+------------------------------------------------------------------+ | Linux Security: Tips, Tricks, and Hackery | | Published by Onsight, Inc. | | | | 15-May-2003 | | http://www.hackinglinuxexposed.com/articles/20030515.html | +------------------------------------------------------------------+ This issue sponsored by Nmap - The ultimate network port mapping tool. Nmap was featured in a cracking session by Trinity in the new Matrix: Reloaded movie. In recognition to Fyodor's contribution to the real and virtual world, I think we should all lobby for Fyodor to get the recognition he deserves: a photo of him with Carrie-Anne Moss. http://www.insecure.org/nmap/ -------------------------------------------------------------------- Who's listening on that port? By Brian Hatch Summary: Tracking down your network daemons is extremely easy if you use the right tools. Last week a reader asked the following question: "I'm having trouble tracking down a process that's running on my machine. When I run netstat -a, I see lots of things that should be there, but also the following: $ netstat -a Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:imaps *:* LISTEN tcp 0 0 *:smtp *:* LISTEN ... tcp 0 0 *:8577 *:* LISTEN ... I can't figure out what that is on port 8577. Any ideas?" My first reaction is almost universally to connect and see if it says anything useful. So I had him pull out netcat[1] to check the header: $ nc localhost 8577 RFB 003.003 The server process responded with the RFB line. That's what you get when you connect to a VNC server, just like you'd expect "SSH-1.99-OpenSSH...." for an SSH server that supports v1 and v2. Most network daemons will say something when you connect. You can usually match the output (aka the banner) to a protocol or process. However there are two other ways that are even more direct, that can tie the network port to the actual process that is listening. For example on the machine running the VNC server on port 8577, there was no process called "vncserver" running on the machine. So, we turn to two tools: netstat, and our old friend lsof. Netstat has a '-p' option that will show you the name and pid (process id) of the local process that is associated with a connection. If you're running as root, you can see the processes for all users. If you're a normal user, you can only see the processes that are running as you. So, re-running the netstat above with '-p' would have yielded # netstat -ap Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:imaps *:* LISTEN 277/stunnel tcp 0 0 *:smtp *:* LISTEN 394/master ... tcp 0 0 *:8577 *:* LISTEN 57283/bash ... # ps -fc 57283 UID PID PPID CLS PRI STIME TTY STAT TIME CMD doug 57283 1 - 29 10:30 ? S 0:00 /home/doug/bin/bash So here we can see that /home/doug/bin/bash (a copy of vncserver under a different name to avoid detection) is the process listening on port 8577, and it can be killed and doug scolded as appropriate. Alternatively, you can use lsof to do the same thing # lsof -i tcp:8577 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME ssh 57283 doug 3u IPv4 31740 TCP *8577 (LISTEN) If you're interested in what the process is doing, you can use 'lsof -p' to see it's open files, 'strace -p' to watch it's system calls, or 'ltrace -p' to watch library calls. If you're comfortable with full blown debugging, gdb can attach to it and give you all the control you could want.[2] NOTES: [1] You could use telnet too, but why? [2] All of these actions require that you're root unless you own the process. ------------- Brian Hatch is Chief Hacker at Onsight, Inc and author of Hacking Linux Exposed and Building Linux VPNs. He likes to keep the number of open ports on his machines to a minimum. All his machines really need is XOR-Telnet for ultimate session security. Brian can be reached at brianat_private -------------------------------------------------------------------- This newsletter is distributed by Onsight, Inc. The list is managed with MailMan (http://www.list.org). You can subscribe, unsubscribe, or change your password by visiting http://lists.onsight.com/ or by sending email to linux_security-requestat_private Archives of this and previous newsletters are available at http://www.hackinglinuxexposed.com/articles/ -------------------------------------------------------------------- Copyright 2003, Brian Hatch. - ISN is currently hosted by Attrition.org To unsubscribe email majordomoat_private with 'unsubscribe isn' in the BODY of the mail.
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