SCSC 555 Computer Security

Chapter 10 Malicious softwarePart B

Index

Social Engineering Malware Payload Countermeasures of malware DDoS Buffer overflow

Social Engineering

Tricking user to assist in the comprise of their own systems or personal information Spam e-mail

Most spam is sent by botnets using compromised user systems

Advertising, scams, carrier of malware (attachment), or phishing attack

Trojan horse program A useful, or apparently useful program or utility

containing hidden code that performs some unwanted or harmful funciton

Social Engineering

Trojan horse program E.g. claim to be antivirus scanner, security update

actual carrying payload such as spyware Three models of Trojan horses

Continuing to perform the function of the original program and additionally performing a separate malicious activity

… but modifying the function to perform malicious activity

Performing a malicious function that completely replaces the function of the original program

Malware Payload

System corruption Data destruction Ransomware, e.g. Gpcode Trojan Real-world damage: cause damage to physical

equipment Logic bomb: is set to “explode” when certain

conditions are met

Malware Payload

Attack agent Bot: malware subverts the computational and

network resources of infected system for use by the attacker

The uses of bots: DDoS attack, Spamming … Botnet: the collection of bots often is capable of

acting in a coordinated manner.

Malware Payload Information theft

Keyloggers and Spyware What is a keylogger? (next slide)

Countermeasure to keylogger Spyware

Phishing and Identity theft URL of fake Web site controlled by the attacker Spear-phishing: an email claiming to be from a trusted

sources, the recipients are carefully researched by the attacker greatly increases the likehood of the recipient responding as desired by the attacker

Malware Payload

Backdoor and Rootkit Backdoor (trapdoor) is a secret entry point into a

program without going through the usual security access procedures

Rootkit is a set of programs installed on a system to maintain covert access to that system with root privileges, while hiding evidence of its presence Make many changes to a system to hide its existence Difficult to detect

Keyloggers Keyloggers are used to capture

keystrokes on a computer Hardware Software

Software Behaves like Trojan programs

Hardware Easy to install Goes between the keyboard and the

CPU KeyKatcher and KeyGhost

Countermeasures of malware

Ensure all systems are current All patches applied

Set appropriate access controls on the applications and data to reduce the number of files that any user can

access Training the users to against social

engineering attack

Countermeasures of malware

Technical mechanism to mitigate threat Detection Identification Removal

Requirements for effective malware countermeasures Generality, Timeliness, Resiliency, minimal DOS costs,

transparency, global and local coverage

Countermeasures of malware

Four generations of antivirus software 1st generation 2nd generation 3rd generation 4th generation

More sophisticated antivirus approaches Host-based behavior-blocking Perimeter scanning approaches

(Reading page 323 – 327)

Distributed Denial-of-Service (DDoS) Attacks

DDoS attack on a host from multiple servers or workstations

Network could be flooded with billions of requests Loss of bandwidth Degradation or loss of speed

Often participants (zombies) are not aware they are part of the attack Thousands zombies are controlled by the attacker via

Trojan programs

DDoS Tools and Countermeasures

DDoS countermeasures: • Security patches from software vendors• Antivirus software• Firewalls: Ingress (inbound) and egress (outbound) filtering

(details next …)

Buffer Overflow Attacks A vulnerability in poorly written code

does not check predefined size of input field

Goal of buffer overflow attack: Fill overflow buffer with executable code OS executes this code, elevates attacker’s permission

Administrator Owner of running application

To stop software exploits Train your programmer in developing applications with security in

mind Stay appraised of latest security patches provided by software

vendors

Buffer Overflow Exploits

Buffer Overflow Exploits is the Most common cause of Internet attacks

Over 50% of advisories published by CERT (computer security incident report team) are caused by various buffer overflows

Morris worm (1988): overflow in fingerdInfected 10% of the existing Internet

CodeRed (2001): overflow in MS-IIS server300,000 machines infected in 14 hours

SQL Slammer (2003): overflow in MS-SQL server75,000 machines infected in 10 minutes

Buffer is a data storage area inside computer memory (stack or heap) Intended to hold pre-defined amount of data

If more data is stuffed into it, it spills into adjacent memory

If executable code is supplied as “data”, victim’s machine may be fooled into executing it Code will self-propagate or give attacker control over

machine

Attack can exploit any memory operation Pointer assignment, format strings, memory allocation

and de-allocation, function pointers, calls to library routines via offset tables

Memory Buffers

Stack Buffers

Suppose Web server contains this functionvoid func(char *str) {

char buf[126]; strcpy(buf,str); }

When this function is invoked, a new frame with local variables is pushed onto the stack

Allocate local buffer(126 bytes reserved on stack)

Copy argument into local buffer

Top ofstack

Stack grows this way

buf sfpret

addr str

Local variables Pointer toprevious

frame

Frame of thecalling function

Execute code at

this address after func()

finishes

Arguments

What If Buffer is Overstuffed? Memory pointed to by str is copied onto stack…

void func(char *str) { char buf[126]; strcpy(buf,str); }

If a string longer than 126 bytes is copied into buffer, it will overwrite adjacent stack locations

strcpy does NOT check whether the string at *str contains fewer than 126 characters

Top ofstack

buf strFrame of thecalling function

This will beinterpreted

as return address!

overflow

Executing Attack Code

Suppose buffer contains attacker supplied string For example, *str contains a string received from the network as

input to some network service daemon

When function exits, code in the buffer will be executed, giving attacker a shell

The attacker gets a root shell if the victim program is SUID root

Top ofstack

code strFrame of thecalling function ret

Attacker puts actualinstructions into his input string, e.g.,

binary code of execve(“/bin/sh”)

In the overflow, a pointer backinto the buffer appears in

the location where the systemexpects to find return address

Executable attack code is stored on stack, inside the buffer containing attacker’s string Stack memory is supposed to contain only data, but…

Overflow portion of the buffer must contain correct address of attack code in the RET position The value in the RET position must point to the beginning

of attack code in the buffer Otherwise application will crash with segmentation

violation Attacker must know or correctly guess in which stack

position his buffer will be when the function is called

Some Issues on Buffer Overflow

The Cause : No Range Checking strcpy does not check input size

strcpy(buf, str) simply copies memory contents into buf starting from *str until “\0” is encountered

Ignoring the size of area allocated to buf

Many C library functions are unsafe strcpy(char *dest, const char *src) strcat(char *dest, const char *src) gets(char *s) scanf(const char *format, …) printf(const char *format, …)

Examples of Common Buffer Overflow Attacks

Examples of Common Buffer Overflow Attacks