CWE-460: Improper Cleanup on Thrown Exception

What is Improper Cleanup on Thrown Exception?

• Overview: This vulnerability occurs when a program fails to properly clean up resources or maintain a consistent state after an exception is thrown, leading to unexpected behavior or execution paths.

• Exploitation Methods:

• Attackers can exploit this by forcing exceptions in critical parts of the program to cause resource leaks or inconsistent states.
• Common attack patterns include triggering exceptions at strategic points to bypass security checks or disrupt normal program logic.

• Security Impact:

• Direct consequences of successful exploitation include resource leaks, data corruption, or application crashes.
• Potential cascading effects might involve unauthorized access, data breaches, or denial-of-service conditions.
• Business impact can include financial losses, damage to reputation, and legal liabilities due to compromised data integrity or availability.

• Prevention Guidelines:

• Specific code-level fixes include using finally blocks or equivalent constructs to ensure cleanup occurs regardless of exceptions.
• Security best practices involve thorough exception handling strategies and ensuring all paths through the code result in proper resource management.
• Recommended tools and frameworks include static analysis tools to identify potential cleanup issues and language-specific libraries that manage resources safely.

Corgea can automatically detect and fix Improper Cleanup on Thrown Exception in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Medium

Affected Languages: C, C++, Java, C#

Affected Technologies: Not specified

Vulnerable Code Example

// Vulnerable code demonstrating improper cleanup on exception

#include <stdio.h>
#include <stdlib.h>

void process_data() {
    FILE *file = fopen("data.txt", "r");
    if (!file) {
        // File could not be opened
        perror("Failed to open file");
        return;
    }

    int *buffer = (int*)malloc(100 * sizeof(int));
    if (!buffer) {
        // Memory allocation failed
        // File is not closed before returning, leading to a resource leak
        perror("Failed to allocate memory");
        return;
    }

    // Simulate an exception-triggering condition
    if (fgetc(file) == EOF) {
        // Improper cleanup; buffer is not freed, and file is not closed
        perror("Error reading from file");
        return;
    }

    // Normal processing
    // ...

    // Proper cleanup in normal execution flow
    free(buffer);
    fclose(file);
}

int main() {
    process_data();
    return 0;
}

How to fix Improper Cleanup on Thrown Exception?

To fix this vulnerability, ensure that all allocated resources are properly released, even when exceptions or errors occur. In C, this involves manually freeing memory and closing files. Use a goto statement to jump to cleanup sections that are consistently executed before any return, reducing code duplication and ensuring that resources are always freed.

Fixed Code Example

// Fixed code with proper cleanup using goto for error handling

#include <stdio.h>
#include <stdlib.h>

void process_data() {
    FILE *file = fopen("data.txt", "r");
    if (!file) {
        perror("Failed to open file");
        return;
    }

    int *buffer = (int*)malloc(100 * sizeof(int));
    if (!buffer) {
        perror("Failed to allocate memory");
        goto cleanup_file; // Ensures the file is closed if allocation fails
    }

    // Simulate an exception-triggering condition
    if (fgetc(file) == EOF) {
        perror("Error reading from file");
        goto cleanup; // Ensures both buffer is freed and file is closed
    }

    // Normal processing
    // ...

cleanup:
    free(buffer); // Ensures buffer is freed in all paths
cleanup_file:
    fclose(file); // Ensures file is closed in all paths
}

int main() {
    process_data();
    return 0;
}

In the fixed code, the use of goto for error handling ensures that both the file and memory are always cleaned up, regardless of where an error occurs. This approach is crucial in C, where automatic resource management is not available as it is in higher-level languages. By organizing the cleanup code in labeled sections, we maintain readability and ensure resources are consistently released, preventing resource leaks.