CWE-785: Use of Path Manipulation Function without Maximum-sized Buffer

What is Use of Path Manipulation Function without Maximum-sized Buffer?

• Overview: This vulnerability arises when a software product uses a function to modify or normalize paths or filenames without ensuring the output buffer is large enough to handle the maximum possible input size, leading to potential buffer overflows.

• Exploitation Methods:

• Attackers can exploit this by supplying a long path or filename input that exceeds the expected buffer size.
• Common techniques include crafting input strings that deliberately overflow the buffer to overwrite adjacent memory.

• Security Impact:

• Direct consequences include buffer overflow, which can lead to arbitrary code execution or crashes.
• Potential cascading effects include unauthorized access to system resources or data corruption.
• Business impact might involve data breaches, system downtime, and loss of customer trust.

• Prevention Guidelines:

• Ensure that output buffers are sized according to the maximum possible input size, using constants like PATH_MAX.
• Implement input validation to verify the length of paths and filenames before processing.
• Use safe functions that automatically handle buffer sizes or provide error handling for overflow conditions.
• Regularly update and patch software to address known vulnerabilities.
• Consider using static analysis tools to detect potential buffer overflow issues in the codebase.

Corgea can automatically detect and fix Use of Path Manipulation Function without Maximum-sized Buffer in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Windows provides a large number of utility functions that manipulate buffers containing filenames. In most cases, the result is returned in a buffer that is passed in as input. (Usually the filename is modified in place.) Most functions require the buffer to be at least MAX_PATH bytes in length, but you should check the documentation for each function individually. If the buffer is not large enough to store the result of the manipulation, a buffer overflow can occur.

Vulnerable Code Example

// Vulnerable code demonstrating CWE-785
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>  // For PATH_MAX

void normalize_path(const char *input_path) {
    char buffer[256];  // Insufficient buffer size; may not accommodate long paths
    // Using realpath() without ensuring buffer is large enough for PATH_MAX
    if (realpath(input_path, buffer) == NULL) {  // Potential buffer overflow
        perror("Error resolving path");
        exit(EXIT_FAILURE);
    }
    printf("Normalized Path: %s\n", buffer);
}

int main() {
    const char *path = "/some/very/long/path/that/exceeds/256/characters/...";
    normalize_path(path);
    return 0;
}

Explanation of the Vulnerability

In this vulnerable code example, the buffer used in the normalize_path function is set to a fixed size of 256 bytes. This is insufficient for handling potentially longer paths, which could exceed this size, leading to a buffer overflow. The realpath() function is used without ensuring that the buffer is large enough to accommodate the maximum possible path length defined by PATH_MAX. This oversight can lead to undefined behavior, including memory corruption and security vulnerabilities.

How to fix Use of Path Manipulation Function without Maximum-sized Buffer?

Fixed Code Example

// Fixed code addressing CWE-785
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>  // For PATH_MAX

void normalize_path(const char *input_path) {
    char buffer[PATH_MAX];  // Use PATH_MAX to ensure buffer is large enough
    // Safely using realpath() with buffer of size PATH_MAX
    if (realpath(input_path, buffer) == NULL) {
        perror("Error resolving path");  // Proper error handling
        exit(EXIT_FAILURE);              // Exit if realpath() fails
    }
    printf("Normalized Path: %s\n", buffer);
}

int main() {
    const char *path = "/some/very/long/path/that/exceeds/256/characters/...";
    normalize_path(path);
    return 0;
}

Explanation of the Fix

In the fixed code example, the buffer size is defined using PATH_MAX, which ensures that it can accommodate any path that the system might generate or process. This change eliminates the risk of buffer overflow by guaranteeing that the buffer is sufficiently large for the longest possible path. Additionally, the code checks if realpath() returns successfully and handles any errors appropriately by printing an error message and exiting the program. This approach follows best practices in C programming, making the code safer and more robust.