Core Security Technologies discovered thatcould be exploited using the to spread across the Internet in just minutes.
Researchers determined that an attacker could use a recently patched Microsoft flaw to create a fast-moving worm.
An attacker doesn't have to individually address computers on the network, but can broadcast an attack. Such a tactic could actually create a worm that spreads faster than the disruptive SQL Slammer worm did last year.
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"We believe these new attack vectors make the vulnerability even more dangerous and critical as the proposed workarounds are not sufficient to close them and particularly because they outline a very plausible scenario for a highly efficient worm," Ivan Arce, chief technology officer for security software maker Core Security Technologies, wrote in an e-mail to CNET News.com.
The company's report also found that flaws in the Windows Messenger service, which allowed, could be exploited using the same "fire-and-forget" user datagram protocol (UDP) packets. The packets don't require two computers to establish a connection, which takes time. Instead, the source computer can quickly send out the packets and not worry about whether they reach their destination.
The research determined that an attacker doesn't have to individually address computers on the network, but can broadcast an attack. Such a tactic could actually create a worm that spreads faster than the SQL Slammer worm did last year.
Core ST notified Microsoft of the increased seriousness of the vulnerability on Tuesday, but hadn't heard back from the company by late in the day, Arce said. Because a patch had already been released for the vulnerability, Core ST didn't feel obligated to wait for a Microsoft reply before publicly disclosing the vulnerability, he said.
When contacted by CNET News.com, Microsoft urged customers to apply the patch and stressed that new ways of exploiting flaws are constantly emerging.
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"There is no caveat that there will never be another attack vector," said Iain Mulholland, a security program manager for Microsoft. "It is rated as critical because we believe it is critical. Applying the patch does correct the problem."
Core ST acknowledged that the patches will prevent the attacks and also urged people to apply the fixes. However, the company warned that the workarounds that Microsoft had previously specified in its bulletins will not protect against an attack via UDP packets. Such data also can be configured in such a way to bypass most firewalls.
Microsoft's security site contains more information on the flaws and fixes.