CWE-690: Unchecked Return Value to NULL Pointer Dereference
Learn about CWE-690 (Unchecked Return Value to NULL Pointer Dereference), its security impact, exploitation methods, and prevention guidelines.
What is Unchecked Return Value to NULL Pointer Dereference?
• Overview: Unchecked Return Value to NULL Pointer Dereference is a vulnerability where software fails to verify if a function call returns a NULL pointer, potentially leading to a program attempting to access or modify memory at that pointer location, which can cause crashes or unexpected behavior.
• Exploitation Methods:
- Attackers may exploit this vulnerability by triggering error conditions that result in a function returning a NULL pointer, leading the application to dereference it without checks.
- Common attack patterns include manipulating input data to cause failure conditions or using malformed data to force error states.
• Security Impact:
- Direct consequences include application crashes and denial of service scenarios.
- Potential cascading effects could involve corrupted data, unexpected application behavior, or security breaches if sensitive operations are affected.
- Business impact may include loss of user trust, downtime, and financial damage due to service interruptions or data loss.
• Prevention Guidelines:
- Specific code-level fixes include checking the return value of functions that can return a NULL pointer and handling error conditions appropriately.
- Security best practices involve implementing thorough input validation, error handling, and using assertions to validate pointer integrity before dereferencing.
- Recommended tools and frameworks include static code analysis tools that can flag potential NULL pointer dereference issues and runtime error detection tools for dynamic analysis.
Technical Details
Likelihood of Exploit: Not specified
Affected Languages: C, C++
Affected Technologies: Not specified
Vulnerable Code Example
// vulnerable.c {10-11}
// This code attempts to allocate memory and use it without checking
// whether the memory allocation was successful. If malloc fails, it
// returns NULL, leading to a potential NULL pointer dereference.
#include <stdio.h>
#include <stdlib.h>
void process_data() {
int *data = (int *)malloc(10 * sizeof(int)); // Attempt to allocate memory
// Potentially dereferencing a NULL pointer if malloc fails
data[0] = 42; // Accessing memory without checking if allocation succeeded
printf("Data processed: %d\n", data[0]);
free(data);
}
int main() {
process_data();
return 0;
}
How to fix Unchecked Return Value to NULL Pointer Dereference?
To fix this vulnerability, it's essential to check the return value of functions that can return NULL, such as malloc(). If the allocation fails and returns NULL, the program should handle this situation gracefully. This can be done by logging an error message and terminating the function early. This prevents attempts to dereference a NULL pointer, which can lead to undefined behavior or program crashes.
Implementing a check after the allocation and before using the pointer ensures that the program only proceeds when it has valid memory to work with.
Fixed Code Example
// fixed.c {11-14}
// This code includes a check for NULL after memory allocation.
// If malloc fails, it logs an error message and exits gracefully.
#include <stdio.h>
#include <stdlib.h>
void process_data() {
int *data = (int *)malloc(10 * sizeof(int)); // Attempt to allocate memory
if (data == NULL) { // Check if allocation failed
perror("Failed to allocate memory"); // Log an error message
return; // Exit the function if allocation fails
}
data[0] = 42; // Safe to use the allocated memory
printf("Data processed: %d\n", data[0]);
free(data); // Free the allocated memory
}
int main() {
process_data();
return 0;
}
In the fixed code example, the lines immediately following the memory allocation introduce a check for NULL. If malloc returns NULL, an error message is printed using perror(), and the function exits, preventing any attempt to dereference the NULL pointer. This approach ensures the program is robust against memory allocation failures and adheres to best practices for error handling in C.