First, the good news - it's not a flaw in the operation of Windows Firewall on Windows Vista. It's a design feature, it makes sense, and it fits in with the principle that the firewall should keep out unsolicited traffic. It's not really a hole, but I thought I'd grab your attention.

The symptom first came up in a Usenet posting (thanks, Jesper, for bringing me in) about Vista and a third-party FTP client:

When I do a directory listing, and a PORT command is issued, and the
server attempts to connect, it works, but at the same time a dialogue
appears telling me it's blocked, and I can keep blocking or unblock.
I choose keep blocking but it doesn't actually block it once.

Here's how it looks.

First, if you haven't got a third-party FTP client let's fake it, by copying Microsoft's command-line FTP client from the Windows System32 directory to another directory:

C:\users\MyMe> copy %windir%\system32\ftp.exe
1 file(s) copied.

The FTP client will not display prompts to you, but that's a minor issue - if it upsets you, try downloading a third-party client and trying it.

Anyway, here we go - let's try the issue in question:

• Type ftp ftp.microsoft.com
• After you see the "200" greeting message, enter ftp as the user - press enter.
• Now you're prompted for a password - enter anything and press enter.
• Once you're logged on, enter dir - again, press enter.
• You'll see the directory listing succeed, but you'll also see a warning that a connection is being blocked:

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Microsoft, Windows Vista, Security, Firewall, Vulnerability, Knowledgebase, FTP, TCP/IP