Binary Exploitation: Buffer Overflows and Defense

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Questions and Answers

What is the primary goal of subverting execution in malware?

To display error messages

To consume system resources

To crash the program

To execute the attacker's code (correct)

What type of attack occurs when an attacker manipulates a buffer to execute arbitrary code?

Buffer Overflow (correct)

Heap Overflow

SQL Injection

Format String Attack

What is the purpose of the frame pointer (EBP) in a program?

To store the previous frame pointer (correct)

To store the stack pointer

To store the return address

To store local variables

What is the purpose of the stack pointer (ESP) in a program?

To point to the top of the stack Signup and view all the answers

What occurs when a program writes data beyond the buffer boundaries?

Buffer Overflow Signup and view all the answers

What is the purpose of the return address on the stack?

To store the address to return to Signup and view all the answers

What happens to the program when it runs with canaries?

The program gets aborted due to stack smashing Signup and view all the answers

What is the purpose of the gs segment in the context of canaries?

To pick out canaries from thread local data Signup and view all the answers

What is the purpose of the ADC instruction?

To add with carry Signup and view all the answers

What is the purpose of the ND/NX bit in Intel/AMD processors?

To mark non-code regions as non-executable Signup and view all the answers

What is the main advantage of the lazy binding scheme?

It delays binding until the invocation of the function Signup and view all the answers

What is the limitation of Non-Executable Stacks (W^X) in preventing buffer overflow attacks?

It does not work for programs that need to execute from the stack Signup and view all the answers

What is DEP an abbreviation for?

Data Execution Prevention Signup and view all the answers

What is the role of the GOT entry in the lazy binding scheme?

It simply jumps back to the PLT entry Signup and view all the answers

What is the purpose of the PLT entry?

To invoke an offset in the procedure linkage table Signup and view all the answers

What happens during the first invocation of a function in the lazy binding scheme?

The PLT entry jumps to the GOT entry, which jumps back to the PLT entry Signup and view all the answers

What is the relationship between the PLT and the GOT in the lazy binding scheme?

The PLT and GOT are separate tables with indirect references Signup and view all the answers

What is a gadget in the context of building a payload?

A short sequence of instructions followed by a return instruction Signup and view all the answers

What is the purpose of Step 1 in building a payload?

To find gadgets in the libc library Signup and view all the answers

What does the ret instruction do in a 32-bit machine?

Pops the contents pointed to by ESP into EIP and increments ESP by 4 Signup and view all the answers

What is the purpose of stitching gadgets together?

To build the payload Signup and view all the answers

What is necessary to build a payload if a suitable function in libc does not exist?

Build a custom function Signup and view all the answers

What is the purpose of Step 3 in building a payload?

To construct the stack Signup and view all the answers

What is the purpose of the GOT?

To store the actual address of a function Signup and view all the answers

What happens when the resolver is invoked?

The resolver resolves the actual address of a function and fills it into the GOT Signup and view all the answers

What is an advantage of using a PLT?

Functions are relocatable and resolved only on need Signup and view all the answers

What is a way to bypass ASLR?

Brute force Return-to-PLT Signup and view all the answers

What is a safer programming language mentioned in the text?

Rust Signup and view all the answers

What is an example of a securer library function?

gets_s Signup and view all the answers

Study Notes

Binary Exploitation Overview

Two main components of malware: subverting normal execution behavior and payload execution.
Various attack vectors for subverting execution include SQL injection at the application level and buffer overflows, double frees, and format string issues at the system level.

Buffer Overflows

Stack management is vital for understanding buffer overflows in software.
Stack structure consists of parameters, return addresses, and local variables during function execution.
Local variables are organized in memory from high addresses to low addresses within the stack.

Stack Usage

Stack layout includes function parameters, return address, frame pointers, and local variables.
Global Offset Table (GOT) and Procedure Linkage Table (PLT) are essential for method resolution and function calls.

Address Space Layout Randomization (ASLR)

ASLR makes functions relocatable, improving security by complicating memory access patterns.
Techniques for bypassing ASLR include brute force methods, return-to-PLT, and timing attacks.

Mitigation Techniques

Safer programming languages like Java and C# enforce memory safety but aren't viable replacements for C/C++.
Techniques like utilizing secure libraries (e.g., C11 annex K functions) enhance protection against buffer overflows.

Canary Mechanism

Canaries are special guard values placed on the stack used to detect buffer overflow attempts.
The presence of canaries can abort program execution if the canary value is altered.

Non-Executable Stacks (W^X)

Intel/AMD processors feature a non-executable bit (ND/NX) marking code regions as non-executable to prevent executing attacker-controlled data.
Data Execution Prevention (DEP) is implemented in major operating systems, though it can interfere with specific applications such as JIT compilers.

Function Call Mechanics

Lazy binding delays function resolution until it’s needed, reducing load times.
PLT acts as an interface that helps bind function calls to their respective addresses dynamically.

Return-Oriented Programming (ROP)

In cases where specific functions do not exist, attackers can create an execution flow using "gadgets"—short sequences of instructions ending with a return.
Building a ROP payload involves finding gadgets within libc and stitching them together to create the desired execution sequence.

Finding Gadgets

Gadget extraction involves static analysis to identify sequences ending with return instructions.
Gadgets can be either intentional compiler-generated or unintended and useful for crafting ROP chains.

Key Execution Concepts

Stack exploitation can lead to control over execution flow, making buffer overflow attacks significantly dangerous.
Importance of understanding the stack structure, call mechanics, and mitigation strategies is crucial in securing applications against exploitation.

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Description

Learn about buffer overflows, return-to-libc, ROP, canaries, W^X, and ASLR in binary exploitation. Understand how attackers subvert execution and use payloads to compromise systems. Explore defense mechanisms against buffer overflows and other attacks.