Zero-Day SQL Server Flaw Could Allow Remote Code Execution

Microsoft is warning users of a zero-day vulnerability discovered in SQL Server, and that exploits of the flaw have already been published.

The software giant yesterday issued a security advisory outlining a flaw that could allow remote code execution on many versions of SQL Server. The company has not had time to develop a patch, but it is offering some "workarounds" that it says will alleviate the problem.

Although exploits are out on the Internet, "Currently, Microsoft is not aware of active attacks that use this exploit code or of customer impact at this time," the advisory states.

According to one source, the initial exploit was published by the same "researcher" who discovered the flaw. "This is an example of irresponsible disclosure," says Eric Schultze, CTO at Shavlik Technologies. "The person that found that issue took the proper steps to report it to Microsoft. However, they grew impatient with Microsoft and decided to release exploit code before Microsoft announced a patch.

"This so-called security researcher has therefore placed thousands of servers and potentially untold number of persons' personally identifiable information at risk for purposes of their own popularity," Schultze continues.

Schultze suggests that the recent discovery of zero-day bugs in Microsoft's Internet Explorer 7 has proved that Websites are susceptible to SQL injection attacks, "which are now vulnerable to more serious attacks using this zero-day SQL flaw. In other words, what was bad has now become worse." NSS Labs late last week published a study that shows most popular endpoint security software packages can do little to stop attacks that exploit the IE 7 bug.

The new SQL Server bug is an authenticated remote code execution vulnerability that exists in the MSSQL extended stored procedure, "sp_replwritetovarbin," due to an invalid parameter check, Microsoft says. "All systems running one of the affected Microsoft SQL Server software where a malicious user is allowed to log on are at risk of exploitation of this vulnerability." Microsoft says. "In addition, Web applications with a SQL Server back-end database are at risk if a SQL Injection vulnerability exists."

Microsoft says the new SQL Server zero-day may not be as easy to exploit as the IE7 glitch. "This vulnerability is not exposed anonymously," the advisory states. "An attacker would need to either authenticate to exploit the vulnerability or take advantage of a SQL injection vulnerability in a Web application that is able to authenticate." MSDE 2000 and SQL Server 2005 Express do not allow remote connections, so an authenticated attacker would need to initiate the attack locally to exploit the vulnerability, the company says. Until a patch can be issued, Microsoft is recommending a workaround that requires users to disable the "sp_replwritetovarbin" extended stored procedure. This workaround only affects customers who use transactional replication with updatable subscriptions in SQL, which is only a fraction of those who use SQL Server, the company says.

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