Tuesday, December 7, 2010

logging shell commands to syslog on secure systems

I had recently come across a blog post describing methods for capturing commands entered on the command line, and recording them to syslog.  Either by function() or by patching the actual shell itself.   I found this article because I was asked by my boss to find a way to add CLI logging to some hosts on our network, to support audits and accountability.

Some of the environments I work on are more secure than usual.  In a typical corporate environment, whether internet connected or not, there is generally no need or requirements to use system auditing to track all user actions.  Some government systems, whether classified or not, do require this, and some commercial systems in regulated industries, or who service government agencies, also require this level of auditing and accountability.  In some cases it can be a smart idea for non-regulated systemd.  For instance, if you're a managed services company that uses a team of operators to manage multiple customer environments, there may be some value to tracking user activity.

Most operating environments these days come with some sort of auditing facility, however I have found that these are usually fairly unintuitive, and most people that implement auditing do so by following a How-To, and then end up not actually having a SME on staff when things do go wrong.  Audit logs can also consume a lot of space, so lots of sysadmins just delete old audit logs in an effort to reclaim disk space.

One easy, and portable, way to quickly and intuitively audit user activity involves using patched shells to send all the commands run to syslog.  I should note that there are a few weaknesses in logging all commands to syslog, such as password exposure.  Some people do put passwords in the command line of such tools as ldapsearch, or mysql, or sqlplus.  Those passwords will then be recorded in plain-text in your system logs.

And there are always ways to work around being logged, like running a shell that doesn't log to syslog, which can be done as simply as by uploading your own, non-logging, shell and running it.

Aside from the weaknesses outlined above, though, in an environment where users are not malicious, and where team members can find themselves on any of a number of systems at any particular time, logging user can provide very valuable context in a familiar way.  And quickly, too.

Using syslogging shells is simply a tool like any other.  It doesn't replace real system auditing, but it definitely has it's place.

GNU Bash 4.1 has all the code to enable command logging, simply by editing the config-top.h file.
Just change:

/* Define if you want each line saved to the history list in bashhist.c:
   bash_add_history() to be sent to syslog(). */
/* #define SYSLOG_HISTORY */ 
#if defined (SYSLOG_HISTORY)
/* Define if you want each line saved to the history list in bashhist.c:
   bash_add_history() to be sent to syslog(). */
#if defined (SYSLOG_HISTORY)

And all commands in interactive shells are logged. (don't forget to add the other 9 official bash patches to get to code level 4.1.9)

One thing I did notice is that in Solaris, the PID was being logged with the log entry to syslog, however this was not the case in linux.  Rather the PID was being logged by the log entry %s itself.

if (strlen(line) < SYSLOG_MAXLEN)
 getpid(), current_user.uid, line);
Resulting in log entries like:
Dec  7 23:13:02 linux bash: HISTORY: PID=1752 UID=1001 ls
I don't really like that format, either. I'd rather see usernames and commands, and have the pid over on the left with the 'bash:'. This was a pretty simple change in code to:
  if (strlen(line) < SYSLOG_MAXLEN)
    syslog (SYSLOG_LEVEL, "[%s] %s", current_user.user_name, line);
This results in log entries that look like:
Dec  7 23:26:39 linux bash[1846]: [tkennedy] ls
To me, this is a much more readable log file. Perhaps that's because I'm used to the log format that the BOFH patched tcsh shell, which we also use, uses. Now bash and tcsh log in identical formats. Our users have been informed that bash and tcsh are acceptable for interactive shells on Linux, and there were no exceptions. On Solaris we encourage the use of bash or tcsh for interactive shells in the hopes that consistency lends itself to stability, although we use the RBAC aware pf- shells for role accounts like 'oracle' which encourage ksh.
Here's my patch to bashhist.c that logs entries the way I like them:

Friday, November 19, 2010

A generic perl script to scan a CIDR subnet for listeners on a specific port.

Ever had a customer ask you where *some process* was running on *some port* in their network? I have. And usually this involves an environment that doesn't have NMAP installed, or any other common port scanning tools. Fortunately these days, almost every *nix OS comes with Perl, even Solaris.

Since I work for a managed services company, and we manage a multitude of different environments, each with it's own set of restrictions and requirements, I try to write the most portable code that I can, so that it has the best chance of actually working in any given environment.

This script uses a couple of standard Perl modules that are included as part of the default installation, and don't require any CPAN-Fu, and it takes a couple of options, such as a switch for verbosity, and IP address, with or wirhout a CIDR mask, and a TCP port. The CIDR mask defaults to /32, and the port defaults to 22. Here's an example of the output.

tcsh-[101]$ ./scan-port.pl 80
Request to scan on Port 80 (http)
Scanning 4 IP Addresses:
--------------------------------------------------------------------------------    : rats.entic.net                   : listening on 80 (http)    : corn.entic.net                   : listening on 80 (http)    : ice.hostsonfire.co.uk            : listening on 80 (http)    : jeep.sugarat.net                 : listening on 80 (http)
Found 4 hosts listenening on port 80.

And here's the script itself.
#!/usr/bin/env perl
# scan_port.pl (c) tkennedy - 2011 November 19 Version 1.1
# Description: Allows scanning a IP Subnet for TCP listeners on designated port.
# Syntax: $0 [-v] IPADDRESS/CIDR-NETMASK [Port]
# Purpose:
# This script provides a means of scanning a subnet for TCP listeners, using 
# only commonly available Perl functions.  This should make the script portable
# to any system with Perl installed.  The script can be passed 3 arguments. 2 of
# the arguments are optional, and include a '-v', which increases the verbosity
# of script output, and 'P', which is a TCP port presented as an integer between
# 1 - 65535.  If a port is not supplied on the command line, the script assumes
# a default of 22, which is the common port for Secure Shell traffic (ssh). The
# mandatory argument is an IP Address, either with, or without, a CIDR netmask.
# If a CIDR netmask is not supplied on the command line, then we assume you only
# intend to scan a single IP (ie, a /32).
# History:
# 20101123 1.1 tkennedy - removed Switch module for Sol8/Perl5.003 compatibility
# 20101119 1.0 tkennedy - initial revision
# The modules we're using are standard perl modules, so this script should 
# work on any operating system with Perl installed.
use strict;
use IO::Socket;

my ($ip,$cidr,$port,$target);
my $VERBOSE = 0;

# We need a regex to match IP addresses.  This is only used to validate
# the command-line options to verify that one option is an IP.
my $ipr = qr/^((?:(?:2(?:5[0-5]|[0-4][0-9])\.)|(?:1[0-9][0-9]\.)|(?:(?:[1-9][0-9]?|[0-9])\.)){3}(?:(?:2(?:5[0-5]|[0-4][0-9]))|(?:1[0-9][0-9])|(?:[1-9][0-9]?|[0-9])).*$)/x;

# I wanted to keep things as free-form as possible, and so opted to just 
# parse the command line to extract our options.  This also gives us some
# leeway to ignore bad options.
# In our parser, we will match a '-h' for help info, a '-v' to extend 
# our output a bit, including printing lines for hosts that are scanned
# but not listening.  We'll also match a single number, which we'll 
# interpret as a TCP port number, and lastly, we'll match an IP address
# or CIDR-masked sub-net.
foreach my $arg (@ARGV) {
 for ($arg) {
  if ( $arg eq '-h' )  { &usage; }
  elsif ( $arg eq '-v' )  { $VERBOSE = 1; }
  elsif ( $arg =~ m/^\d+$/ )  { $port  = $arg; }
  elsif ( $arg =~ m/$ipr/ )  { $target = $arg; } 

# if the user forgot to put in a target subnet, goto usage();
&usage("Error: no target supplied!") if ("$target" == "");

# Here we'll set the default port to "22", which is SSH, and then we'll
# check to see if a port was submitted on the command line.  If it was,
# we'll override the default with the user submitted value.  We'll do 
# the same for CIDR mask, assuming that if a mask was not passed in, then
# the user wants a single host scanned and use /32 as the default.
($ip,$cidr) = split( /\//, $target);
$cidr  = ( $cidr ? $cidr : "32" );
$port  = ( $port ? $port : "22" );

# die if we get an invalid CIDR mask!
&usage("Error: Invalid CIDR mask [$cidr]") if ( $cidr > 32 );

# Get the TCP Service name for our port...
my $svcname = getservbyport($port,"tcp");

# Convert the CIDR mask into a hex netmask, and calculate the number
# of addresses in the supplied target.
# my $mask = 0xffffffff >> $cidr;  # this fails on sol8/perl-5.003
my $size = 1 << ( 32 - $cidr );
my $mask = $size - 1;

# script body below here.

print "Request to scan ${ip}/${cidr} on Port $port ($svcname)","\n";
print "Scanning $size IP Addresses:","\n";

# calculate the lowest IP in the range, by AND-ing the supplied IP 
# address and the netmask, and convert to dotted quad notation.
my $lowest      = unpack('N', pack('C4', split '\.', $ip)) & ~$mask;
my $count = 0;
my $scanned = 0;

# based on the $lowest IP in the subnet, let's enumerate all of the
# IP addresses in the supplied $target subnet.
my @ips  = map {$lowest++} 0 .. $mask;

# a simple loop to scan each of the ips we mapped.
foreach my $addr(@ips) {

print "Found $count hosts listenening on port $port.","\n";

# only subroutines are below here.

sub scan_ip {
 # from the foreach loop above, we've passed in our address.
 # this address is an integer, so we'll need to convert it to
 # a dotted-quad format IP address. then try hostname lookup,
 # and then try opening a socket.
 my $addr = shift;
 my $ipaddr = join( '.', unpack( "C4", pack( "N", $addr ) ) );

 my $hostname = gethostbyaddr(inet_aton("$ipaddr"), AF_INET);
 chomp $hostname;

 if ("$hostname" eq "") {
  $hostname = ( $VERBOSE ? "NXDOMAIN" : " " );

 my $sock = IO::Socket::INET->new(
  PeerAddr => "$ipaddr",
  PeerPort => "$port",
  Timeout => "1",
  Proto => "tcp",
  ) or nosocket("$ipaddr","$hostname") && next;

 if($scanned < 1) { &hr(); }
 my $txt = "listening on $port ($svcname)";
 printf('%-15s : %-32s : %-15s', $ipaddr, $hostname, "$txt\n") if($sock);

 close($sock) if($sock);

sub nosocket { 
 # we reach this sub on unsuccessful socket attempts.
 if($scanned < 1) { &hr(); }
 my $ipaddr = shift;
 my $hostname = shift;

 if($VERBOSE > 0) {
  my $txt = "closed on $port ($svcname)";
  printf('%-15s : %-32s : %-15s', $ipaddr, $hostname, "$txt\n");


sub usage { 
 if (@_) {
  print "\n@_\n";
 # this sub() just prints the standard usage information.
 print < [port]
 -h  this message
 -v  verbose output
  format IP/CIDR:, /32 is default CIDR mask
 [port]  a tcp port between 1 and 65535, 22 is default 

Example: $0 -v 80
 will scan the 255 addresses in the subnet on port 80


sub hr { 
 # print a row of ---s
 print "-" x 80, "\n";

sub hr2 { 
 # print a row of ===s
 print "=" x 80, "\n";

So far this has worked successfully on Solaris 10 Sparc & x64, CentOS 5.5 x64, Solaris 8 Sparc, and Solaris 9 Sparc, and Mac OS X 10.6.