Building a Secure Environment for Free

Freeware Security Tools You Need

Randy Marchany

VA Tech Computing Center

Blacksburg, VA 24060

[email protected]

540-231-9523

Suggested Strategy

Use freeware tools to gain experience with your system/network environment.

Gain experience with the features provided by these tools in order to better analyze a vendor tool.

Freeware tools provide a good short-term solution.

Vendor tools may provide better long-term solution.

The Tools

Audit/Port Scanning Tools– Nessus– Saint– Sara– Nmap, strobe– Tripwire, AIDE

“Personal” Firewall– TCP Wrappers– Portsentry,ipfilters– ZoneAlarm, BlackIce, NeoWorks

The Tools

Syslog Scanners– Logcheck

Sniffers– Snoop, iptrace, tcpdump– Netwatch (NT)– Snort

The Tools

Sysadmin Tools– Big Brother– Password Checkers

• Crack, nt-crack, l0phtcrack,npasswd, passwd+

– Lsof, inzider (NT)– Sudo (unix)

Remote Control Tools– VNCviewer

Homegrown Tools– Network Mgt Tools that can be used for Incident Response

Audit/Port Scan Tools

These tools can be used to scan your systems and network for vulnerabilities.

Some tools can perform integrity checks on designated files.

They have very good reporting tools usually based on HTML.

Nessus

Available from www.nessus.org Best of the scanning tools Easy to build for Linux, harder for Solaris,

need to work on other OS. Requires GNU tools Provides HTML based reports Has distributed architecture: clients

(Windows, Unix) & engines (Unix only)

Nessus – Building It

Linux– Download the RPMs– Add nessus user– Start up nessusd daemon– Start up nessus client– Start testing

Nessus – Pros/Con

Pro– Easy to install if you have linux– Most comprehensive tests for your money

Con– Not that easy to understand at first– Non-linux builds require GNU software– Some inconsistency in quality of checks– Must use Unix server for specific user accounts

X

SAINT

Based on SATAN, developed by World Wide Security, Inc. (www.wwdsi.com)

Security Administrator’s Integrated Network Tool – Gathers info on remote hosts/nets– Looks at finger, NFS, NIS, ftp, tftp, rexd, statd– Can run heavy, moderate or light probes on targets.

Will check for the SANS Top 10 Threats

SARA

Security Auditor’s Research Assistant– www.www-arc.com/sara

Checks for SANS Top 10 Threats Does Unix/Windows vulnerability tests Has CVE dictionary support Search engine for post audit analysis Has a Report Writer

Port Scanning Tools

Strobe was one of the earliest port scanning tools.– Available from ciac.llnl.gov

Nmap is the more sophisticated grandson of strobe– Available from www.insecure.org

Tripwire

Available from www.tripwire.com First of the file integrity checkers Unix and NT versions available

– Network capable versions available Academic version is free. Commercial and

NT versions are not. Useful in finding trojan programs

Tripwire

Generates a “signature” for each file based on checksums and other characteristics.

These signatures are stored in a database file that should be kept offline.

This is the baseline. Latest threat involves dynamic exec

redirection. This is part of the newer Kernel Module Rootkits.

Tripwire

List of files to check: tw.config– All files in a directory will be checked.– Can prune directories from the check step.– Can examine just the directory and nothing

else.– Can check by access time but not recommended

since you’ll get a report of everything that changed. Everything!

Tripwire

To initialize the DB: tripwire –initialize Update DB interactively:

tripwire -interactive Non-interactive DB update:

tripwire – update <FN>

Tripwire

Security Issues– Need to protect the DB– Need to protect the vulnerable executables

Advantages– Simple interface, good choice of crypto hash functions,

good all-around tool Disadvantages

– Kernel mod attacks, initial tw.config takes some time to customize, NT version is good but costs $$$, no network security

Personal Firewall Tools

These tools monitor connection attempts to your system and give you the option of allowing or denying the access

They log the connection attempt to standard log files

More valuable than real Firewall, IMHO.

Portsentry/TCP Wrappers

Available from www.psionic.com TCP Wrappers available from ciac.llnl.gov and a

ton of other sites Any host that scans a list of “banned” ports is

placed in an /etc/hosts.deny file Need TCP Wrappers installed on the machine

– Tcpwrappers logs attempts to connect to services

TCP Wrappers

Everyone should buy Wietse Venema dinner for writing this tool.

Purpose– Log network connections to a system– Allow you to filter who connects to the system

Needs an inetd-like program to act as the dispatcher of network services

TCP Wrappers Features

Allows you to monitor/filter incoming requests for SYSTAT, FINGER, FTP, TELNET, R-Commands, TFTP, TALK and other network services.

Provides access control to restrict what systems connect to what network daemons.

Provides some protection from host spoofing

TCP Wrapper Installation

Easy to do “Advanced Installation” easier than “Easy

Installation” IMHO Install done by Makefile

– make <os-type> Creates 5 modules that are ready to use.

TCP Wrappers

4 components– Tcpd – the actual wrapper program– Tcpdmatch, tcpdchk – ACL testing programs– Try-from – tests host lookup function– Safe-finger – a better version of finger

Logs hostname, IP address and username (identd if possible) via syslog facility. Typically, it logs to the mail facility logs

Change this by editing Makefile:– FACILITY=LOG_AUTH– FACILITY=LOG_WARN

TCP Wrappers

Access Control is enabled by default. 2 files

– /etc/hosts.deny – restrict access if IP addr here– /etc/hosts.allow – allow access if IP addr here

• Can restrict to username@host if services are enabled

Reverse lookup is done. Paranoid selection terminates the connection immediately if there’s a mismatch.

Set KILL_IP_OPTIONS in Makefile to refuse connections that use source routing. This prevents IP spoofing although your routers should do this.

TCP Wrappers

IDENT service– Remote username lookup required remote host to run

ident (RFC 1413) protocol.

– Works only for TCP not UDP Limitations

– TCP – checks the 1st connection for each instance of the daemon

– UDP – 1st datagram only for the service

– RPC/TCP – no checking since portmapper does this.

TCP Wrappers

Advantages– Logs and applies access controls to remote connections

– Lets you define which daemons are wrapped

– Does good reverse lookup on hosts Disadvantages

– Ident service not reliable

– Only looks at network daemons spawned by inetd

– Doesn’t wrap ALL services (RPC)

– Could give a false sense of security

Portsentry

Available from www.psionic.com Monitors ports and performs an action

when an attempt to access the port is made. Usually access is denied to the probing

systems. Monitors TCP and UDP traffic. A little

more flexible than TCP Wrappers

Portsentry Configuration Files

Portsentry.conf contains the list of ports to be monitored.

3 levels of paranoia

IP Filter

Software package that can do NAT or basic firewall services.

Designed to be used as a loadable kernel module but can be incorporated into a Unix kernel

Can be configured to do IP Accounting (count # bytes), IP Filtering or IP authentication or NAT.

http://coombs.anu.edu.au/~avalon/ip-filter.html

IP Filter

Can explicitly allow/deny any packet. Distinguishes between multiple interfaces. Filters by IP network, hosts or protocol. Filters by port number or port range. Logs the following:

– TCP/UDP/ICMP/IP packet headers– First 128 bytes– Pass or blocked status

IP Filter

Statistics collected include:– Packets blocked– Packets used for accounting (packet count)– Packets passed– Packets logged– Inbound/outbound packet information

IP Filter Log Format

Jul 30 01:46:52 myhost.vt.edu ipmon[147]: [ID 702911local0.warning] 01:46:52.196772 hme0 @0:5 b 194.143.66.126,21 ->198.82.255.255,21 PR tcp len 20 40 -S IN



Logcheck

Available from www.psionic.com Syslog keyword scanner When it matches something, it does

something– Send email– Page someone– Run a command

logcheck.violations

These keywords denote a problem and are flagged bylogcheck.

logcheck.ignore

Phrases listed in this file are ignored by the logcheck program.

logcheck.hacking

Keywords in this file indicatean attack is taking place

Zone Alarm

Available from www.zonelabs.com Not quite free Client based, application level firewall Designed to prevent unauthorized sending

and receiving of packets to your workstation

Good defense against trojans

Basic Installation Steps

The following steps were developed by Marc Debonis for our site.– Download latest version from http://www.zonelabs.com– Run the installer, zonealarm.exe– Click Next, click Next– Enter name, company and email (can be invalid)– Uncheck both boxes– Click Next , click next, click finish, click start– Check “don’t show this message again” box– Click OK and reboot if necessary– Zone Alarm is installed

Configuring Zone Alarm

ZA requires you authorize each & every application that attempts to send receive information to/from your network connection.

Default is BLOCK. This pops up a window asking what to do

Basic Setup

Click the arrow in ZA box that points down and to the right

Click the security button Verify local security is set to MEDIUM Verify internet security is set to HIGH Click the advanced button Do NOT put a checkmark next to your adapter, OW,

all machines in your subnet will be considered to be in your local zone

Click OK

Black Ice Defender

Available from www.networkice.com Workstation Version

– End-user PC with a single connection– Tuned for common attacks to workstations

Server Version– Additional NT and W2K attacks signatures

IcePac Suite allows multiple agents to be managed from a single host. Can install agents remotely.

Not quite free

NeoWatch

Available from www.neoworx.com Another Personal FW type tool for Windows

systems. Does traceback to the originating site. Similar features as Zone Alarm and Black Ice

Defender Can send data to a central site. Not quite Free $39.95. Trial version is free for

30 days

Sniffers: snoop, iptrace, tcpdump, snort

Some systems have builtin sniffers– Solaris - snoop– AIX - iptrace– Linux - tcpdump– NT/2000 - netwatch

Tcpdump is the generic sniffer for those systems with no builtin sniffer

Sniffer Output - Solaris Snoop1042 0.10594 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 login:1045 0.02429 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=67541046 0.02039 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=67541047 0.03137 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541050 0.09288 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=67541052 1.17258 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 b1053 0.08960 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 b1054 0.10377 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=67541055 0.08251 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 r1056 0.04324 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 r1087 0.24398 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 e1090 0.01475 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 e1093 0.07074 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 a1094 0.11020 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 a1105 0.07212 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754 Password:1108 0.02244 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=67541115 0.24651 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 p1120 0.07970 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541122 0.00623 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 o1123 0.11307 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541124 0.09368 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 o1125 0.10588 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541126 0.08829 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 h1127 0.13538 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541128 0.10856 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 b1131 0.04106 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=67541133 0.16857 cesgi1.ce.vt.edu -> scws29.harvard.edu TELNET C port=6754 e1136 0.02925 scws29.harvard.edu -> cesgi1.ce.vt.edu TELNET R port=6754

Tcpdump Example

Big Brother

Web based system and network monitor Client server model

– Clients run on the systems you want to monitor– Simple shell scripts that monitor different

aspects of your system and network What can it check?

– Disk space, CPU Utilization, critical processes, weather parameters, building monitors

Big Brother

Color coded WWW page showing a matrix of machines and monitored functions

Notifies sysadmins by email, pager, SMS. System requirements

– Unix – www server, /bin/sh, C compiler to port BB

– NT – v4.0 with SP3 minimum, Intel or Alpha platforms.

Big Brother

Installation Steps– cd install– ./bbconfig– cd ../src– Make– Make install– cd ../etc

• Edit bb-hosts, bbdef.sh, bbwarnrules.cfg

– cd ..– ./runbb.sh start

Big Brother

Can monitor more service by modifying bb-network.sh

BB shows historical data. Drilling down a host page and clicking on the history buttons shows the last 24 hr stats.

Doesn’t need to run as root. Run as ‘bb’. Restricts incoming connections by ACL.

VNCViewer

Available from www.uk.research.att.com/vnc Great remote control tool for Windows 95/98,

NT, 2000, Macintosh, Unix clients Nice help desk tool It displays the remote desktop on your

system. A better version of BackOrifice, BO2K tool

Lsof, inzider

These programs list the processes running on a system.

They also list the files opened by those processes.

Useful in finding where a sniffer log file is located

Sample lsof Utility Output# ./lsof /sbin/racket.udpCOMMAND PID USER FD TYPE DEVICE SIZE/OFF INODE NAMEracket.ud 450 root txt VREG 128, 16 20332 15836 /sbin/racket.

# . /lsof -p 450COMMAND PID USER FD TYPE DEVICE SIZE/OFF INODE NAMEracket.ud 450 root cwd VDIR 128, 16 1024 2 /racket.ud 450 root txt VREG 128, 16 20332 15836 /sbin/racket.udpracket.ud 450 root txt VREG 128, 16 1483100 904 /lib/libc.so.1racket.ud 450 root txt VREG 128, 16 585876 2051 /lib/rldracket.ud 450 root 3u inet 0x8af730e4 0t0 TCP *:3038

# ./lsof -p 1423,1424COMMAND PID USER FD TYPE DEVICE SIZE/OFF INODE NAMEracket.ud 1423 root cwd VDIR 128, 16 1024 2 /racket.ud 1423 root txt VREG 128, 16 20332 15836 /sbin/racket.udpracket.ud 1423 root txt VREG 128, 16 1483100 904 /lib/libc.so.1racket.ud 1423 root txt VREG 128, 16 585876 2051 /lib/rldracket.ud 1423 root 0u inet 0x89c804e0 0t373 TCPcesgi1.ce.vt.edu:3038->sable.cc.vt.edu:4894racket.ud 1423 root 1u inet 0x8a8d8d60 0t225 TCPcesgi1.ce.vt.edu:1307->vtaix.cc.vt.edu:telnetracket.ud 1424 root cwd VDIR 128, 16 1024 2 /racket.ud 1424 root txt VREG 128, 16 20332 15836 /sbin/racket.udpracket.ud 1424 root txt VREG 128, 16 1483100 904 /lib/libc.so.1racket.ud 1424 root txt VREG 128, 16 585876 2051 /lib/rldracket.ud 1424 root 3u inet 0x8af730e4 0t0 TCP *:

Sysadmin Tools

Sudo – Unix access control is all (root) or nothing

(user).– Some commands (backup, restore) are

restricted to root but are really an OPER class command. You don’t want an operator to have root access but you want them to do backups.

– Sudo lets you set up this “pseudo” privilege scheme.

Sudo

Sudo uses user identity and host to restrict the commands the user can run in “root” mode.

It is a restricted root shell. User is prompted for a special password

that allows them to run the command.

Sudo

The sudoers files lists the commands, shells, hosts that a user can execute commands

Should always list the full path name for the commands

Notifies sysadmins if illegal uses of sudo is attempted.

Notifies sysadmins if user in sudoers tries to run a restricted command

Sudo

Advantages– Good warning if someone tries to use it incorrectly.– Easy to configure for multiple machines– Adequate internal security checks

• Check for “.” in PATH• Removes LD* variables before execution

Disadvantages– Works with root userid only. Can’t use with other

userids.– Doesn’t handle commands that use a subshell to spawn

other commands

Proactive Password Tools

Most newer OS allow you to set password rules in config files.

Crack is still the best of the bunch. Npasswd and passwd+ are two older but still

effective tools. Npasswd is a good tool for those who don’t want

to spend a lot of time configuring a password checker

Passwd+ requires more configuration time.

Crack

The first of the really good password crackers. Available on the net for the past 10 years.

Easy to customize. Works on non-shadow password files.

Use a preprocessor to rebuild in old format or use NIS, NIS+

Can be distributed among systems http;//www.users.dircon.co.uk/~crypto/

npasswd

Uses ASCII dictionaries or DBM format dictionaries. Programs to build directories included. If the password is in the dictionary, it’s rejected. Case

and reversed word checks are done as well Does singlecase (Yes/No) checks

– Allow passwords in one case. Default = No. Does Control Character (Yes/No) checks.

– Allows passwords with ASCII control characters in them. Default = Yes.

Does min/max length checks.

npasswd

Checks for 3 sequential occurrences of the same character. This value can be modified.

Does illegal character check. (^C, ^D, ^G, ^J, ^M, ^O, ^Q, etc.

Good, quick easy tool to use.

Home Grown Tools

Network Mgt Group developed a couple of tools for their use.

Our CIRT can use the same tools to track an attack in our network.

Our Netadmins controls the ENTIRE University net and developed these tools to help them manage, fix and bill usage of net resources. SQL front ends to Oracle DB.

Using the Tools – A Strategy

Preparation Detection Containment Eradication Recovery Followup

Preparation

Unix Host Systems– Install TCP Wrappers, Portsentry, logcheck,

tripwire, lsof, ipfilter NT/2000

– Inzider,syslog converters Network

– Ingress, egress filters in place– Router logs in place

Detection

Portsentry, TCP wrappers, Personal Firewall tools usually send the first alarm.

Network router filters may trigger an alarm as well.

Once an event is detected, reaction mechanisms are enabled

Containment

Detection tools give the source IP address. Router blocks may be enabled to prevent

additional attacks. HC++ tool used to isolate offending system Portsentry or PFW tools prevent further

access to the systems

Eradication

HC++ tool used to shut off internal port. Router blocks on external IP address. Tripwire used to remove offending files. Network backup software can be used to

verify this. Why? Most network backup software does incremental backups so they can capture a newly installed file.

Recovery

“Jumpstart” style OS installation Network and regular backup software File servers may limit the damage

Followup

See what components worked.– Could additional scanning detect the holes?– How fast did the reaction mechanisms work?– Internal network tools work?– Backup procedures work?– What didn’t work? Why? How?

Summary

There are some excellent freeware tools that will help you with sysadmin and security issues at your site.

Use these tools to gain experience in evaluating vendor tools.

A combination of vendor and freeware tools is desired

There are MORE tools out there.

Where to Get the Tools

Http://ciac.llnl.gov– TCP Wrappers, crack, tcpdump, lsof

Http://www.wwdsi.com– SAINT

Http://www.www-arc.com/sara– SARA

Http://www.tripwire.com– tripwire


Http://www.psionic.com– Logcheck, portsentry

Http://www.uk.research.att.com/vnc– VNCViewer

Http://www.insecure.org– Nmap

Http://www.ssh.org– SSH


www.nessus.org– Nessus

http://packetstorm.securify.com (now defunct)

Documents

Building a Secure Environment for Free