proc_net_parser for /proc/net/tcp [udp]

Transform /proc/net/tcp [udp] to human readable format in .csv file

Based on the script Ruan Tannhäuser here

Some changes script of Ruan Tannhäuser

• Display of errors is hidden for those versions of awk where there is no parameter --version
• Added display of UID value
• Added the ability to specify an arbitrary .txt file in the /proc/net/tcp [udp] format
• Other minor changes

Why is it needed

Immediately I can name at least two purposes of use this Bash-script:

• Using a script in docker containers where there are no commands like:
  • netstat
  • ss
• Using a script for LFI (Local File Inclusion) vulnerability purposes. When we have the ability to read files on the host, we can try to read the /proc/net/tcp [udp] file, save it to a separate file and pass it to the input of the script in order to see open ports with the UID of the users under which the processes are running. Useful for pentesting, CTF, etc.

Install and run

There are two possibilities to install the script:

1. Standardly use like any other Bash-script
2. Add the proc_net_parser() function to your .bashrc file

Let's take a look at each installation and use method in turn.

Run the proc_net_parser.sh as like a regular Bash-script:

$ ./proc_net_parser.sh /proc/net/tcp
ID,Source,Destination,Status,UID
0,127.0.0.1:7337,0.0.0.0:0,TCP_LISTEN,1001
1,127.0.0.1:50505,0.0.0.0:0,TCP_LISTEN,0
2,127.0.0.1:34391,0.0.0.0:0,TCP_LISTEN,1000
3,127.0.0.1:33060,0.0.0.0:0,TCP_LISTEN,130
4,127.0.0.1:631,0.0.0.0:0,TCP_LISTEN,0
5,127.0.0.1:3306,0.0.0.0:0,TCP_LISTEN,130

You can also save the output to a .csv file:

$ ./net_parser.sh /proc/net/tcp > out.csv
$ head out.csv 
ID,Source,Destination,Status,UID
0,127.0.0.1:7337,0.0.0.0:0,TCP_LISTEN,1001
1,127.0.0.1:50505,0.0.0.0:0,TCP_LISTEN,0
2,127.0.0.1:34391,0.0.0.0:0,TCP_LISTEN,1000
3,127.0.0.1:33060,0.0.0.0:0,TCP_LISTEN,130
4,127.0.0.1:631,0.0.0.0:0,TCP_LISTEN,0
5,127.0.0.1:3306,0.0.0.0:0,TCP_LISTEN,130
6,127.0.0.1:3001,0.0.0.0:0,TCP_LISTEN,1
7,0.0.0.0:8000,0.0.0.0:0,TCP_LISTEN,1000
8,0.0.0.0:3790,0.0.0.0:0,TCP_LISTEN,0

Suppose we have a .txt file which contains data in /proc/net/tcp format:

$ head proc_net_tcp.txt
sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode                                                     
   0: 0100007F:8124 00000000:0000 0A 00000000:00000000 00:00000000 00000000   109        0 32352 1 0000000000000000 100 0 0 10 0                     
   1: 0100007F:9997 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1001        0 2038837 1 0000000000000000 100 0 0 10 0                   
   2: 0100007F:A365 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1001        0 2039636 1 0000000000000000 100 0 0 10 0                   
   3: 0100007F:1388 00000000:0000 0A 00000000:00000002 00:00000000 00000000    33        0 32941 3 0000000000000000 100 0 0 10 0                     
   4: 3500007F:0035 00000000:0000 0A 00000000:00000000 00:00000000 00000000   102        0 29909 1 0000000000000000 100 0 0 10 5                     
   5: 0100007F:15B3 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1001        0 32408 1 0000000000000000 100 0 0 10 0                     
   6: 0100007F:0CEA 00000000:0000 0A 00000000:00000000 00:00000000 00000000   109        0 32362 1 0000000000000000 100 0 0 10 0                     
   7: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 32834 2 0000000000000000 100 0 0 10 0                     
   8: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 32822 1 0000000000000000 100 0 0 10 0 

In this case, we can also pass it to the script:

$ ./net_parser.sh /home/nikn0laty/proc_net_tcp.txt | head
ID,Source,Destination,Status,UID
0,127.0.0.1:33060,0.0.0.0:0,TCP_LISTEN,109
1,127.0.0.1:39319,0.0.0.0:0,TCP_LISTEN,1001
2,127.0.0.1:41829,0.0.0.0:0,TCP_LISTEN,1001
3,127.0.0.1:5000,0.0.0.0:0,TCP_LISTEN,33
4,127.0.0.53:53,0.0.0.0:0,TCP_LISTEN,102
5,127.0.0.1:5555,0.0.0.0:0,TCP_LISTEN,1001
6,127.0.0.1:3306,0.0.0.0:0,TCP_LISTEN,109
7,0.0.0.0:80,0.0.0.0:0,TCP_LISTEN,0
8,0.0.0.0:22,0.0.0.0:0,TCP_LISTEN,0

Consider an alternative installation option via the .bashrc file:

1. In your .bashrc file, you need to add the function proc_net_parser() itself to the end, like this:

proc_net_parser() {
    if [ $# -ne 0 ]
    then
        awk $([[ $(awk --version 2> /dev/null) = GNU* ]] && echo --non-decimal-data) '
            function hex2addr(hex) {
                split(hex, data, ":");
                l = length(data[1]);
                dec_ip = sprintf("%d", "0x" substr(data[1], l - 1, 2));
                for(i = 1; i < 4; i++){
                    dec_ip = sprintf("%s.%d", dec_ip, "0x" substr(data[1], l - (i * 2 + 1), 2))
                };
                return sprintf("%s:%d", dec_ip, "0x" data[2]);
            }
            {
                if ($1 == "sl") {
                    printf "ID,Source,Destination,Status,UID\n";
            } else {
                split($1, conn, ":");
                src = hex2addr($2);
                dst = hex2addr($3);
                status_str = "TCP_ESTABLISHED,TCP_SYN_SENT,TCP_SYN_RECV,TCP_FIN_WAIT1,TCP_FIN_WAIT2,TCP_TIME_WAIT,TCP_CLOSE,TCP_CLOSE_WAIT,TCP_LAST_ACK,TCP_LISTEN,TCP_CLOSING,TCP_NEW_SYN_RECV,TCP_MAX_STATES";
                split(status_str, status, ",");
                status_index = sprintf("%d", "0x" $4)
                uid = $8
                printf("%d,%s,%s,%s,%s\n", conn[1], src, dst, status[status_index], uid);
            }
        }' $1
    else
        echo "--[proc_net_parser for /proc/net/tcp]--"
        echo "Please specify a file, for example: ./proc_net_parser.sh /proc/net/tcp";
  fi
}

2. Restart your terminal
3. Use the function like this (in fact, everything is the same, just do not specify the name of the script file):

$ proc_net_parser /proc/net/tcp | head 
ID,Source,Destination,Status,UID
0,127.0.0.1:7337,0.0.0.0:0,TCP_LISTEN,1001
1,127.0.0.1:50505,0.0.0.0:0,TCP_LISTEN,0
2,127.0.0.1:34391,0.0.0.0:0,TCP_LISTEN,1000
3,127.0.0.1:33060,0.0.0.0:0,TCP_LISTEN,130
4,127.0.0.1:631,0.0.0.0:0,TCP_LISTEN,0
5,127.0.0.1:3306,0.0.0.0:0,TCP_LISTEN,130
6,127.0.0.1:3001,0.0.0.0:0,TCP_LISTEN,1
7,0.0.0.0:8000,0.0.0.0:0,TCP_LISTEN,1000
8,0.0.0.0:3790,0.0.0.0:0,TCP_LISTEN,0