CWE-474: Use of Function with Inconsistent Implementations

What is Use of Function with Inconsistent Implementations?

• Overview: This vulnerability arises when code uses a function that behaves differently across various operating systems or versions. Such inconsistencies can lead to unexpected behavior, especially when software is used in an environment different from the one it was developed or tested in. This can create security risks if the function behaves in an insecure manner on some platforms.

• Exploitation Methods:

• Attackers can exploit this by triggering different behaviors on platforms where the function implementation is insecure.
• Common attack patterns include passing parameters that are interpreted differently or leveraging platform-specific security flaws within the function.

• Security Impact:

• Direct consequences include unexpected program behavior, crashes, or security breaches if sensitive operations are mishandled.
• Potential cascading effects involve data corruption, unauthorized access, or denial-of-service conditions.
• Business impact could be significant, including loss of customer trust, legal ramifications, and financial losses due to breaches.

• Prevention Guidelines:

• Specific code-level fixes include avoiding the use of functions known for inconsistent implementations and using platform-independent libraries or APIs.
• Security best practices involve thoroughly testing code across all target platforms and environments to ensure consistent behavior.
• Recommended tools and frameworks include static analysis tools to detect potentially unsafe function use and adopting cross-platform libraries that abstract away platform differences.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, PHP, Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

// Vulnerable code demonstrating the use of the 'gets' function, which has inconsistent implementations across different platforms
#include <stdio.h>

int main() {
    char buffer[256];
    printf("Enter a string: ");
    gets(buffer); // Inconsistent implementation: 'gets' is unsafe and behavior can vary across platforms.
    printf("You entered: %s\n", buffer);
    return 0;
}

Explanation:

The code above uses the gets function to read input from the user. The gets function is unsafe because it does not perform bounds checking, which can lead to buffer overflow vulnerabilities. Additionally, its behavior is inconsistent across different platforms, which can result in unpredictable behavior. This function has been removed from the C11 standard due to these issues.

How to fix Use of Function with Inconsistent Implementations?

To address the issues with gets, we should replace it with a safer alternative like fgets, which allows specifying the maximum number of characters to read, thereby preventing buffer overflows and ensuring consistent behavior across different platforms.

Best Practices for Fixing the Issue:

• Replace gets with fgets, specifying the size of the buffer to prevent overflow.
• Always check the return value of fgets to ensure successful input reading.
• Prefer using functions that are part of the latest standards (e.g., C11 or later) to ensure better portability and security.

Fixed Code Example

// Fixed code using 'fgets' instead of 'gets' to ensure consistent and safe input handling
#include <stdio.h>

int main() {
    char buffer[256];
    printf("Enter a string: ");
    if (fgets(buffer, sizeof(buffer), stdin) != NULL) { // Use 'fgets' to limit input size and ensure consistent behavior
        printf("You entered: %s", buffer); // 'fgets' retains newline character, if present
    } else {
        printf("Error reading input.\n");
    }
    return 0;
}

Explanation:

In the fixed code, we replaced gets with fgets. The fgets function reads input safely by limiting the number of characters read to the size of the buffer, thus preventing buffer overflows. It also ensures consistent behavior across different platforms. The return value of fgets is checked to handle any potential input errors gracefully. Additionally, fgets retains the newline character if present, so there's no need to add a newline character explicitly when printing the output.