CWE-805: Buffer Access with Incorrect Length Value
Learn about CWE-805 (Buffer Access with Incorrect Length Value), its security impact, exploitation methods, and prevention guidelines.
What is Buffer Access with Incorrect Length Value?
• Overview: Buffer Access with Incorrect Length Value (CWE-805) occurs when a program accesses a buffer using a length value that exceeds the buffer's actual size, potentially leading to accessing memory outside the intended bounds.
• Exploitation Methods:
- Attackers can exploit this vulnerability by providing input that causes the program to read or write data outside of the allocated buffer space.
- Common attack patterns include buffer overflow attacks, where excess data overwrites adjacent memory, potentially allowing code execution or data corruption.
• Security Impact:
- Direct consequences include program crashes, data corruption, or unauthorized code execution.
- Potential cascading effects include system instability, unauthorized access to sensitive data, or further exploitation through injected malicious code.
- Business impact may involve data breaches, loss of customer trust, legal liabilities, and financial costs related to incident response and remediation.
• Prevention Guidelines:
- Specific code-level fixes include validating length values against buffer sizes before performing read/write operations and using safer functions that automatically handle buffer lengths.
- Security best practices involve adopting secure coding standards, conducting thorough code reviews, and employing static analysis tools to detect buffer misuse.
- Recommended tools and frameworks include compiler options like stack protection, runtime protection mechanisms like address space layout randomization (ASLR), and using languages or libraries that manage memory automatically to reduce manual buffer handling errors.
Technical Details
Likelihood of Exploit:
Affected Languages: C, C++, Assembly
Affected Technologies: Not specified
Vulnerable Code Example
C Example for CWE-805: Buffer Access with Incorrect Length Value
#include <stdio.h>
#include <string.h>
void process_input(const char *input) {
char buffer[10];
// Vulnerable: Using strlen(input) as length may cause buffer overflow
strncpy(buffer, input, strlen(input)); // Incorrect length can exceed buffer size
buffer[9] = '\0'; // Attempt to null-terminate, but buffer may overflow before this line
printf("Processed input: %s\n", buffer);
}
int main() {
const char *user_input = "This is a very long input that can cause problems";
process_input(user_input);
return 0;
}
Explanation of the Vulnerability
In this code, the vulnerability arises from using strlen(input) as the length parameter in strncpy(). If input is longer than the buffer size (10 bytes in this example), strncpy() will attempt to copy more data than the buffer can hold. This results in a buffer overflow, potentially overwriting adjacent memory, leading to undefined behavior, crashes, or security vulnerabilities.
How to fix Buffer Access with Incorrect Length Value?
To fix this vulnerability, ensure that the length parameter passed to strncpy() does not exceed the buffer's capacity. Additionally, always null-terminate the string manually if strncpy() does not null-terminate it (this happens if the source string is longer than the specified length). Use sizeof(buffer) - 1 to ensure there's space for the null terminator, and explicitly set the last character to \0 to avoid relying on strncpy() for null-termination.
Fixed Code Example
#include <stdio.h>
#include <string.h>
void process_input(const char *input) {
char buffer[10];
// Fixed: Limit copy size to buffer capacity minus space for null-terminator
strncpy(buffer, input, sizeof(buffer) - 1); // Copy at most 9 characters
buffer[sizeof(buffer) - 1] = '\0'; // Explicitly null-terminate
printf("Processed input: %s\n", buffer);
}
int main() {
const char *user_input = "This is a very long input that can cause problems";
process_input(user_input);
return 0;
}
Explanation of the Fix
In the fixed code, strncpy() is called with sizeof(buffer) - 1 to ensure that only the first 9 characters are copied into the buffer, leaving room for the null terminator. The line buffer[sizeof(buffer) - 1] = '\0'; explicitly sets the last character of the buffer to \0, ensuring that the string is always null-terminated. This approach prevents buffer overflow and ensures safe string handling by adhering to the buffer's capacity.