CWE-126: Buffer Over-read

What is Buffer Over-read?

• Overview: Buffer Over-read occurs when a program reads data beyond the boundary of a buffer, potentially accessing adjacent memory locations. This typically results from improper use of indexes or pointers when accessing buffers.

• Exploitation Methods:

• Attackers can exploit buffer over-reads to access sensitive information stored in adjacent memory.
• Common attack patterns include crafting inputs that cause the program to read beyond the intended buffer size.

• Security Impact:

• Direct consequences include information leakage, where an attacker can gain unauthorized access to sensitive data.
• Potential cascading effects involve system crashes or erratic application behavior due to corrupted memory access.
• Business impact can be severe, including data breaches, loss of customer trust, and legal liabilities due to unauthorized exposure of sensitive information.

• Prevention Guidelines:

• Specific code-level fixes include validating buffer sizes and ensuring all buffer accesses remain within their boundaries.
• Security best practices involve rigorous input validation, using safer functions that limit reads to the buffer size, and employing static or dynamic analysis tools to detect buffer over-reads.
• Recommended tools and frameworks include using compilers and static analysis tools that offer buffer boundary checking, such as GCC with address sanitizers, and adopting safe libraries or language features that handle buffer management automatically.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

C Example for CWE-126: Buffer Over-read

#include <stdio.h>
#include <string.h>

void print_user_input(const char* input) {
    char buffer[8];  // Small buffer size
    // Copy user input into buffer without checking its length
    strcpy(buffer, input); // Vulnerable to buffer over-read
    // Print the content of the buffer
    printf("User input: %s\n", buffer);
}

int main() {
    // User input that is larger than the buffer size
    char user_input[] = "This input is too long for the buffer!";
    print_user_input(user_input);
    return 0;
}

Explanation:

• The vulnerability here is that strcpy() is used to copy user input into a fixed-size buffer without checking the input length. If the input exceeds the buffer size, it can lead to a buffer overflow, potentially causing undefined behavior or security issues such as data corruption or crash.

How to fix Buffer Over-read?

Fixed Code Example

#include <stdio.h>
#include <string.h>

void print_user_input(const char* input) {
    char buffer[8];  // Small buffer size
    // Safely copy user input into buffer with length check
    strncpy(buffer, input, sizeof(buffer) - 1); // Copy at most 7 characters
    buffer[sizeof(buffer) - 1] = '\0'; // Ensure null termination
    // Print the content of the buffer
    printf("User input: %s\n", buffer);
}

int main() {
    // User input that is larger than the buffer size
    char user_input[] = "This input is too long for the buffer!";
    print_user_input(user_input);
    return 0;
}

Explanation:

• Line 7-8: strncpy() is used instead of strcpy(). It copies at most sizeof(buffer) - 1 characters to ensure there is space for the null terminator.
• Line 9: Explicitly sets the last character of the buffer to '\0' to ensure proper null-termination.
• This approach prevents buffer over-read by ensuring that the buffer never holds more data than it can safely manage, thus mitigating potential security vulnerabilities. This method also follows best practices by ensuring that the buffer is always null-terminated.