After additional analysis of the Microsoft Print Spooler Service vulnerability, which Microsoft first described August 9 in a bulletin released that day, Symantec alerted customers of its DeepSight Threat Management System to patch the flaw immediately or risk attack.
"We always take the conservative viewpoint in our alerts," said Alfred Huger, the senior director of engineering for Symantec's security response team. "But when we release an alert, we're urging people to patch as soon as possible."
In fact, said Huger, although an exploit has not been seen in the wild, one will. "There's always someone who's smart enough to figure things out, and the law of averages say that an exploit will appear."
In fact, exploits have already been published privately among hacker groups, and are in the hands of customers of vulnerability tools like Immunity's Canvas. Symantec said it wasn't sure whether Immunity's exploit was only proof-of-concept code or what it called a "robust exploit" that could actually attack systems remotely.
Microsoft's original bulletin, marked as MS05-043, rated the bug as "critical," the Redmond, Wash.-based developer's highest alert warning for vulnerabilities. On Windows 2000 PCs, as well as Windows XP and Windows XP SP1, the win32.spl.dll can be exploited remotely via the RPC interface -- the same service used by the dangerous and damaging MSBlast two years ago this month -- and attacked anonymously, in other words, by anyone, even those without a legitimate log-in account.
Windows XP SP2 and Windows Server 2003 are not anonymously exploitable, both Microsoft and Symantec agreed, because of that version's more stringent checks in the RPC interface.
Symantec uncovered other new information lacking in Microsoft's original bulletin, specifically that Windows XP and XP SP1 are vulnerable through the guest account that is enabled by default in some configurations. (A week ago, Symantec discovered the possible exploit of Windows XP and XP SP1 by Zotob-like bots, and Microsoft responded with a new security advisory offering recommendations on how to stymie such attacks.)
If all this sounds familiar, it should. The most vulnerable systems, Windows 2000, and the guest account vulnerabilities of Windows XP and XP SP1 are characteristics shared with the Plug and Play vulnerability that resulted in the widespread Zotob bot worm attacks earlier in August.
"There are things in common between the two," said Huger, "although the way to get at [the vulnerabilities] is different."
"After analyzing the vulnerability in detail it is believed that this vulnerability could also become an attack vector used by a worm against the Windows 2000 and Windows XP SP1 and below systems," Symantec's alert read in part.
Huger confirmed the seriousness of the threat. "This could be dropped into bots, just like Zotob," he said. "Or placed in Metasploit, which is the de facto break-in tool from Unix platforms."
"Absolutely, users should patch this vulnerability immediately," Huger warned, because once a working exploit is available, bot worms in the Zotob style are inevitable.