CWE-226: Sensitive Information in Resource Not Removed Before Reuse

What is Sensitive Information in Resource Not Removed Before Reuse?

• Overview: Sensitive Information in Resource Not Removed Before Reuse (CWE-226) occurs when a software application releases a resource such as memory or a file without clearing the sensitive data it contains, thereby allowing the data to be accessed by other processes or entities when the resource is reused.

• Exploitation Methods:

• Attackers can exploit this vulnerability by accessing memory or file resources that have been released but not cleared, potentially recovering sensitive data.
• Common attack patterns include memory scraping, where attackers scan memory for sensitive data, and file recovery attacks, where deleted files are restored and inspected.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive information such as passwords, cryptographic keys, or personal data.
• Potential cascading effects could involve privilege escalation if sensitive credentials are obtained or data breaches if personal or corporate data is exposed.
• Business impact includes reputational damage, legal liabilities, and financial losses due to data breaches or regulatory non-compliance.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that sensitive data is overwritten with zeros or random data before memory or file resources are released.
• Security best practices involve consistently implementing data sanitization routines and ensuring that all data structures are properly cleared before reuse.
• Recommended tools and frameworks include using secure coding libraries and static analysis tools to identify and mitigate instances where sensitive information is not properly cleared from resources.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

import tempfile

def process_sensitive_data(data):
    # Create a temporary file without clearing sensitive data before deletion
    temp_file = tempfile.NamedTemporaryFile(delete=False)
    try:
        temp_file.write(data.encode())  # Writing sensitive data to the file
        temp_file.flush()  # Ensure data is written to disk
        # Some operations on the data
    finally:
        temp_file.close()  # File closed but sensitive data not cleared
        # File is left undeleted and contains sensitive information

Explanation

• Lines {8-13}: This code creates a temporary file and writes sensitive data to it. However, the file is not deleted automatically due to delete=False, and the sensitive data is not cleared or overwritten before the file is closed and left on disk. This can lead to sensitive information being exposed if the file is accessed by unauthorized users.

How to fix Sensitive Information in Resource Not Removed Before Reuse?

To properly fix this vulnerability, it is important to ensure that sensitive data is removed before any resource such as a file is made available for reuse or is left undeleted. The data should be explicitly cleared from memory or the file before it is closed and deleted. This can be achieved by overwriting the data with non-sensitive data before closing the file, and ensuring that the file is deleted securely.

Fixed Code Example

import tempfile
import os

def process_sensitive_data(data):
    # Create a temporary file with automatic deletion and data clearing
    temp_file = tempfile.NamedTemporaryFile(delete=False)
    try:
        temp_file.write(data.encode())  # Writing sensitive data to the file
        temp_file.flush()  # Ensure data is written to disk
        # Some operations on the data
    finally:
        try:
            # Overwriting the file content before deletion
            temp_file.seek(0)
            temp_file.write(b'\x00' * len(data))  # Overwrite with null bytes
            temp_file.flush()
        finally:
            temp_file.close()
            os.unlink(temp_file.name)  # Securely delete the file

Explanation

• Lines {8-20}: In this fixed code, before closing the file, we overwrite the sensitive data with null bytes (or any non-sensitive data) to ensure it is not recoverable. We then flush the file to ensure the overwrite is written to disk. Finally, the file is securely deleted using os.unlink(), ensuring that no sensitive information remains on disk after the file is closed. This approach helps mitigate the risk of sensitive data being exposed if the temporary file is accessed by unauthorized entities.