copyright 2001 marchany1 auditing networks, perimeters and systems unit 5: audit checklist using cis...
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Copyright 2001 Marchany 1
Auditing Networks, Perimeters and Systems
Unit 5: Audit Checklist using
CIS Rulers: Procedural, Perimeter, and UNIX
The SANS Institute
Copyright 2001 Marchany 2
Applying TBS to the real world!
Top Ten Vulnerabilities, the vulnerabilities responsible for most hacks
Apply TBS as an approach to an effective understandable security policy– Basics– Perimeter– Unix– NT– Windows 2000
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The TBS Audit Layers
A complete IT audit is a set of component audits. You should be able to measure E, D and R times for each layer of the security architecture.
Components– Procedural: E = D+R– Perimeter(Firewall): E = D+R– UNIX: E = D+R– NT/Windows 2000: E =D+R
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CIS Rulers Rulers list a set of minimal actions that need to be
done on a host system. This is a consensus list derived from security
checklists provided by CIS charter members (VISA, IIA, ISACA, First Union, Pitney Bowes, Allstate Insurance, DOJ, Chevron, Shell Oil, VA Tech, Stanford, Catepillar, Pacific Gas & Electric, RCMP, DOD CIRT, Lucent, Edu Testing Services and others)
Can’t develop your own set? Use these! http://www.cisecurity.org
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CIS Rulers: A Security and Audit Checklist Level 1
– Mandatory Actions required regardless of the host’s location or function.
Level 2– Dependent on your network topology– Different for switched nets vs. shared nets vs.
wireless nets, etc.
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CIS Rulers: Security Checklist & Audit Plan Level 3
– Application Specific (WWW, FTP, DB, Auth)
Procedural– Examines the policies in place.– This is the policy review checklist.
FTP WWW DB MailSwitched Wireless Non Switched
LEVEL 1
Level 3Level 2
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CIS Rulers: Procedural
General Administration Policies Key security tool installed User Accounts and environment System Logs Network File sharing General Email Issues This review is done during the Audit
Planning Phase of the audit process
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CIS Ruler: Procedural
General Administration Policies– Acceptable Use Policy
– Backup Policy
– Security Administrator duties
– Whois Contact Information (Tech/Admin)
– System changelogs (Source Revision Control)
– Incident Response
– Minimum software requirements
– User, temp, system account policies
– Patches
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CIS Ruler Example: Backups
· Does a backup policy exist?· Do backup logs exist?· What data is backed up· How often data is backed up· Type of backup (full, differential, etc.)· How the backups are scheduled and verified· How the backup media is handled and labeled· How the backup media is stored· How long the backup media is retained· How backup media is rotated and expired· How backup data is recovered
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CIS Ruler: Procedural
Key security tools installed– Network routers implement minimum filtering
requirements– Verify network routers are properly configured
and monitored for in/out traffic– Are all firewalls properly configured and
monitored for in/out traffic– The above rules prevent DDOS attacks from
affecting other nets.
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CIS Ruler: Procedural
User Accounts and Environment– Remove obsolete user entries from system
System Logs– How long are they kept? Are they secured?
Network file sharing– Review what filesystems this system can access– Review what filesystems this system exports
Email Policy– Abuse Policy?
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CIS Ruler: Written Documentation and Policies
Where is it? Is it available to anyone that needs it? Is it up to date? Is anything major missing (SGI policies, but
no HP policies)?
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CIS Ruler Example: Security Policy
Purpose - the reason for the policy. Related documents – lists any documents (or other policy) that affect the contents of this
policy. Cancellation - identifies any existing policy that is cancelled when this policy becomes
effective. Background - provides amplifying information on the need for the policy. Scope - states the range of coverage for the policy (to whom or what does the policy
apply?). Policy statement - identifies the actual guiding principles or what is to be done. The
statements are designed to influence and determine decisions and actions within the scope of coverage. The statements should be prudent, expedient, and/or advantageous to the organization.
Action - specifies what actions are necessary and when they are to be accomplished. Responsibility - states who is responsible for what. Subsections might identify who will
develop additional detailed guidance and when the policy will be reviewed and updated.
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Procedural: Incident Response Plan Are the six Incident Response steps covered?
– Preparation
– Identification
– Containment
– Eradication
– Recovery
– Lessons Learned (if there are no lessons learned documents either the plan isn’t followed or no incidents have occurred).
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Procedural: Training & Education Do technical people have the training to do
their job competently? Are there standards their skills can be
measured against? Are there standards of compliance that
ensure they are using their training in accordance with policy?
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Procedural: Physical Security
Consoles in physically secure areas? Fire suppression? Backups? Offsite backups? Network components secured? Phone wiring secured?
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Procedural: Windows 2000
These are based on the SANS “Securing Windows 2000” booklet.
Least Privilege Principle Avoid granting unnecessary Admin privs. Limit Domain Trust. Restrict modems in workstations and servers. Limit access to sniffer software (Network
Monitor).
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Procedural: Windows 2000 Keep system software updated. Update and Practice a Recovery Plan. Require strong passwords. Require password protected screen savers. Establish Auditing and Review Policies. Require Administrators to have a User and
Administrator account. Require antivirus software. Install host based IDS. Perform periodical low-level security audits.
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CIS Procedural Ruler Review
Procedural rulers give you a starting point for determining your site’s policy pie
These policies include acceptable use, privacy, incident response, accountability, backup and any other appropriate action
The CIS procedural ruler is a consensus list of practices done at the charter members sites.
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CIS Level 1 Ruler: Unix
Patches Key Security Tools Installed System Access, authentication,
authorization User Accounts and Environment Kernel Level TCP/IP tuning Kernel Tuning
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CIS Level 1 Ruler: Unix
Batch Utilities: at/cron UMASK issues File/Directory Permissions/Access System Logging SSH Minimize network services
Copyright 2001 Marchany 24
CIS Level 1 Ruler: Unix
Minimize RPC network services Minimize standalone network services General Email Issues X11/CDE General Administration Policies Specific Servers
– www, ftp, DB, Mail, NFS, Directory, Print, Syslog
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CIS Level 1 Unix Ruler - Patches Define a regular procedure for checking,
assessing, testing and applying the latest vendor recommended and security patches.
Keep 3rd party application patches updated. Why?
– The first line of defense is proper patch/Service Pack installation.
– Patches are living and need to be updated regularly
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CIS Level 1 Unix Ruler: Security Tools These tools help decrease your detection
time, D Install the latest version of TCP Wrappers on
appropriate network services SSH for login, file copy and X11 encryption Install crypto file signature function to
monitor changes in critical system binaries and config files (tripwire)
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CIS Level 1 Unix Ruler: Security Tools Install Portsentry or similar personal FW
software Run NTP or some other time sync tool Run “logcheck” or similar syslog analysis
or monitoring tool Install the latest version of sudo
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CIS Level 1 Unix Ruler: Access, Authorization No trusted hosts features: .rhosts, .shosts
or /etc/hosts.equiv Create appropriate banner for any network
interactive service Restrict direct root login to system console Verify shadow password file format is used Verify PAM configuration
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CIS Level 1 Unix Ruler: Kernel-Level TCP/IP Tuning System handling of ICMP packets is
secured System handling of source routed packets
secured System handling of broadcast packets
secured Use strong TCP Initial Sequence Numbers Harden against TCP SYN Flood attacks
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CIS Level 1 Unix Ruler: Kernel Level Tuning, Batch Utilities Enable kernel level auditing Enable stack protection Ensure ulimits are defined in /etc/profile
and /etc/.login Restrict batch file access to authorized users Ensure cron files only readable by root or
cron user
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CIS Level 1 Unix Ruler: UMASK, File Perms, Access
Set daemon umask to 022 or stricter Set user default umask (022 or 027) Console EEPROM password enabled? Check /dev entries for sane ownership and
permissions Mount all filesystems RO or NOSUID All filesystems except / mounted NODEV
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CIS Level 1 Unix Ruler: File Perms and Access Verify passwd, group, shadow file perms Verify SUID, SGID system binaries Disable SUID, SGID on binaries only used
by root No World-write dirs in root’s search path Sticky bit set on all temp directories No NIS/NIS+ features in passwd or group
files if NIS/NIS+ is disabled
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See what we can find
/usr/bin/find / -local -type f -name '.rhosts' -exec ls -al {} \; -exec cat {} \; 2 (.rhosts)
/usr/bin/find / -local -type f -user root -perm -4000 -exec ls -dal {} \; 2 (SUID files) /usr/bin/find / -local -type f -user root -perm -2000 -exec ls -dal {} \; 2 (SGID files)
find /\(-local –o –prune\) -perm –000002 –print
find /name .netrc -print
find / -perm –1000
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Audit Report ExampleAudit MethodLs –la (list files) against critical files to determine their permissionsFindingSeveral system configuration files in /etc are writableRisk Level: High
Security Implication The /etc directory is critical for establishing the operating configuration of many system services including startup and shutdown. If an attacker is able to modify these files, it may be possible to subvert privileged operating system commands.
Recommendation Change permissions of all files in /etc to be writable by root or bin only.
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/dev Permissions Exhibit# ls –l /devtotal 72-rwxr-xr-x 1 root root 26450 Sep 24 1999 MAKEDEVcrw------- 1 root sys 14, 4 Apr 17 1999 audiocrw------- 1 root sys 14, 20 Apr 17 1999 audio1brw-rw---- 1 root disk 32, 0 May 5 1998 cm206cdcrw--w--w- 1 root root 5, 1 May 26 15:17 consolebrw------- 1 root floppy 2, 1 May 5 1998 fd1brw-rw---- 1 root disk 16, 0 May 5 1998 gscdbrw-rw---- 1 root disk 3, 0 May 5 1998 hdabrw-rw---- 1 root disk 3, 1 May 5 1998 hda1brw-rw---- 1 root disk 3, 10 May 5 1998 hda10brw-rw---- 1 root disk 3, 11 May 5 1998 hda11brw-rw---- 1 root disk 3, 12 May 5 1998 hda12brw-rw---- 1 root disk 3, 13 May 5 1998 hda13brw-rw---- 1 root disk 3, 14 May 5 1998 hda14brw-rw---- 1 root disk 3, 15 May 5 1998 hda15brw-rw---- 1 root disk 3, 16 May 5 1998 hda16
Copyright 2001 Marchany 36
World-Writeable and SUID/SGID Files
Audit MethodFind commands were executed on the servers to locate all files with world-writeable permissions and SUID/SGID permissions. The output was redirected to appropriate files for later analysis. FindingA large number of world-writeable and SUID/SGID files were found on the server XYZ. Further, a number of files in the /usr, /opt and /var directories allow all users to have write permission. Security Implication World-writeable files allow any user or an intruder to change the contents of a file, effecting information integrity. Also, for executable files, an intruder may replace the file with a trojan horse that can damage the system and its integrity. SUID/SGID files execute with the privilege of the owner/group. These can be subverted by an unauthorized user or intruder to escalate their privilege to those of the owner/group of the SUID/SGID file. Risk Level: High Recommendation Review all world-writeable and SUID/SGID files on the system. Using freeware tools like fix-modes or YASSP can facilitate identifying and correcting the permissions on files. After the review, create a list of all the remaining “approved” World-writeable and SUID/SGID files on the system and store in a secure place. Periodically, check the system against this list to identify changes and ensure that such changes are approved. NFS shared files, especially files in /usr, /opt and /var should be exported ‘read-only to specific hosts. Further, through /etc/vfstab, the exported file systems (except special cases like /tmp, /dev and /) should be mounted with the nosuid option to prevent the inadvertent granting of SUID privilege on NFS mounted files.
Copyright 2001 Marchany 37
CIS Level 1 Unix Ruler: System Logging and SSH Capture messages sent to syslog AUTH
facility (enable system logging) Copy syslogs to central syslog server Audit failed logins and SU attempts Enable system accounting Logins allowed via SSH only (no rsh,
rlogin, ftp or telnet)
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CIS Level 1 Unix Ruler: Reduce Services (/etc/inetd.conf) Disable name (UDP) Disable exec/rexec (TCP) Disable login/rlogin (TCP) Disable uucp (TCP) Disable systat (TCP) Disable netstat (TCP) Disable time (TCP/UDP)
Copyright 2001 Marchany 39
CIS Level 1 Unix Ruler: Reduce Net Services (/etc/inetd.conf) Disable echo (TCP) Disable discard (TCP/UDP) Disable daytime (TCP/UDP) Disable chargen (TCP/UDP) Disable rusersd (RPC) Disable sprayd (RPC) Disable rwall (RPC)
Copyright 2001 Marchany 40
CIS Level 1 Ruler: Reduce Net Services (/etc/inetd.conf) Disable rstatd (RPC) Disable rexd (RPC) Use TCP Wrappers for all enabled network
services (TCP/UDP)
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Sample /etc/inetd.conf
# Shell, login, exec, comsat and talk are BSD protocols.
#
shell stream tcp nowait root /usr/sbin/tcpd in.rshd
login stream tcp nowait root /usr/sbin/tcpd in.rlogind
#exec stream tcp nowait root /usr/sbin/tcpd in.rexecd
#comsat dgram udp wait root /usr/sbin/tcpd in.comsat
talk dgram udp wait nobody.tty /usr/sbin/tcpd in.talkd
ntalk dgram udp wait nobody.tty /usr/sbin/tcpd in.ntalkd
This is a fragment of /etc/inetd.conf where shell, login, talk, and ntalk probably should be commented out. Note the /usr/sbin/tcpd so this system is probably running tcpwrappers. More of the file is in the notes pages.
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Output ExampleFingerd running
Audit MethodTelnet localhost 79 to connect with the local system’s finger daemon FindingFingerd is active Risk Level: Low
Security Implication Finger can be used to gain reconnaissance information about the system including the last login time, where a user is logged in from, information about their shell. This information could be used to set up either a social engineering or trust model based attack.
Recommendation If finger is not a business critical application in this environment, disable finger or replace with free tools such as sfinger.
Copyright 2001 Marchany 43
CIS Level 1 Unix Ruler: Reduce RPC Network Services Restrict NFS client request to originate
from privileged ports No filesystem should be exported with root
access Export list restricted to specific range of
addresses Export RO if possible Export NOSUID if possible
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CIS Level 1 Unix Ruler: Email, X11/CDE Use Sendmail v8.9.3 or later. (v8.11.4 is
current 6/15/01) Restrict sendmail ‘prog’ mailer Verify privileged and checksums for mail
programs Ensure X server is started with Xauth Use SSH to access X programs on remote
hosts
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CIS Level 1 Unix Ruler: User Accts, Environment Enforce strong passwords No null passwords Remove root equivalent users (UID=0) No “.” in root PATH No .files world or group writable Remove .netrc, .exrc, .dbxrc files User $HOME dirs should be < 755
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TBS Example Using E=D+R •Security policy: automated script to check password file for users with UID 0 (superuser access) returns user ”zippy”.
•Syslog is checked:Apr 15 21:07:59 6C: goodnhacked.com telnetd[5020]: connect from some.comApr 15 21:08:18 6E: goodnhacked.com login[5021]: [email protected] as zippy
•IDS returns:21:07:16.63 badguy.com.26617 > goodnhacked.com.5135: udp 21:07:16.66 goodnhacked.com.5135 > badguy.com.26617: udp 69
5135 is SGI Object Server with a known vulnerability
Copyright 2001 Marchany 47
CIS Level 1 Ruler Review
The previous action items should be done on any Unix system on your network regardless of its function
A similar checklist is being developed for Windows 2000.
The Level 1 rulers impose a minimum security standard on all Unix and Windows 2000 systems.
Copyright 2001 Marchany 48
CIS Level 2 Rulers
Once Level 1 rulers have been applied, you pick the appropriate Level 2 ruler.
This is very organization specific. What works at my site might not apply at yours.
Additional service may be disabled if they aren’t needed.
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CIS Level 2 Ruler: Unix
Kernel-level TCP/IP tuning Physical Console Security SSH Minimize network services Minimize RPC network services General email issues X11/CDE
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CIS Level 2 Ruler: Unix
Kernel Tuning– Network options for non-router machines– Disable multicast
Physical Console Security– Enable EEPROM password. Who knows it?
SSH– Restrictively configure it
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CIS Level 2 Ruler: Unix
Minimize Network Services– Disable inetd entirely– Disable FTP– Disable Telnet– Disable rsh/rlogin– Disable comsat– Disable talk– Disable tftp
Copyright 2001 Marchany 52
CIS Level 2 Ruler: Unix
Minimize network services– Disable tftp– Disable finger– Disable sadmin– Disable rquotad– Disable CDE Tooltalk server (ttdbserverd)– Disable RPC/UDP/TCP ufs– Disable kcms_server
Copyright 2001 Marchany 53
CIS Level 2 Ruler: Unix
Disable fontserver Disable cachefs service Disable Kerberos server Disable printer server Disable gssd Disable CDE dtspc Disable rpc.cmsd calendar server
Copyright 2001 Marchany 54
CIS Level 2 Ruler: Unix
Minimize Network Services– If FTP service is enabled, see additional level 3
requirements for FTP servers– If tftp is enabled, use the security option– If sadmind is enabled, use the security option
Copyright 2001 Marchany 55
CIS Level 2 Ruler: Unix
Minimize RPC network services– Disable NFS server– Disable Automounter– Disable NFS client services– Add ports 2049, 4045 to privileged port list– Disable NIS– Disable NIS+– Replace rpcbind with more secure version
Copyright 2001 Marchany 56
CIS Level 2 Ruler: Unix
General Email Issues– Don’t run sendmail on machines that don’t
receive mail– Remove mail aliases which send data to
programs (Vacation)
X11/CDE– Disable CDE if not needed– Use the SECURITY extension for X-Server to
restrict access
Copyright 2001 Marchany 57
CIS Level 2 Ruler Review
Level 2 rulers are site specific. They are more sensitive to vendor software
requirements. For example, a vendor product may require that you enable the dreaded r-commands. You have no choice so you keep an eye on that vulnerability.
They may impose stricter standards.
Copyright 2001 Marchany 58
CIS Level 3 Ruler Example: Perimeter Defense Scope of Impact – The whole site Probability of Impact – 100% if connected
to the Internet Wide variety of opinions Every site has a Firewall (FW) of some sort.
It may be a packet filtering router or a fancy stateful FW.
What about wireless nets?
Copyright 2001 Marchany 59
Firewalls: Where’s the Threat?
FW look to the outside for threats. Can be circumvented by wireless world. Don’t prevent internal attacks. Useless? NO! It’s a component of your layered
defense. Remember the TBS Layered Defense equations.
Personal FW software is GOOD!– Makes wireless nets more secure!
What if crimes are committed by someone inside the firewall.
Copyright 2001 Marchany 60
Firewalls require management.
Someone has to manage the firewall.– Someone has to assure that the firewall is
configured properly.– Someone has to assure that all new
applications don’t violate security policies.
– Someone has to review firewall logs.– Firewalls generate a HUGE number of
logs.
Copyright 2001 Marchany 61
Sample Firewall Ruler Firewalls are one part of a layered defense which
should include:– A properly configured border router.– A virus detection solution.– An authentication system for trust management.– Properly configured operating systems and
Internet applications. Personal FW software installed on all hosts.
– An Intrusion Detection System Firewalls require monitoring and change control
management.
Copyright 2001 Marchany 62
TBS and the PerimeterE= D + R Perimeter defenses are the an effective method of “shrinking” D and R and decreasing E.
INTERNET
ISP
E
Front EndCritical systems located on a screened subnet off ofone leg of a firewall.
FirewallDNS Email
Copyright 2001 Marchany 63
Example: D&R at the Perimeter
Oct 12 01:04:26 ucc3.edu 45725: 8w5d^I: %SEC-6-IPACCESSLOGP: list190 denied tcp 202.159.123.192(2235) -> 172.20.8.233(3128), 1 packet
Oct 12 01:10:14 ucc3.edu 45730: 8w5d^I: %SEC-6-IPACCESSLOGP: list190 denied tcp 202.159.123.192(2235) -> 172.20.8.233(3128), 3 packets
This is a log file from a Cisco router on the perimeter, it indicates the router has blocked two attempts to destination port is 3128, the SQUID Proxy. Note: “denied” implies D and R are working. The times are very small!
Copyright 2001 Marchany 64
Pulling the perimeter together
Top Ten blocking, egress filtering Additional requirements from your site’s
security policy The notes contain a minimal Perimeter
audit plan!
Top Ten recommendations are shown in notes pages. There are examples of implementations based on this security policy at: http://www.sans.org/giactc/gcfw.htm ( practicals 30 - 35)
Copyright 2001 Marchany 65
Section Review
Establishing and testing perimeter defenses is a good way to reduce D and R time.
Top Ten vulnerabilities are generally agreed to be a priority. Top Ten blocking recommendations are the foundation of a security checklist for perimeters
CVE names help ensure sysadmins and auditors are referring to the same threat
Copyright 2001 Marchany 66
CIS Unix Ruler Review
CIS Rulers are a good starting point for developing a Unix audit plan
Level 1 ruler defines minimum security standards for all Unix systems
Level 2-3 rulers are more network and function specific
Procedural rulers address policy issues