debian-security  

Funny story about mysteriously open port 21

Sir Conquer
Tue, 09 Mar 2010 00:21:56 -0800

As I was testing new iptables rules on my remote Lenny server, port 21 kept 
coming up as open, yet nothing was listening on it (according to netstat and 
lsof). At which point I'm panicking and wondering whether I've been owned! The 
panic had productive side-effects, as I discovered several misconfigurations in 
Bind. Still, no matter where I poked - I could not figure out what the hell is 
opening the damn ftp port... After making sure that I'm thoroughly dropping all 
traffic from APNIC subnets, and as I was getting ready to post a question about 
my dilemma here - I had a eureka moment - I'M RUNNING FTP PROXY on my LAN 
gateway! LOL :-) I laughed so hard that I woke-up (and pissed-off) my wife!

Just thought I'd share this with you guys, so that next time someone in the 
same shoes googles "mysteriously open port 21", as I did, they'll get this 
reminder to check their gateway and/or proxy settings. :-)

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