based on proof-of-concept code released by the Mass.-based information security firm.

[Core Security] published proof-of-concept code on the Internet the same day Microsoft issued Security Bulletin MS05-009 to resolve the issue. Since then, a separate individual has modified the posted code into exploit code," Microsoft said in a strongly worded statement.

"[T]he publishing of proof-of-concept code within hours of the security updates being made available has put customers at increased risk."

Caceres dismissed the Microsoft accusation and pointed out that engineers at Core Security worked closely with Microsoft since reporting the vulnerability in August 2003.

"We worked with Microsoft for six months to develop this patch. We waited until they released the fix before we published our advisory," Caceres said, arguing that it is common procedure to provide proof-of-concept code to let businesses determine whether their systems are secure.

Next page: How to protect against an exploit.