Another major security hole has been found in Internet Explorer which makes system access possible across all Windows plaforms through a boundary error when connecting to a file server. Windows Explorer is also affected.

Microsoft has issued an advisory in which it claims the problem was corrected in XP service pack 1 and service pack 4 for Windows 2000. However, security company Secunia claimed that the vulnerability still existed in fully-patched systems.

Microsoft has also only listed Windows XP and 2000 as vulnerable but Secunia says that it also affects 95, 98 and Me. It is still investigating NT4 and 2003. A note in the Secunia advisory also explains why it has given the problem a "highly critical" status: "Secunia would normally rate this kind of vulnerability as 'moderately critical', since this kind of traffic should be restricted to a LAN via border routers and firewalls. However, this is not the case on many networks, which leads to the higher rating."

The actual hole is caused by setting up a malicious file server with a hugely long name (300 bytes). It can be used to cause a buffer overflow and then to run code on the host machine. In practical terms, we're looking at system access if someone can be conned to click on a particular link.

Microsoft, at least according to Secunia, doesn't have a patch so the only solution is to watch firewalls and routers to check on the traffic. That and disable "client for Microsoft Networks" for network cards.

The hole was discovered by Rodrigo Gutierrez.