Software Security

Introduction

Software Security involves writing code that is resistant to attacks. It differs from secure computing (using security tools) by focusing on making the software itself secure.

Software Vulnerabilities

Common Vulnerability Types

• Unvalidated Input: Not checking user input before processing
• Buffer Overflow: Writing beyond array boundaries
• Integer Overflow: Arithmetic operations exceeding limits
• Format String: Using user input in format functions
• Race Conditions: Timing issues in concurrent code
• SQL Injection: Injecting SQL through user input
• XSS: Injecting scripts into web pages

Buffer Overflow

A buffer overflow occurs when data exceeds a buffer's boundaries and overwrites adjacent memory.

How It Works

1. Program allocates fixed-size buffer
2. Input exceeds buffer size
3. Data overflows into adjacent memory
4. Attacker can overwrite return addresses
5. Execution can be redirected to malicious code

// Vulnerable code
void vulnerable_function(char *str) {
    char buffer[50];
    strcpy(buffer, str);  // No bounds checking!
}

// Attack: Pass string longer than 50 chars
// Overwrites return address, hijacking execution

Types of Buffer Overflow

• Stack-based: Overflow on the stack
• Heap-based: Overflow on the heap
• Format String: Using printf-style functions improperly

Defenses

• Stack Canaries: Detect overwrites before return
• ASLR: Randomize memory addresses
• DEP/NX: Mark memory as non-executable
• Safe Functions: Use strncpy instead of strcpy

Malware Types

Secure Programming Practices

Input Validation

• Validate all user input
• Use allowlists (not blocklists)
• Check type, length, format, range
• Reject invalid, don't try to fix

Memory Safety

• Use safe string functions (strncpy, snprintf)
• Check array bounds
• Avoid manual memory management where possible
• Use modern languages (Rust, Go)

Least Privilege

• Run with minimum necessary privileges
• Drop privileges when not needed
• Use sandboxing