Presentation buffer overflow attacks and theircountermeasures

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Buffer overflow attacks take advantage of vulnerabilities in C and C++ programs that do not perform bounds checking on buffers. An attacker can exploit this by writing past the end of a buffer to corrupt memory and hijack the program flow. Common countermeasures include writing secure code with bounds checking, enabling stack protection features of compilers, and using runtime protections like Address Space Layout Randomization. However, none can prevent all possible attacks.

Buffer Overflow Attacks and Their
Countermeasures

118232K – NDY Tharindu

Buffer Overflow: the Basics
● Buffer overflow problems always have been associated with
security vulnerabilities.
● A buffer is a contiguous allocated chunk of memory, such as
an array or a pointer in C.
● In C and C++, there are no automatic bounds checking on
the buffer, which means a user can write past a buffer.

int main () {
int buffer[10];
buffer[20] = 10;
}

Problem with the program
● The above C program is a valid program, and
every compiler can compile it without any
errors.
● However, the program attempts to write
beyond the allocated memory for the buffer.
● Programs written in C/C++ languages, where
more focus is given to the programming
efficiency and code length than to the security
aspect.

Memory layout of a Process
primarily the program code, i.e., a series of executable
program instructions.

initialized and uninitialized
global data

allocated at run time

The heap holds dynamic variables. To
allocate memory, the heap uses the malloc
function or the new operator.

The stack is used to store function call-by
arguments, local variables and values of selected
registers

Example
void function (int a, int b, int c) {
char buffer1[5];
char buffer2[10]
FP is need to access a, b, c, buffer1 and buffer2 variables.
}
●

● All these variables are cleaned up from the stack as the
int main() { function terminates

function(1,2,3);
}

10 bytes
5 bytes
frame
pointer

Example 2
void function (char *str) {
char buffer[16];
strcpy (buffer, str);
}
int main () {
char *str = "This is greater than 16 bytes"; // length of str = 27 bytes
function (str);
}
● Guaranteed to cause unexpected behavior.
● String (str) of 27 bytes has been copied to a location (buffer) that has been allocated for only 16 bytes.
● The extra bytes run past the buffer and overwrites the space allocated for the FP & return addresses.
● This, in turn, corrupts the process stack.

This is a example how buffer overflow can overwrite a function's return address,
● which in turn can alter the program's execution path.
● Recall that a function's return address is the address of the next instruction in memory, which is executed
immediately after the function returns. Hacker might get a root shell by adding execution path to such code.
● Or place the code we are trying to execute in the buffer's overflowing area

Buffer Overflow Countermeasures
● The solutions proposed for buffer overflow problems mainly
target the prevention of large-scale system attacks through
the loopholes described above.

● None of the methods described above can claim to prevent
all possible attacks.

● Write secure code:
C library functions such as strcpy (), strcat (), sprintf () and
vsprintf () operate on null terminated strings and perform no
bounds checking.

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The document discusses buffer overflows, which occur when user input exceeds the maximum size of a buffer and overwrites other areas of memory. This can allow malicious users to execute arbitrary code by injecting machine code into the overflowed buffer. The document provides examples of stack layout, shellcode payloads, and prevention techniques like bounds checking functions and security mechanisms like ASLR.

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This document discusses various techniques for auditing source code to discover vulnerabilities, including both automated and manual methods. It describes tools like Cscope, Ctags, and source code analysis tools. It also covers common classes of vulnerabilities that may be found through source code auditing, such as format string vulnerabilities, off-by-one errors, integer conversion issues, uninitialized variable usage, and race conditions in multithreaded code. Effective methodologies discussed include searching for specific vulnerable code patterns, understanding application logic from entry points, and focusing on attacker-controlled input handling.

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Introduction to Stack Buffer Over‌flow for beginnersKhashayar Fereidani

This presentation introduces stack buffer overflows and exploitation techniques for beginners. It discusses how buffer overflows work, potential impacts of exploitation including gaining system access and installing backdoors. It then demonstrates a sample vulnerable code, its disassembly, and how an attacker could exploit it by overwriting the return address on the stack to redirect execution to shellcode that starts a calculator program. The presentation concludes by reviewing protections like ASLR and DEP and a real-world exploit.

C - aptitude3Srikanth

The document contains summaries of code snippets and explanations of technical concepts. It discusses: 1) How a code snippet with post-increment operator i++ would output a garbage value. 2) Why a code snippet multiplying two ints and storing in a long int variable would not give the desired output. 3) Why a code snippet attempting to concatenate a character to a string would not work. 4) How to determine the maximum number of elements an array can hold based on its data type and memory model. 5) How to read data from specific memory locations using the peekb() function in C.

C aptitude questionsSrikanth

CNIT 127: Ch 2: Stack overflows on LinuxSam Bowne

The document discusses stack overflows in Linux, particularly focusing on buffer overflows and their exploits. It covers the structure of the stack, the processes involved when functions are called, and examples of how vulnerabilities can be exploited using tools like GDB. The text emphasizes the lack of bounds-checking in C and C++, highlighting potential security risks associated with improper memory access.

Low Level Exploitshughpearse

This document discusses various low-level exploits, beginning with creating shellcode by extracting opcodes from a compiled C program. It then covers stack-based buffer overflows, including return-to-stack exploits and return-to-libc. Next it discusses heap overflows using the unlink technique, integer overflows, and format string vulnerabilities. The document provides code examples and explanations of the techniques.

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127 Ch 2: Stack overflows on LinuxSam Bowne

Bt0067 c programming and data structures2Techglyphs

Ch 18: Source Code AuditingSam Bowne

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Introduction to Stack Buffer Over‌flow for beginnersKhashayar Fereidani

C - aptitude3Srikanth

C aptitude questionsSrikanth

CNIT 127: Ch 2: Stack overflows on LinuxSam Bowne

Low Level Exploitshughpearse

Presentation buffer overflow attacks and theircountermeasures

1. Buffer Overflow Attacks and Their Countermeasures 118232K – NDY Tharindu

2. Buffer Overflow: the Basics ● Buffer overflow problems always have been associated with security vulnerabilities. ● A buffer is a contiguous allocated chunk of memory, such as an array or a pointer in C. ● In C and C++, there are no automatic bounds checking on the buffer, which means a user can write past a buffer. int main () { int buffer[10]; buffer[20] = 10; }

3. Problem with the program ● The above C program is a valid program, and every compiler can compile it without any errors. ● However, the program attempts to write beyond the allocated memory for the buffer. ● Programs written in C/C++ languages, where more focus is given to the programming efficiency and code length than to the security aspect.

4. Memory layout of a Process primarily the program code, i.e., a series of executable program instructions. initialized and uninitialized global data allocated at run time The heap holds dynamic variables. To allocate memory, the heap uses the malloc function or the new operator. The stack is used to store function call-by arguments, local variables and values of selected registers

5. Example void function (int a, int b, int c) { char buffer1[5]; char buffer2[10] FP is need to access a, b, c, buffer1 and buffer2 variables. } ● ● All these variables are cleaned up from the stack as the int main() { function terminates function(1,2,3); } 10 bytes 5 bytes frame pointer

6. Example 2 void function (char *str) { char buffer[16]; strcpy (buffer, str); } int main () { char *str = "This is greater than 16 bytes"; // length of str = 27 bytes function (str); } ● Guaranteed to cause unexpected behavior. ● String (str) of 27 bytes has been copied to a location (buffer) that has been allocated for only 16 bytes. ● The extra bytes run past the buffer and overwrites the space allocated for the FP & return addresses. ● This, in turn, corrupts the process stack. This is a example how buffer overflow can overwrite a function's return address, ● which in turn can alter the program's execution path. ● Recall that a function's return address is the address of the next instruction in memory, which is executed immediately after the function returns. Hacker might get a root shell by adding execution path to such code. ● Or place the code we are trying to execute in the buffer's overflowing area

7. Buffer Overflow Countermeasures ● The solutions proposed for buffer overflow problems mainly target the prevention of large-scale system attacks through the loopholes described above. ● None of the methods described above can claim to prevent all possible attacks. ● Write secure code: C library functions such as strcpy (), strcat (), sprintf () and vsprintf () operate on null terminated strings and perform no bounds checking.

Presentation buffer overflow attacks and theircountermeasures

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