CWE-676: Use of Potentially Dangerous Function

What is Use of Potentially Dangerous Function?

• Overview: Use of potentially dangerous functions refers to the invocation of functions that, if used incorrectly, can introduce security vulnerabilities. These functions can be safe when used with caution and proper validation.

• Exploitation Methods:

• Attackers exploit this vulnerability by manipulating inputs to dangerous functions to cause buffer overflows, format string vulnerabilities, or arbitrary code execution.
• Common attack patterns include injecting malicious input or exploiting assumptions made in the code about input size and structure.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access, data corruption, and execution of arbitrary code.
• Potential cascading effects include system crashes, data breaches, and escalation of privileges.
• Business impact can involve loss of customer trust, legal liabilities, and financial damage due to exploits.

• Prevention Guidelines:

• Specific code-level fixes include validating inputs, using safer alternatives to dangerous functions, and applying bounds checking.
• Security best practices involve regularly reviewing code for unsafe function usage and adopting secure coding standards.
• Recommended tools and frameworks include static analysis tools to detect unsafe function calls and memory management libraries like Safe C/C++ Libraries that provide safer alternatives.

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Technical Details

Likelihood of Exploit: High

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

C Example

// This code uses the `gets()` function, which is dangerous because it does not check the bounds of the buffer.
// This can lead to buffer overflow vulnerabilities if the input size exceeds the buffer capacity.

#include <stdio.h>

void vulnerableFunction() {
    char buffer[50];
    printf("Enter your input: ");
    gets(buffer); // Vulnerable line: `gets()` does not limit the input size
    printf("You entered: %s\n", buffer);
}

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

Explanation

In this vulnerable example, the gets() function is used to read input into a buffer. The problem with gets() is that it does not perform bounds checking, meaning it will continue to read input until a newline is encountered, regardless of the buffer's capacity. If the input exceeds the buffer size, it can overwrite adjacent memory, leading to a buffer overflow vulnerability. This can be exploited by an attacker to execute arbitrary code or cause a program crash.

How to fix Use of Potentially Dangerous Function?

Fixed Code Example

// This code replaces the dangerous `gets()` function with `fgets()`, which respects buffer size limits.
// This prevents buffer overflow by ensuring that input cannot overflow the buffer's boundaries.

#include <stdio.h>

void secureFunction() {
    char buffer[50];
    printf("Enter your input: ");
    if (fgets(buffer, sizeof(buffer), stdin) != NULL) { // Secure line: `fgets()` limits input to the buffer size
        printf("You entered: %s\n", buffer);
    } else {
        printf("Error reading input.\n");
    }
}

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

Explanation

In the fixed example, fgets() is used instead of gets(). The fgets() function reads up to sizeof(buffer) - 1 characters from stdin, ensuring that the buffer is not overflowed and leaving space for the null terminator. This prevents buffer overflow vulnerabilities. Additionally, the return value of fgets() is checked to ensure that input was successfully read, which is a good practice for robust error handling. This change is crucial for maintaining the integrity and security of the program when dealing with user input.