CWE-672: Operation on a Resource after Expiration or Release

What is Operation on a Resource after Expiration or Release?

• Overview: This vulnerability occurs when a program continues to use, access, or operate on a resource that has been expired, released, or revoked, which can lead to unexpected behavior or security issues.

• Exploitation Methods:

• Attackers can exploit this vulnerability by manipulating the program to perform operations on resources that should no longer be available.
• Common attack patterns include inducing the program to reference deallocated memory, access closed files, or use expired authentication tokens.

• Security Impact:

• Direct consequences of successful exploitation include program crashes, data corruption, and unauthorized access to sensitive information.
• Potential cascading effects involve broader system instability, privilege escalation, or denial of service.
• Business impact can range from loss of customer trust to financial losses due to data breaches or system outages.

• Prevention Guidelines:

• Specific code-level fixes include implementing proper checks to ensure resources are still valid before use and freeing resources only when they are no longer needed.
• Security best practices involve rigorous resource management, including proper initialization, timely release, and avoiding reuse of expired resources.
• Recommended tools and frameworks include static analysis tools to detect resource mishandling and runtime analysis tools to monitor resource lifecycle management.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Mobile

Vulnerable Code Example

class ResourceHandler:
    def __init__(self):
        self.file = open('data.txt', 'r')  # Open file in read mode

    def read_data(self):
        data = self.file.read()  # Read data from the file
        self.file.close()  # Close the file after reading
        return data

    def process_data(self):
        # Attempt to read from the file again, which is already closed
        return self.file.read()  # This will raise a ValueError as the file is closed

Explanation:

In this example, the ResourceHandler class opens a file when an instance is created. The read_data method reads the file content and closes it. However, the process_data method tries to read from the file again after it has been closed, leading to an error. This demonstrates an operation on a resource after it has been released, which is a common mistake that can cause runtime errors.

How to fix Operation on a Resource after Expiration or Release?

To fix this issue, ensure that resources are accessed only while they are valid and open. In Python, using context managers (the with statement) is a best practice for managing resources like files, as they automatically handle the opening and closing of the resource, preventing access after it has been released.

Fixed Code Example

class ResourceHandler:
    def __init__(self, filename):
        self.filename = filename  # Store the filename for reuse

    def read_data(self):
        # Use a context manager to safely open and read the file
        with open(self.filename, 'r') as file:
            data = file.read()  # Read data within the context
        return data  # File is automatically closed when exiting the block

    def process_data(self):
        # Use a context manager again to ensure safe access to the file
        with open(self.filename, 'r') as file:
            return file.read()  # Read data safely within the context

Explanation:

In the fixed code, both read_data and process_data methods use a context manager (with statement) to handle file operations. This ensures the file is opened, read, and closed properly within the context, and prevents any operations on the file after it has been closed. This pattern guarantees that the resource is managed correctly, avoiding operations on a resource after it has been released.