CWE-788: Access of Memory Location After End of Buffer

What is Access of Memory Location After End of Buffer?

• Overview: Access of Memory Location After End of Buffer occurs when a program accesses memory beyond the allocated buffer, often due to incorrect index or pointer arithmetic. This is common in languages like C and C++ where manual memory management is prevalent.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting input that manipulates the buffer index, causing the program to read or write to unauthorized memory.
• Common attack patterns include buffer overflows and heap manipulations, where malicious code is injected or executed.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized data access, corruption of memory, or application crashes.
• Potential cascading effects include security breaches, data leakage, or system instability.
• Business impact may involve compromised sensitive information, loss of customer trust, and financial losses due to downtime or legal repercussions.

• Prevention Guidelines:

• Specific code-level fixes include bounds checking before accessing buffer elements and using safe functions that automatically handle buffer sizes.
• Security best practices involve rigorous input validation, avoiding unsafe functions like gets(), and employing modern language features or libraries that handle memory safely.
• Recommended tools and frameworks include static analysis tools to detect buffer overflows and runtime protections like AddressSanitizer to catch out-of-bounds access during testing.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

C Example

#include <stdio.h>

void readArrayElements(int *arr, int size) {
    // Off-by-one error in loop condition
    for (int i = 0; i <= size; i++) {  
        // Potential out-of-bounds access
        printf("Element %d: %d\n", i, arr[i]);  
    }
}

int main() {
    int numbers[5] = {1, 2, 3, 4, 5};
    // Passes size of array as parameter
    readArrayElements(numbers, 5);  
    return 0;
}

Explanation

• The code demonstrates a classic off-by-one error in the loop condition (i <= size). This causes the loop to access memory beyond the allocated array, leading to undefined behavior or potential security vulnerabilities. The loop should only iterate over valid indices from 0 to size - 1.

How to fix Access of Memory Location After End of Buffer?

To fix this vulnerability, ensure that the loop iterates only within the valid indices of the array. The correct loop condition should be i < size, which ensures the loop does not attempt to access memory outside the bounds of the array. Additionally, consider using safer constructs or functions that handle boundary checks automatically to prevent similar issues.

Fixed Code Example

#include <stdio.h>

void readArrayElements(int *arr, int size) {
    // Corrected loop condition to prevent out-of-bounds access
    for (int i = 0; i < size; i++) {  
        printf("Element %d: %d\n", i, arr[i]);
    }
}

int main() {
    int numbers[5] = {1, 2, 3, 4, 5};
    readArrayElements(numbers, 5);
    return 0;
}

Explanation

• The loop condition is corrected to i < size, which ensures that the loop iterates only over valid index positions of the array. This simple adjustment prevents the potential out-of-bounds access issue.
• Always validate array indices and consider using functions or constructs that inherently manage bounds checking, such as using higher-level languages or safer libraries, to reduce the risk of buffer overflows and similar vulnerabilities.
• This example adheres to best practices for C by ensuring proper bounds checking and preventing undefined behavior due to accessing memory outside of the allocated array.