The Haystack:Monitoring Network Behavior

Alan WhineryU. Hawaii ITS

Chief Internet Engineer

What this talk is about

Admins: putting concepts in heads, tools in hands

Users: understanding how to monitor, how you can be monitored

Does Not Constitute Legal Advice You are responsible obeying the law, regardless of

what I say today! (et ignorantia juris non excusat) All readily-available information, I offer no big

secrets

Schiller's Haystack

1993: The best protection is volume of information. Your best defense is obscurity, given the size of the “Haystack”

2010: Anything that's not encrypted is no more private than what's on Facebook. Your needle needs to be disguised, so it cannot be

found. And encryption is a can of worms (outside scope)

Packet Sniffing

Any computer that's part of a network can “see” some packets on its interface to that network

With certain software, you can examine and save the packets that are “visible” to your machine's interface

Many are intimidated by the task of packet sniffing; they spend time with less capable methods and get less useful results

the broadcast domain On a switched network, each switch port will

pass only traffic that is addressed to a destination connected to that port. If your computer is connected directly to a switch

port, then it will only get packets addressed to it, or to any group of destinations that includes it

On a multiple access segment (wireless, Ethernet hub) network, all packets are repeated to all destinations, and all computers can observe packets sent by other computers

the broadcast domain Additionally, a wireless host can listen to

wireless packets, regardless of association. (this takes special effort, probably need a Unix-like (e.g. BSD, Linux) computer

The Header Train Ethernet (WiFi, Mobile)

ARP IPv4

TCP SMTP * IMAP/POP HTML * BitTorrent etc

UDP RTP * DNS Queries

ICMP Etc

Common (free) Sniffers Wireshark (tshark, et al) nee Ethereal

Common GUI-based, all platforms tcpdump

Eldest, CLI-based ngrep

Allows capture based on packet contents

Etc.

Programming libpcap

The basis for practically everything. Multi-OS compatible packet capture library, with interfaces written for most common languages

Scapy Python module; allows VERY versatile packet level

analysis and fabrication Perl Module Net::Pcap

A simple Perl script can be faster than a complex C program (like tshark, tcpdump)

Wireshark

Wireshark Frame Decode (SSDP)

Layers within a frame

Wireshark Graph of TCP Transfer

Wireshark Expert Info

Dancing with yourself

It's easy (possibly even legal) to observe your own traffic, on a single-user computer

This can show you what traffic is reaching your interface, to examine, network “noise”, attack signatures, or simply to learn about sniffing

See web cookies, see if your password is “in the clear”, see why a connection is not working

See what traffic your computer is generating,

Dancing with yourself

Wireshark: menu: Capture->Interfaces

Click “Options” next the interface with the highest packet count

Dancing with yourself

Wireshark: Capture options

Capture Filter: “ip” uncheck (…) promiscuous

Dancing with yourself

Self-sniffing pitfalls Using a packet sniffer on a host that is

participating in the traffic being sniffed may: Fail CRC checks due to CRC off-loading Have weird packet sizes due to TCP segmentation

off-loading It's usually cleaner to sniff from a non-

participant host, using packet mirroring or an optical splitter

If you want to self-sniff and create capture files for reference, change interface properties to exclude any off-loading, to be safe

Mirroring or Splitting In the 1990's, one machine on the campus FDDI

or multi-access Ethernet backbone could see all (off-LAN) traffic

Now, in the switched world, all links are point to point, and there is no way for a third point to be on a link

Packet mirroring copies packets from a link to a sniffer port (this is called a SPAN session on Cisco IOS)

On fiber links, an optical splitter can divert light to a sniffer, requiring one observing interface per direction on the sniffer

Promiscuous capture

This places the “sniffing” interface in a special mode which enables it to receive packets bound for any destination, whether the local machine would normally receive them or not

On a switched network, promiscuous is not very different from non-promiscuous– Going non-promiscuous is a way to limit “noise”

On a major link between routers, it allows an observer to see everything

Legal issues

Significant distinction between “envelope” or “header” info and “content”

Persons who are employed as network/system admins may examine “header info” as part of their jobs

Law enforcement needs court orders to obtain network info, which may include compelling provider admins to collect and filter information

Privacy Issues

Always err on the side of caution Never store traffic captures longer than their

specific purpose calls for Exposes them to subpoena “ “ “ compromise

Never share raw captures with outsiders (except authorized law enf.) Sanitize and obfuscate

Taking what you need

In doing surveys of OS types in use on our network in 2008, 2009 Learned that a small, purpose-built Perl script is

MUCH faster than a general case sniffer Able to match only the piece of packet that had

relevance to the survey and never examine or store the rest

Most sniffers offer “snap length” parameter, which allows capturing only the first so-many bytes of a packet Saves storage, excludes “content” protects privacy

Storing/Sharing Captures On a major link which carries about 40% of UH

ingress/egress traffic, capturing 2 million packets takes about 10 seconds during a weekday afternoon.

If you limit capture to 60 bytes and estimate about half of that rate average, that's 518 GB per day (8.6 billion packets/day)

In order to analyze or characterize that data, you would need separate machines with access to the data, and keeping the analysis occuring at a 1 day per day rate would require constant optimization.

Storing/Sharing Captures Sharing data outside the group of people who

have a legal justification to access it is risky, and you must take steps to eradicate identifying information, including specific IP addresses

Sanitizing and Obfuscation

Even header information should be “sanitized” IP addresses may show specific personal behavior

and should be changed, but in a way that doesn't negate the analysis of traffic Internet2 observatory deletes the rightmost 11 bits of all

addresses in stored flow data Several tools exist; if you write a program consider

precedents carefully, there are pitfalls In stored packet data, the “content” can be

erased, which should not matter unless checksums are being studied

The “My ex is a net admin” - FAQ Can my net admins read my email by sniffing?

Probably not, if you always choose the “secure” encrypted protocols, such as IMAPS, POPS, or web mail that uses SSL. ITS email set-up instructions will always specify secure protocols.

Can my ex tap my Internet phone conversations? Skype – no. It is AES encrypted, unless you call

China, Dubai, Pakistan, India (???) Some others, perhaps. But ex would need access

to the right links, and ex would be subject to criminal prosecution

The “I am a net admin” FAQ How should I protect myself?

Tirelessly explain your monitoring activities to co-workers and supervisors and invite them to participate

Don't see anything you shouldn't Capture as little as possible, take pains to protect

(set permissions, encrypt) any stored capture data and get rid of it as soon as possible

Remember everything Yoda said about the nature of the Dark Side

Network Intrusion Detection Systems

A sniffer allows you to look at packets, a NIDS looks at them for you

Free ones: Snort

Probably the broadest community support, medium difficulty to get going, they're trying to capitalize the signatures now, to support Snort

AIDE Bro

Invented by Vern Paxson (an Orwellian reminder that monitoring comes hand in

hand with the potential for privacy violations)

Snorting (snort.org)

Snort compares packets using “rules”, which are defined one-by-one to detect specific things, although some are heuristic

To get to know Snort, you should disable all but one or two rules and see how that goes, and then add more rules to suit your needs

Bro (bro-ids.org )

How is Bro different from Snort?

Snort is solely signature based, meaning that it looks for very specific content in the network stream and reports each instance of a particular signature. Bro can analyze network traffic at a much higher-level of abstraction, and has powerful facilities for storing information about past activity and incorporating it into analyses of new activity. Bro also provides a signature mechanism similar to Snort's.

(excerpted from http://bro-ids.org/FAQ.html )

Intrusion Prevention System (IPS)

SniffsExamines trafficTakes action

Interesting to note – although the Wikipedia article for NIDS lists examples, the IPS article does not.

Darknets and Honeypots

A darknet (compare honeynet) is an empty network with a sniffer on it. The idea is that scanning attempts and “backscatter” from various activities will appear on the net as security references

Contrast with honeypot, which is a decoy machine set up to detect intrusion attempts, etc.

ICMP Backscattertcpdump -ln -i eth1 -w noping-icmp.cap 'icmp[icmptype] !=

icmp-echo and icmp[icmptype] != icmp-echoreply'Captured with tcpdump, displayed in Wireshark.

Traffic Characterization/Identification

Task of seeing what kind of traffic is on net Harder than it looks TCP/UDP port numbers are often meaningless Many apps are port-agile BitTorrent uses HTTP-style protocol, sometimes

on port 80 Effective traffic identification involves seeing

every header and understanding protocols Also interesting to sort by geographic location

(per MaxMind GeoIP )

Byte-Value Distribution Histograms

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MP4 Stream

Stdev % of a-mean

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SSL

Byte-Value Distribution Histograms Stdev

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IPSec ESP

Text emphasizes a small set of characters, Binary streams (audio/video) involve more widely spread valuesEncryption aspires to appear random, and therefore has a flat distribution

Stuff with a text-like distribution is probably text, even if obscuredStuff with an exceptionally flat distribution is probably encryptedUDP-based stuff with double digit % std dev may be audio/video

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WAV Audio

SNMP

Although more secure(-ish) flavors have been developed, the vast majority of SNMP is SNMP versions 1 or 2c.

Access control is generally through a “community” name which is generally well known and visible on the wire in SNMP packets

Using community “public” is negligent insanity If your network printer is using the factory

config, it's a sitting duck

Netflow

Routers and switches send information about network “flows” to a flow collector.

Flows include source and destination addresses, port (TCP or UDP) numbers, router interface, and volume of traffic

Flows usually reflect less than 100% of traffic through a router.

Free tools for dealing with netflow data are available (e.g. flow-tools); not as cool as sniffer tools

Routers, switches provide extensive information about what they're doing

Interface packet/byte counts, up-time, temperatures, route tables, forwarding caches, etc.

Servers, printers, wireless APs, SOHO gateways SNMP provides variables for a mgmt station to query,

or traps, which are messages initiated by the router, switch, printer, etc, in question.

Simple Network Management Protocol(SNMP)

Topology Discovery

In a network where you know the SNMP community names, it is reasonably simple to use bridge and route tables to discover network topology. This provides a list of network devices (routers, switches), and interfaces.

Non-Passive Monitoring

NMAP Scans for listening TCP/UDP services on a host

Other scanners apply tests for vulnerabilities SAINT MetaSploit Nessus (source moved from open to closed) OpenVAS (fork of Nessus's open source)

Network quality checking: web100

The Web100 add-ons for Linux allow an observer to collect stats on TCP connections, to determine whether the network is performing well Info available includes indicators of congestion,

TCP host tuning, and throughput Examples apps that use web100: NDT, NPAD

Host accounting

It is necessary to account for the computers on a network for many reasons Host infections Unacceptable behaviors Identifying stolen devices

This can be done by gathering ARP/ND tables using SNMP, or by parsing switch logs or DHCP server logs.

Host OS Survey (Perl fragment)if ($pkt =~ /(User-Agent: .*)/i) {$matchcounter++; my $ua = $1; $ua =~ s/^user-agent: //i; print "$ipsrcadd^$ua\n"; } “User-Agent: is placed in an HTTP request

header by a browser, and most identify the operating system in use, but not a specific host. This example never captures anything but UA.

Service accounting

ngrep -d eth1 -O ngrep-server-hdrs2.cap -q "HTTP/.*Server: .*Content-Type: text/" \(src net 128.171 or src net 132.160 or src net 166.122 or src net 168.105\) Find HTTP servers on our nets, regardless of port

tcpdump -i eth0 -ln 'tcp[13] & 18 = 18' and src port 25 Find services answering TCP port 25 (commonly

SMTP)