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MS confronts another IIS system-level hole

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Microsoft IIS is open to total exploitation by an attacker who can establish a Web session and execute a buffer overrun against an ISAPI (Internet Server Application Programming Interface) extension which contains an unbounded buffer. The result would be system-level access, enabling an attacker to run arbitrary code against the machine, or make file and setup modifications of his or her choice.

All IIS implementations running on default installations of Win-NT 4.0, Win-2K, or Win-XP are affected.

The culprit here is idq.dll, a component of Index Server (or 'Indexing Service' in Win-2K) which supports administrative scripts (.ida files) and Internet data queries (.idq files).

According to the relevant MS security bulletin, idq.dll contains an unchecked buffer in a section of code which handles input URLs. Idq.dll runs in the System context, so an attacker would be able to gain complete control of the server.

Furthermore, the indexing service would not have to be running in order to exploit the machine. So long as the script mapping for .idq or .ida files is present, the vulnerability can be exploited, Microsoft warns.

The vulnerability was discovered by eEye Security, and is one of the most damaging holes in IIS yet reported -- on a par with the unchecked buffer in the IIS .printer ISAPI filter, which eEye also discovered back in April.

Redmond is not mincing words with this one. "This is a serious vulnerability, and Microsoft urges all customers to take action immediately," the company says.

It should be enough to remove the script mappings where one can be confident that no further modifications will be made to the system; but if a system is open to tinkering by many hands, this is definitely not a safe way to go.

"It is possible for [script mappings] to be automatically reinstated if additional system components [like service packs and hotfixes] are added or removed. Microsoft recommends that all customers using IIS install the patch, even if the script mappings have been removed," the security bulletin says.

There are patches now for NT 4.0 and most flavors of 2K; and the hole will be fixed in the consumer release of XP. Unfortunately, XP beta users are totally out of luck, and 2K Datacenter Server customers need to get their patches from the OEM.

Otherwise, everything is under control. ®

Related Links

Win-NT 4.0 patch
Win-2K patch

SANS - Survey on application security programs

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