Chapter 4: Malware

Worm Propagation

Worms propagate by finding and infecting vulnerable hosts. -They need a way to tell if a host is vulnerable -They need a way to tell if a host is already infected

Insider Attacks

a security breach that is caused or facilitated by someone who is a part of the very organization that controls or builds the asset that should be protected. In the case of malware, an insider attack refers to a security hole that is created in a software system by one of its programmers.

Rootkit Revealer

-By Bryce Cogswell and Mark Russinovich (Sysinternals) -Two scans of file system -High-level scan using the Windows API -Raw scan using disk access methods -Discrepancy reveals presence of rootkit -Could be defeated by rootkit that intercepts and modifies results of raw scan operations

Early History

1972 sci-fi novel "When HARLIE Was One" features a program called VIRUS that reproduces itself First academic use of term virus by PhD student Fred Cohen in 1984, who credits advisor Len Adleman with coining it In 1982, high-school student Rich Skrenta wrote first virus released in the wild: Elk Cloner, a boot sector virus (c)Brain, by Basit and Amjood Farooq Alvi in 1986, credited with being the first virus to infect PCs

Trojan Horse

A Trojan horse (or Trojan) is a malware program that appears to perform some useful task, but which also does something with negative consequences (e.g., launches a keylogger). Trojan horses can be installed as part of the payload of other malware but are often installed by a user or administrator, either deliberately or accidentally. Visible Action: Something Useful Invisible Action: Something malicious

Backdoors

A backdoor, which is also sometimes called a trapdoor, is a hidden feature or command in a program that allows a user to perform actions he or she would not normally be allowed to do. When used in a normal way, this program performs completely as expected and advertised. But if the hidden feature is activated, the program does something unexpected, often in violation of security policies, such as performing a privilege escalation. Benign example: Easter Eggs in DVDs and software

Computer Viruses

A computer virus, or simply virus, is computer code that can replicate itself by modifying other files or programs to insert code that is capable of further replication. This self-replication property is what distinguishes computer viruses from other kinds of malware, such as logic bombs. Another distinguishing property of a virus is that replication requires some type of user assistance, such as clicking on an email attachment or sharing a USB drive.

Computer Worms

A computer worm is a malware program that spreads copies of itself without the need to inject itself in other programs, and usually without human interaction. Thus, computer worms are technically not computer viruses (since they don't infect other programs), but some people nevertheless confuse the terms, since both spread by self-replication. In most cases, a computer worm will carry a malicious payload, such as deleting files or installing a backdoor.

Adware

A form of privacy-invasive software that displays advertisements on a user's screen against their consent. Typically, an adware program is installed on a user's computer because he visits an infected web page, opens an infected email attachment, installs a shareware or freeware program that has the adware embedded in a Trojan horse, or as the result of being victimized by a computer virus or worm. Once it is installed and running in the background, an adware program will periodically pop up an advertisement on the user's screen.

Logic Bombs

A logic bomb is a program that performs a malicious action as a result of a certain logic condition. The classic example of a logic bomb is a programmer coding up the software for the payroll system who puts in code that makes the program crash should it ever process two consecutive payrolls without paying him. Another classic example combines a logic bomb with a backdoor, where a programmer puts in a logic bomb that will crash the program on a certain date.

Biological Analogy

Computer viruses share a number of properties with biological viruses. Attack-Penetration-Replication and Assembly-Release

Rootkits

A rootkit modifies the operating system to hide its existence -E.g., modifies file system exploration utilities -Hard to detect using software that relies on the OS itself

Quarantine

A suspicious file can be isolated in a folder called quarantine: --E.g,.if the result of the heuristic analysis is positive and you are waiting for db signatures update The suspicious file is not deleted but made harmless: the user can decide when to remove it or eventually restore for a false positive --Interacting with a file in quarantine it is possible only through the antivirus program The file in quarantine is harmless because it is encrypted Usually the quarantine technique is proprietary and the details are kept secret

The Omega Engineering Logic Bomb

An example of a logic bomb that was actually triggered and caused damage is one that programmer Tim Lloyd was convicted of using on his former employer, Omega Engineering Corporation. On July 31, 1996, a logic bomb was triggered on the server for Omega Engineering's manufacturing operations, which ultimately cost the company millions of dollars in damages and led to it laying off many of its employees.

Defenses against Insider Attacks

Avoid single points of failure. Use code walk-throughs. Use archiving and reporting tools. Limit authority and permissions. Physically secure critical systems. Monitor employee behavior. Control software installations.

Propagation: Practice

Cumulative total of unique IP addresses infected by the first outbreak of Code-RedI v2 on July 19-20, 2001

Dynamic Analysis

Check the execution of codes inside a virtual sandbox Monitor --File changes --Registry changes --Processes and threads --Networks ports

Static Analysis

Checks the code without trying to execute it Quick scan in white list Filtering: scan with different antivirus and check if they return same result with different name Weeding: remove the correct part of files as junk to better identify the virus Code analysis: check binary code to understand if it is an executable, e.g., PE Disassembling: check if the byte code shows something unusual

Propagation Theory

Classic epidemic model -N: total number of vulnerable hosts -I(t): number of infected hosts at time t -S(t): number of susceptible hosts at time t -I(t)+S(t)=N -b: infection rate Differential equation for I(t): -dI/dt = bI(t) S(t) More accurate models adjust propagation rate over time

Signature Database

Common Malware Enumeration (CME) --aims to provide unique, common identifiers to new virus threats --Hosted by MITRE --http://cme.mitre.org/d ata/list.html Digital Immune System (DIS) --Create automatically new signatures

Resources

Computer Emergency Response Team --Research center funded by the US federal government --Vulnerabilities database Symantec --Reports on malware trends --Database of malware Art of Computer Virus Research and Defense by Peter Szor

Encrypted virus

Decryption engine + encrypted body Randomly generate encryption key Detection looks for decryption engine

Other Undecidable Detection Problems

Detection of a virus --by its appearance --by its behavior Detection of an evolution of a known virus Detection of a triggering mechanism --by its appearance --by its behavior Detection of a virus detector - by its appearance --by its behavior Detection of an evolution of --a known virus --a known triggering mechanism --a virus detector

Metamorphic Virus

Different virus bodies Approaches include code permutation and instruction replacement Challenging to detect

Virus Phases

Dormant Propagation Triggering Action

Propagation Phase

During this phase, the virus is replicating itself, infecting new files on new systems.

Dormant Phase

During this phase, the virus just exists—the virus is laying low and avoiding detection.

Concealment

Encrypted virus Polymorphic virus Metamorphic Virus

Polymorphic virus

Encrypted virus with random variations of the decryption engine (e.g.,padding code) Detection using CPU emulator

Early Worms History

First worms built in the labs of John Shock and Jon Hepps at Xerox PARC in the early 80s CHRISTMA EXEC written in REXX, released in December 1987, and targeting IBM VM/CMS systems was the first worm to use e-mail service The first internet worm was the Morris Worm, written by Cornell student Robert Tappan Morris and released on November 2, 1988

Online Anti Virus Software

Free browser plug-in Authentication through third party certificate (i.e. VeriSign) No shielding Software and signatures update at each scan Poorly configurable Scan needs internet connection Report collected by the company that offers the service

Professional Malware

Growth in professional cybercrime and online fraud has led to demand for professionally developed malware New malware is often a custom- designed variations of known exploits, so the malware designer can sell different "products" to his/her customers. Like every product, professional malware is subject to the laws of supply and demand. --Recent studies put the price of a software keystroke logger at $23 and a botnet use at $225.

Worm development

Identify vulnerability still un-patched Write code for -Exploit of vulnerability -Generation of target list ---Random hosts on the internet ---Hosts on LAN ---Divide-and-conquer -Installation and execution of payload -Querying/reporting if a host is infected Initial deployment on botnet Worm template -Generate target list -For each host on target list ---Check if infected ---Check if vulnerable ---Infect ---Recur Disturbed graph search algorithm -Forward edges: infection -Back edges: already infected or not vulnerable

Triggering Phase

In this phase, some logical condition causes the virus to move from a dormant or propagation phase to perform its intended action.

Action Phase

In this phase, the virus performs the malicious action that it was designed to perform, called payload. This action could in- clude something seemingly innocent, like displaying a silly picture on a computer's screen, or something quite malicious, such as deleting all essential files on the hard drive.

Shield vs. On-Demand

Shield: --Background process (service/daemon) --Scans each time a file is touched (open, copy, execute, etc.) On-demand: --Scan on explicit user request or according to regular schedule --Onasuspiciousfile, directory, drive, etc. BOTH: Performance test of scan techniques --Comparative: check the number of already known viruses that are found and the time to perform the scan --Retrospective: test the proactive detection of the scanner for unknown viruses, to verify which vendor uses better heuristics Anti-viruses are ranked using both parameters: http://www.av-comparatives.org/

White/Black Listing

Maintain database of cryptographic hashes for --Operating system files --Popular applications --Known infected files Compute hash of each file Look up into database Needs to protect the integrity of the database

Viruses, Worms, Trojans, Rootkits

Malware can be classified into several categories, depending on propagation and concealment Propagation - Virus:human-assisted propagation (e.g.,open email attachment) -Worm : automatic propagation without human assistance Concealment - Rootkit: modifies operating system to hide its existence - Trojan: provides desirable functionality but hides malicious operation Various types of payloads, ranging from annoyance to crime

Malware Zombies

Malware can turn a computer into a zombie, which is a machine that is controlled externally to perform malicious attacks, usually as a part of a botnet. Attacker commands botnets to attack the victim computer.

Financial Impact

Malware often affects a large user population Significant financial impact, though estimates vary widely, up to $100B per year (mi2g) Examples -LoveBug (2000) caused $8.75B in damages and shut down the British parliament -In 2004, 8% of emails infected by W32/MyDoom.A at its peak -In February 2006, the Russian Stock Exchange was taken down by a virus.

Economics of Malware

New malware threats have grown from 20K to 1.7M in the period 2002- 2008 Most of the growth has been from 2006 to 2008 Number of new threats per year appears to be growing an exponential rate.

Infection Types

Overwriting -Destroys original code Pre-pending -keeps original code, possibly compressed Infection of libraries -Allows virus to be memory resident -E.g. kernel32.dil Macro Viruses -Infects MS Office documents -Often installs in main document template

Offline Anti Virus Software

Paid annual subscription Installed on the OS Software distributed securely by the vendor online or a retailer System shielding Scheduled software and signatures updates Easily configurable Scan without internet connection Report collected locally and may be sent to vendor

Signatures

Scan compare the analyzed object with a database of signatures A signature is a virus fingerprint --E.g.,a string with a sequence of instructions specific for each virus --Different from a digital signature A file is infected if there is a signature inside its code --Fast pattern matching techniques to search for signatures All the signatures together create the malware database that usually is proprietary

Spyware

Spyware is privacy-invasive software that is installed on a user's computer without his consent and which gathers information about a user, his computer, or his computer usage without his consent. A spyware infection will typically involve the use of one or more programs that are always running in the background, collecting information. Periodically, these programs will contact a data collection agent and upload information it has gathered from the user.

The Omega Bomb Code

The Logic Behind the Omega Engineering Time Bomb included the following strings: 7/30/96 -Event that triggered the bomb. F: -which focused attention to volume F, which had critical files F:\LOGIN\LOGIN 12345 - Login a fictitious user, 12345 (the back door) CD \PUBLIC: Moves to the public folder of programs FIX.EXE /Y F:\*.* - Run a program, called FIX, which actually deletes everything PURGE F:\/ALL - Prevent recovery of the deleted files

Virus Detection is Undecidable

Theoretical result by Fred Cohen (1987) Virus abstractly modeled as program that eventually executes infect Code for infect may be generated at runtime Proof by contradiction similar to that of the halting problem Suppose program isVirus(P) determines whether program P is a virus Define new program Q as follows: if (not isVirus(Q)) infect stop Running isVirus on Q achieves a contradiction

Current Trends

Trojans currently have largest infection potential -Often exploit browser vulnerabilities -Typically used to download other malware in multi-stage attacks

Heuristic Analysis

Useful to identify new and "zero day" malware Codeanalysis --Based on the instructions, the antivirus can determine whether or not the program is malicious, i.e., program contains instruction to delete system files, Execution emulation --Run code in isolated emulation environment --Monitor actions that target file takes --If the actions are harmful, mark as virus Heuristic methods can trigger false alarms

Degrees of Complication

Viruses have various degrees of complication in how they can insert themselves in computer code. a) A simple injection at the beginning of a program. (b) A more complex injection that splits the virus code into two parts and injects them at different points in the program. Jump instructions are used to begin execution with the virus code and then pass control to the original program code.