CWE-496: Public Data Assigned to Private Array-Typed Field

What is Public Data Assigned to Private Array-Typed Field?

• Overview: Assigning public data to a private array-typed field in object-oriented languages like C, C++, Java, and C# can unintentionally expose or allow modification of that array, compromising the intended encapsulation and security of the data.

• Exploitation Methods:

• Attackers can manipulate or access the data within the private array if public data references it.
• Common attack patterns include intercepting data assignments to the array and modifying the contents through indirect access.

• Security Impact:

• Direct consequences include unauthorized data access and potential data manipulation.
• Potential cascading effects include data integrity issues and increased vulnerability to other attacks.
• Business impact may involve data breaches, loss of customer trust, and legal ramifications due to non-compliance with data protection standards.

• Prevention Guidelines:

• Specific code-level fixes include creating defensive copies of arrays when assigning public data to private fields.
• Security best practices involve maintaining strict encapsulation and using immutable data structures when possible.
• Recommended tools and frameworks include static code analysis tools to detect potential vulnerabilities and adherence to secure coding standards.

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Technical Details

Likelihood of Exploit: Not specified

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

Affected Technologies: Not specified

Vulnerable Code Example

#include <stdio.h>
#include <string.h>

// Structure with a private array
typedef struct {
    char privateData[16];
} SecureContainer;

// Function that improperly assigns public data to the private array
void assignPublicData(SecureContainer *container, const char *publicData) {
    // Vulnerable: Directly assigning public data to a private array
    strncpy(container->privateData, publicData, sizeof(container->privateData));
    container->privateData[sizeof(container->privateData) - 1] = '\0'; // Ensure null-termination
}

int main() {
    SecureContainer container;
    // Public data that could come from an untrusted source
    const char *publicData = "UntrustedSourceData";
    assignPublicData(&container, publicData);
    printf("Private Data: %s\n", container.privateData);
    return 0;
}

Explanation

In this vulnerable code, the function assignPublicData receives public data and assigns it directly to a private array within the SecureContainer struct. This exposes the private array to public manipulation, allowing an attacker to potentially overflow the array or manipulate its contents. Although strncpy is used, it does not prevent the input from being too large for the buffer, leading to potential data truncation and loss of integrity.

How to fix Public Data Assigned to Private Array-Typed Field?

To fix this vulnerability, you should avoid directly assigning public data to private fields. Instead, you can use an intermediate buffer to validate and sanitize the input data before copying it to the private array. By implementing proper boundary checks and sanitization, you can prevent buffer overflow and unauthorized access to private data. Additionally, using functions that enforce buffer limits, like strncpy, with careful handling of null-termination is crucial for secure data handling.

Fixed Code Example

#include <stdio.h>
#include <string.h>

// Structure with a private array
typedef struct {
    char privateData[16];
} SecureContainer;

// Function that safely assigns public data to the private array
void assignPublicData(SecureContainer *container, const char *publicData) {
    // Fixed: Use a temporary buffer to sanitize and validate the input data
    char tempBuffer[16];
    strncpy(tempBuffer, publicData, sizeof(tempBuffer) - 1);
    tempBuffer[sizeof(tempBuffer) - 1] = '\0'; // Ensure null-termination

    // Additional validation can be added here if needed
    // For example, checking for unwanted characters or patterns

    // Safely copy from the validated temporary buffer to the private array
    strncpy(container->privateData, tempBuffer, sizeof(container->privateData) - 1);
    container->privateData[sizeof(container->privateData) - 1] = '\0'; // Ensure null-termination
}

int main() {
    SecureContainer container;
    // Public data that could come from an untrusted source
    const char *publicData = "SafeData";
    assignPublicData(&container, publicData);
    printf("Private Data: %s\n", container.privateData);
    return 0;
}

Explanation

In the fixed code, a temporary buffer (tempBuffer) is used to first copy the public data. This buffer allows for validation and sanitization of the input data before it is assigned to the private array in the SecureContainer. This approach prevents direct exposure of the private array to public data, mitigating the risk of buffer overflows and unauthorized data manipulation. Additionally, the use of a temporary buffer allows for further input validation, ensuring that only safe and expected data is copied to the private array.