source: http://www.securityfocus.com/bid/5547/info

A directory traversal vulnerability has been reported for Abyss Web Server. The issue is related to the failure to properly process the backslash '\', encoded as '%5c', character, which may be used as a directory delimiter under these platforms. By using the URL encoded sequence '%2e%2e%5c', the web root may be escaped.

Exploitation can result in arbitrary system files being sent to a remote attacker. This information may be of value in attempting further attacks against the vulnerable system.

This issue is reported to have different effects in a different environments.

http://host/%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cwinnt%5cwin.ini
"GET /\..\..\..\..\..\winnt\win.ini HTTP/1.0" (using a Telnet client)
http://host/%5c%2e%2e%5c%2e%2e%5c%2e%2e%5c%2e%2e%5cwinnt/
http://host/%2f%2e%2e%2f
http://host/%2f%2e%2e%2fcgi-bin/