Malicious Code and Intruders

Dr. Ron Rymon

Efi Arazi School of Computer Science

IDC, Herzliya, 2010/11

Pre-requisite: Basic Cryptography, Authentication

Overview

Malicious Code (Viruses) Intrusion Detection and Prevention Denial of Service

Malicious Code (Viruses)

Main Sources: Stallings, F-Secure

Types of Malicious Code

Need Host Program

Independent

Trapdoors Logic Bombs

TrojanHorses

Viruses Bacteria Worms

Malicious Code

Replicate

Bowles and Pelaez

Spyware

Most current malicious code mixes all capabilities

Historical Perspective Original computer virus idea – Fred Cohen, MIT 1984

– A few primitive virus-like programs existing beforehand First viruses

– Spread slowly, appending to boot sector, programs (Jerusalem 87) Faster infection

– Worms– E-mails, mobile code in browsers

New targets– Mobile viruses – IKEE.B– Devices – Stuxnet

“Commercialization”– Spy and espionage– Harvest information– Cyber terror

Trap Doors and Logic Bombs Trap Door:

– Secret part of a program that circumvents normal security procedures– E.g., Undocumented server planted by the developer, Debug code within

legitimate application

Logic bomb– A program that is set to explode when certain conditions occur– Examples: when the programmer is fired, on the expiration date of the

license

Easter Eggs– Hidden code that is inserted by the software programmers for fun or to

show that they control the software (look at eeggs.com)– Usually not destructive (not really a bomb)

Solutions:– Independent QA and code review, Real-time detection (firewall)

Spyware (and Adware) Adware

– Started as advertising banners within free software– Can usually remove advertising if you pay software license

Spyware– Usually, some free software will also collect information about you– Primarily surfing habits, cookies, etc. but who knows what else…– Also, sometimes you are essentially running a server on your machine

which can serve for further penetration Spyware-like activity by legitimate software vendors

– Designed to facilitate auto-update and version synchronization– Some record various characteristics of the client machine

Corporate spies– Corporate spies may install software that records email, browsing, etc.

• E.g., Israeli Trojan at major corporations

Solutions:– Use anti-spyware software (independent or part of OS)– Exit-control and information leakage software– Personal firewall can usually catch outgoing messages

Trojan Horses Legitimate user inadvertently lets it in behind perimeter

Malware hidden within another software – usually installed by a privileged user– when invoked may perform the unwanted function

Malware impersonating another software– Replacing/hiding existing OS programs (rootkits)

Malware sent by email that prompts the user to install it Malware installed when the user visits a web site

– Russian mafia broke into legitimate web servers and planted trojans

Examples: keystroke logger, DDoS zombies, NetBus, rootkits Solutions: anti-virus, host-based IDSs, hardened OS, security

policies, personal firewall

Example: Triggering Email

NetBus Trojan

Viruses, Worms, and Bacteria Programs that replicate themselves over the network

– Often try to hide themselves from detection

Viruses: add own code to a host program– Replicates through exchange of programs between systems– May mutate to spread more quickly and avoid detection

Worms: independent program that replicates over network• Morris Worm crashed many Unix networks• Klez is an email worm• Code Red exploited IIS holes, mutated• Kelvir spreads in IM networks• SQL Slammer attacks MS-SQL servers• IKEE.B spreads between iphones over wi-fi

Bacteria: a program that replicates itself– Choke CPU, disk space, etc.– Email bombs are also a type of bacteria

Speed of Infection

(source: F-secure white paper)

Anti-Virus Approaches Detection modes

– Scan incoming information (emails, communication ports, …)– Scan disk and memory for infected files

Detection methodologies– Search for previously identified “signatures”

• takes time for signatures to be discovered and distributed• viruses may compress themselves and the host program• polymorphic viruses change their signature

– More sophisticated pattern recognition• identify parts of virus code and more general patterns• identify virus by its actions rather than its structure• emulate the execution of the virus until it decompresses itself

– identify signature of uncompressed virus– identify virus behavior

• 75-90% of new (unknown) viruses can be discovered

– Maintain cryptographic checksums of important files, to prevent alteration (Tripwire)

Anti-Virus Approaches Newer detection methods

– Sandbox approach• execute the virus in separate partition• entrap the virus to infect and turn itself in

– Digital Immune System (IBM – now Symantec)• Centralized identification of new viruses• Automated distribution of detection and fix to others on network

– Market trends: move from Desktop to Server to Both Removal of the threat

– remove the virus from the infected program– quarantine infected programs and content

Prevention– Avoid disks, downloads, from unrecognized / uncertified sources– Use an anti-virus program to scan all new content

Hoaxes– Some hoaxes disguise a virus as a solution

Study of Off-the-shelf Anti Virus Software (2006)

Tested by AV-Test against 59000 backdoors, 70,000 bots, and 160000 Trojans– Five vendors scored over 99%– Four tested below 50%– Median only 90.42%

One conclusion: use multi-layers– Outgoing mail– Server side– ISP scanners– And finally client…

Intrusion Detection and Prevention

Main Sources: Network Intrusion Detection / Northcutt, Novak

The Honeynet Project

Intruders – Who and Why Who

– Internal users (70% !!)– Opponents (corporate, political)– Vandals– Kids (mentally)– Criminals!

Why– Stealing your money

• Credit cards, passwords to bank accounts, extortion and blackmail– Other profit:

• trade secrets, classified information, free usage of service– Vandalism

• erase / modify information, interruption of service– Show off– Take control of a machine as a stepping stone to attacking another

Intrusion - How Insecure system configuration

– default configurations, password cracking, trust between systems, trust between application and database (access control)

– Unpatched machines (about half of all PCs) – zero-day attack

Software bugs– buffer overflows, unexpected input combinations, race conditions

Flaws in security protocols or their use– sniffing on wireless communication

Social engineering– Take advantage of human weaknesses

Trojan methods– getting a program running on a privileged user machine

A Typical Intrusion Scenario1. Intelligence 1: collect publicly available information

• about organization, network, people, email accounts

2. Intelligence 2: scan the network to:• which IP addresses are in use• what TCP or UDP ports are “open”• what operating system / services are in use• unpatched systems

3. Run “exploit” scripts against vulnerable nodes

4. Get access to Shell program (ideally as a superuser)

5. Run more exploits• install backdoor for future use• try not to leave any tell-tales behind

6. Remotely access the system / backdoor

Examples of Reconnaissance

Ping sweeps– identify which machines are alive

TCP and UDP scans– identify open ports

ICMP queries– OS identification, including patch versions

Account scans– break into weak user accounts (passwords!)

Example: LANGuard Scanning Tool

Examples of Exploits Hackers try to identify any type of service or program that

can be exploited

CGI Scripts– pass tainted input to shell, ask for a file

Web server attacks (and SQL server, and other servers)– execute malformed or misplaced file names– buffer overflow

Web client (browser)– execute mobile code– hiding 1x1pixel frames within a trusted web page

SMTP, and IMAP attacks– bugs in sendmail (SMTP) and in IMAP servers

IP Spoofing– DoS attacks, masquerading

DNS Attacks– poisoning through masquerading and abuse of answer caching

Intruder Tools: ICMP Scanning ICMP can be used to identify live hosts and open ports

Scan 1: send range of echo requests– Randomly– To a subnet broadcast IP: usually 255, 0 in BSD

Scan 2: send range of address mask requests– routers will respond with info on the network addressing space

Scan 3: use traceroute to collect “host unreachable” and “port unreachable” responses

Solutions:– disable traffic to broadcast IPs (also helps in DoS attacks)– disable ICMP echo – But, will not have ping, traceroute capabilities

Intruder Tools: DNS Attacks (1) If compromised, DNS can provide a full map of the domain without

additional effort Hackers must first identify the identity of the DNS server, and if

possible the version of the BIND (Berkeley Internet Domain Daemon) software it runs– use nslookup to identify name of domain name server– use dig (Domain Internet Groper) to identify BIND version

Older BIND versions may divulge some host information– using a simple query– sometimes allows not just a single query, but a list of all domain records– these records may include host information such as OS, CPU– masquerade as secondary DNS and perform full “zone transfer” to

download all DNS information Or, may try to traceroute using the DNS port 53, if ICMP ports are

blocked, looking for “host unreachable” replies

Intruder Tools: DNS Attacks (2) DNS cache poisoning

– A query from a compromised host that includes tainted input in the response field can result in DNS poisoning

• this was used in the Clinton-Giuliani senate race to divert traffic from hillary2000.com to hillaryno.com

Solutions– Upgrade BIND version

• BIND 8.3 and up includes DNS Security Extensions (DNSSEC), requiring stronger authentication of querying servers

– Limit zone transfers to few known servers

– Do not fill DNS records with extra information

Intruder Tools: Identify OS, Server Intruders wish to identify the software on the other side, so they can

select proper exploits Stimuli-based OS scanning tools (e.g., nmap)

– telnet, ftp, will sometimes “banner” the OS– unsolicited FIN to open port: some TCP stacks will respond– bogus or no TCP flag values: some OS will keep the flags in reply– extra TCP data

Passive fingerprinting– Examine TCP packets, looking for a specific OS standard practice– Traceroute, with TTL=n-1, to see where coming from– Important when investigating an attack in real-time

Crashing attempts– Using DoS methods

Most of the techniques rely on improper implementations of certain protocols (or incomplete specification)

Intruder Tools: Masquerading Typical scenario

– Identify and characterize trust relationship between two systems– Attack one system, e.g. using DoS, or by crashing it– Impersonate the silenced system to perform the crime– Cover the crime scene

Example: the Mitnick Attack– Identified trusted TCP relationship between X-terminal and Server– Silenced the Server using SYN flooding DoS attack– Hijacked TCP connection to x-terminal, by spoofing as Server IP– Changed trusted domain to “all”, so that can access later– Logged out, and stopped Server flooding, to avoid detection

Solutions– Identify and “drop” SYN floods– Avoid trust relationships– Deploy tools that detect changes to critical files (e.g. tripwire)

Intruder Tools: Buffer Overflow A favorite of intruders, taking advantage of ill-

implemented protocols and software– Most recent attacks use buffer overflow, e.g., slammer

Scenario:– transfer more data than the receiving party has reserved space for– embed your code, in the hope that it will be placed in the receiver

program code space, and subsequently executed (use nops to avoid exact calculation)

A double-whammy for “kiddy” intruders: intrusion success + demonstrated superiority over other programmers

Solutions:– Vendor patches– More importantly: educate programmers and run code reviews– New CPUs allow marking data areas as non-executable

Intrusion Detection Goals:

– prevent damage– prevent illegitimate use of resources, access to information, etc.– catch and deter intruders– identify weaknesses to improve defenses

Important to detect before intruder gains access– most detection efforts concentrate on intelligence gathering scans– Common assumption: Intruders behave differently

Unfortunately, easier to identify after the fact (forensic)

Methods:– rule-based detection, using known patterns (signatures)– statistical anomaly analysis– most systems use combination of both– System integrity verifiers (Tripwire), honey pots

NIDS and HIDS Network-based IDSs (NIDS) consist of agents that monitor

network traffic Host-based IDSs (HIDS) consist of agents that monitor a single

system

Most deployments consist of– multiple instances of

NIDS and HIDS

– a centralized Console, as part of Security Operations Center (SOC)

Use baselining to reduce false positives

Signature/Rule-based Detection Hundreds of intrusion signatures have been identified

– Maintained by CERT and the like

Features used in signatures (and statistical detection)– Packets cooked in a specific way– Which resources/services are requested– Whether the request is successful– Frequency, order, and length of usage– Concurrent processes of same user and of other users– Time of the day– Who is the user– Physical machine from which a request is made

Statistical Anomaly Analysis Use profiles for individual users Choose threshold to distinguish

Note: not much data to build profile of intruder

Honeypots and Honey Nets A honeypot is a decoy system that is placed within the

internal network and is designed to attract intruders– Usually configured as a characteristic system in same network– May contain decoy and made-up data– A little weaker than other systems– IDS installed, and carefully monitored

Goals:– Deception– Detection and advance warning (usually the actual attack is

preceded by intelligence gathering)

Another variation is an externally placed “scout” with bogus information– May identify itself to the outside as any of the network servers– Will continue the exchange with the hacker, and will alert

IDS Challenges Encryption makes it difficult to identify patterns / attack Number of attempts

– Honey nets have shown that unadvertised networks are attacked within a few hours

– Most attempts are “standard” (downloaded) exploits, tried blindly Large number of false positives

– In a production environment, legitimate users may exhibit a behavior that matches a signature

– Many organizations routinely ignore IDS warnings– Some attempts to model legitimate usage, and exclude rest

False negatives– Many new intrusion techniques are invented continuously

Overhead– IDS adds an overhead to a system– Administrator may choose not to install on a critical system

Vulnerability Assessment Idea: use hacker-like tools to test systems

– Point to known weaknesses– Recommend fixes

Security Administrator’s Tool for Analyzing Networks (SATAN)– One of the first research tools– Was later used by hackers

Vulnerability assessment tools use– Various scanning techniques– Code for hundreds of intrusions, DoS schemes– Pointers to fixes

Organizations use routinely penetration testing (“pentest”)– Network and application levels

Common vulnerability Scoring System (CVSS) standardizes vulnerability risks

Social Engineering Conning people into giving up their security

– Usually, masquerading as an authorized user– Sometimes, presenting to simple users as administrator– Examples

• IRC chats• calling up helpdesk• emails and web messages offering help

Breach IT and sometimes physical security– Installing Trojans, DDoS zombies– Stealing information– Destroying data

Famous BBB – Bribery, Bending, Burglary

Most IT security efforts focus on technology – more shall be spent on training people

Audit Trails Organizations collect and maintain activity logs

Main driver: regulatory requirements

Main goals:– Identify usage patterns and alert to anomalies– Forensic investigation

Platforms and applications regularly log activity

Log management systems– Centralized repository– Correlate for users across systems/apps– Correlate usage patterns and reports on exceptions

Prevention Policies and Tools Stronger and well specified protocols Stronger implementation of protocols Strong authentication Access control policies Audit and prosecution Firewalls Proxies Vulnerability Assessment Tools More…

Conclusion: No single solution to security

Very important: education and awareness of staff

Denial of Service

Main Sources: CMU CERT, Riverhead, Northcutt et al

Denial Of Service (DOS) Interruption: prevent legitimate users access to a service Typical motives: political hacktivism, show off, blackmail

Denial Of Service (DOS) Typical methods

– Flooding of a network– Prevent connection between two or more machines– Prevent connection between one machine (server or

client) and other machines– Crash a system, or network configuration

Examples:– Echo, SYN attacks on web servers, and ISPs– Worms aimed at crashing email servers– Attacks on specific application services– DNS attacks that also divert traffic

DOS: SYN Attack Works at TCP layer

– Normal TCP 3-way handshake: SYN, followed by SYN/ACK, followed by ACK

– After SYN/ACK, server maintains an open connection until ACK is received

Attack: flood server with IP spoofed SYNs until server exceeds the number of open connections allowed– Server will not be able to service legitimate users and may crash

Detection: too many open SYN requests Prevention:

– To protect others, do not allow outgoing packets to have a source that is not from your network (i.e. is spoofed)

– Can also be done by the ISP

DOS: Echo-CharGen Attack Works in UDP layer

– Echo returns a packet to sender– Chargen generates and returns a character

Attack: connect a CharGen service to an Echo service– Results in a self sustained flood of communications– Sometimes the spoofed address is a broadcast address, resulting in

more bandwidth

Prevention:– eliminate unnecessary UDP services– If must provide such services, use firewall to set up acceptable

policy

DOS: Smurf Attack A variation on the Echo attack

Attack: send an echo to a subnet’s broadcast address (subnet.255), from a spoofed IP (victim)– As a result, all machines on the subnet respond simultaneously to

the victim machine, flooding it

Prevention:– block packets addressed to broadcast from outside the network

– Note that the victim can do little, since even if his router blocks the packets, they will still jam the network between the router and the ISP

DOS: E-Mail Spamming Attack Use email servers to clog themselves and other email

servers– Code Red, Love Letter

Attack: Send a large email to a large number of recipients– Directly to lists

– Email worms

Prevention:– Identify source and block its packets

– Prevent large emails, large distribution lists

Other DOS Attacks Crashing a server by using a faulted implementation of a

communication protocol– Teardrop uses improperly implemented TCP fragment reassembly– Land sends SYN packets with same source and destination

addresses– Ping of Death sends oversized (>65K) ICMP command

Intentionally generating errors that are logged by the server to clog log files and consume disk space

Placing large files on ftp areas or network shared storage

Generating excessive logins until system blocks logins from legitimate users– Many OS will block an account after 3-5 failed login attempts

Distributed DOS (DDOS) Attack: Orchestrated from multiple sources at same time

Solution: Identify packets addressed to attacked server, divert other traffic, and filter “dirty” packets

Examples of DDOS

ICMP/UDP floods: TFN, Trinoo

Code Red is a worm that has flood period from 20th to 27th of each month

Social engineering is often used to get people to download DDOS daemons (zombies)

In some cases, the attacker collaborate, e.g., coordinated Arab attacks on Israeli sites

Example 1: DDoS for Hire

Example 2: DDoS Extortion Extortion letter sent to domain administrators (Aug 2010)

Not clear whether senders are really capable or a simple scam

Zombies on innocent computers

DDoS Illustration

Server-level DDoS attacks

Infrastructure-level DDoS attacks

Bandwidth-level DDoS attacks

Source: Riverhead

Riverhead Guard

Victim

Non-victimized servers

Traffic destined to the victim

Legitimate traffic to victim

“No Dynamic configuration”

5. Forward the legitimate

Solution Overview

4. Filter only the bad

6. Non Victimtraffic free flows

Source: Riverhead

Adaptive and Dynamic Filtering

Static &Dynamic

Filters

Anti spoofing Statistical analysis

Rate-limiting& DDoS Traffic Shaping

Layer 7httpsmtp

1 to 1000s of dynamic filters by

flow, protocol,

…

Per flow queues

and aggregate rates

Block spoof packets:TCP, DNS, UDP

Anomaly recognition,Per flow, using a base line.

Filter: Drop non-essential traffic.E.g., ICMP, UDP if not essential, etc.

Source: Riverhead

ISP Perimeter Protection

Source: Riverhead

ISP Perimeter Protection

Source: Riverhead

Tempest Attacks

Tempest Attacks Transient ElectroMagnetic Pulse Emanation Standard; or

Telecommunications Electronic Material Protected from Emanating Spurious Transmissions

A US Army project in the 1950s, designed to protect against electromagnetic eavesdropping

Idea: eavesdrop on electromagnetic radiation (from monitors,disk drives), to decode the activity/content

Wim Van Eck (1985), shows that this is possible from a distance of up to 1Km.

Anderson & Kuhn (1998) present a method for processing the electromagnetic waves, and also a way to defend against it using Tempest-proof fonts.

Tempest Attacks

http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf

Today’s monitors emit less radiation, making it harder

US embassies are routinely shielded to prevent Tempest espionage– There are also NATO standard and a commercial one

There probably are easier methods for industrial espionage