Using OSSEC Open Source Host based IDS/IPS

Using OSSEC Open Source Host
Based Intrusion Detection
Justin C. Klein Keane
University of Pennsylvania
School of Arts & Sciences
Information Security and Unix Systems
©Justin C. Klein Keane
<jukeane@sas.upenn.edu>

Presentation Format
 Top down
- High level definition
- Capabilities
- Customization
- Our Implementation
- Logistics

Network vs. App Security
• We've won network security
• Made it more expensive to compromise
networks than applications
• Defending applications requires new
approaches
• OSSEC fits easily and naturally into an
application security program

About OSSEC
 Open source host based intrusion detection
system (HIDS)
 Written by Daniel Cid, who continues to
participate
 Pronunciation varies
 Acquired by Third Brigade in 2008, which was
then acquired by Trend Micro in 2009

What is an IDS
 Intrusion detection system (IDS)
 Distinct from an intrusion prevention system
(IPS)
 Monitor data points to identify malicious
behaviour
 Anomaly detection or pattern matching
 Basically just automated traffic monitoring

Differences of HIDS vs. NIDS
 HIDS – host based IDS
 NIDS – network based IDS
 NIDS uses data from the wire
 HIDS can use filesystem as well as network
– Log files, file contents
– Filesystem attributes
 Main difference: visibility

Advantages of HIDS
 Low(er) false positive rate
 If your HIDS detected the traffic it was
definitely parsed by the target
 Leverages existing hardware
 Not very resource intensive

Disadvantages of HIDS
 Blind spots:
 If it isn't logged, or stored on the filesystem,
it's invisible
 Unable to parse unknown or unlogged traffic
 Can't evaluate egress
 Can't spot probes that don't hit active services
 Requires an agent install on endpoints
 Can be defeated with a host compromise

Advantages of NIDS
 All traffic becomes visible, ingress and egress
 Requires just one point of installation
 Failure doesn't affect endpoints

Disadvantages of NIDS
 High false positive rate
 No way to tell if attack was “real”
 Easy to overwhelm with bad traffic or evade
– Packet fragmentation, etc.
 Can't see encrypted traffic

OSSEC Beyond HIDS
Filesystem integrity checking
Registry monitoring on Windows
Active response
Commonly used for RTBL
Can be scripted for almost any behaviour
Rootkit detection

Why Penn is Using OSSEC
• Found OSSEC in a search for open source
SEM and SIM solutions
• No access to network taps or span ports
• Looking for a sensor net to correlate alerts
• Using OSSEC for over 3 years now

How OSSEC Works
Three modes
Local, client, server
Client server model
Clients receive configuration from server
Clients send logs to server over an encrypted channel

OSSEC Network Communication
• UDP port 1514
• Compressed messages (using zlib)
• Blowfish based encryption using pre-shared
keys
• Logs specified on client are collected and sent
to manager for analysis

OSSEC Data Flow
Graphic concept courtesy http://ossec.net/ossec-docs/auscert-2007-dcid.pdf

OSSEC Decoders
• OSSEC uses decoders to parse log files
• Decoders are written as XML
• Extracts useful data fields from log entries to
use for rule and alert matching including:
– Source IP and/or port
– Destination IP and/or port
– Program name or user name
– And more...

OSSEC Rules
• OSSEC rules are stored as XML files
• Rules are hierarchical
• By default OSSEC includes rules for:
apache, arpwatch, asterisk, cisco-ios, courier, firewalls,
ftpd, horde/imp, IDS systems, IMAP, McAfee antivirus,
MS auth, MS DHCP, Exchange, Microsoft FTPD,
MySQL, Bind, Netscreen, PAM, postfix, Postgres,
ProFTP, Roundcube, sendmail, samba, Squit, SSH,
Symantec AV, Syslog, Telnet, VMWare, VSFTP,
Wordpress, and more...

Rule Format
 Rules are assigned priority levels, usually from 1
(lowest) to 15
 Rules trigger based on:
- Pattern matching in strings
- Timing between matches
- Dependence on other rules
- Time of day
- Hostnames
- Applications

OSSEC Alerts
• Default settings include alerting on:
– Web attacks
– SSH brute force
– Buffer overflows and program crashes
– Firewall events
– Users using sudo
– Many more...
• Creating custom alerts is relatively easy

Alert Behavior
• When a rule triggers an alert several actions
can be configured:
– Logging
– Sending an e-mail alert
• Sending a SMS alert
– Executing an active response script

Active Response
 Initiates scripts
 Default installations include firewall rules
- Time based
 Whitelists prevent self denial of service
 Active response can be delegated to multiple
hosts

Custom Decoders and Logs
• OSSEC will monitor many common services
out of the box
• OSSEC can be extended to monitor custom
applications
• OSSEC can detect events in custom
application logs and trigger custom active
response scripts

Log File Monitoring
• OSSEC monitors specific logs by default,
including:
– Syslog
– Apache http logs
– Mail logs
• OSSEC can be configured to monitor any log
it can gain access to

Beyond HIDS: Monitoring Scripts
• OSSEC can be used to monitor the output of
custom scripts
• For instance, OSSEC can generate alerts
based on changes to NMAP scan results of
specific hosts
– http://www.ossec.net/wiki/Know_How:Nmap
• Can also log scripted alerts to common log
(syslog) and write a rule to augment existing
log monitoring

Generating Reports
 OSSEC includes ossec-reportd
- Can be used to generate summary reports
- Ex. show all brute force attempts and usernames
used and number of times attempted
 OSSEC can also log to a database so that SQL
can be used for reporting
 Custom scripts can be used to parse alert logs
 Web based user interface (WUI) reporting

OSSEC Community
 Extremely active user community
- Developer mailing list
 OSSEC mailing list (and Google group)
- http://groups.google.com/group/ossec-list
 OSSEC wiki
- http://www.ossec.net/wiki
 Commercial support from Trend Micro
- ossec.purchase@trendmicro.com

Solutions
• OSSEC is a service you can utilize internally
or offer your stakeholders
• OSSEC allows you to extend your security
impact
• OSSEC provide you greater visibility into your
security posture

How Penn is Using OSSEC
• Server installed on a bastion host
• Agents deployed on critical hosts
• Separate server installed on cluster back ends
• Alerts go to queue monitored by security staff
• Per machine alerts go to individual sysadmins
• Using OSSEC to monitor custom alert scripts

Logistical Considerations
• As with any intrusion detection system, expect
a timeframe for tuning
• Be extremely careful with active response to
avoid self denial of service
• Installation may require coordination with
sysadmins

Overall Impact
• Develop metrics to justify security resource
allocation
• Verify effectiveness of security
countermeasures
• Track outlying machines, especially virtual
machines
• Extend service offerings to client groups
• Centralized log reporting

Pitfalls of OSSEC
• Difficulty in upgrades between versions
• Coordinating pre-shared keys can be
problematic
• Sometimes agents become unresponsive
• Volume of alerts
• In testing OSSEC is great for early warning
but not so good in a post compromise situation

Questions
Thank you.

Using OSSEC Open Source Host based IDS/IPS

More Related Content

Similar to Using OSSEC Open Source Host based IDS/IPS

Recently uploaded

Using OSSEC Open Source Host based IDS/IPS