CWE-414: Missing Lock Check

What is Missing Lock Check?

• Overview:

• CWE-414, Missing Lock Check, occurs when a software product fails to verify the presence of a lock before performing sensitive operations on a resource, potentially leading to race conditions or data corruption.

• Exploitation Methods:

• Attackers can exploit this vulnerability by accessing shared resources simultaneously, leading to inconsistent state or unauthorized access.
• Common attack patterns include manipulating the timing of operations to interfere with the expected sequence of execution, thereby gaining unintended control or accessing restricted data.

• Security Impact:

• Direct consequences of successful exploitation include data corruption, unauthorized data access, or application crashes.
• Potential cascading effects involve broader system instability, compromised data integrity, and unauthorized escalation of privileges.
• Business impact can include loss of customer trust, financial loss due to data breaches, and legal consequences due to non-compliance with data protection regulations.

• Prevention Guidelines:

• Specific code-level fixes include implementing proper locking mechanisms such as mutexes or semaphores to ensure exclusive access to shared resources.
• Security best practices involve conducting thorough code reviews and testing to identify and eliminate race conditions and ensuring consistent use of locks across all code paths.
• Recommended tools and frameworks include static analysis tools for detecting potential race conditions and using concurrency-safe libraries to handle shared resources securely.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import threading

class FileHandler:
    def __init__(self):
        self.file = None
        self.lock = threading.Lock()

    def open_file(self, filename):
        # Vulnerable: Missing lock check before file operation
        if self.file is None:
            # Multiple threads can reach this point simultaneously, leading to race conditions
            self.file = open(filename, 'w')  
            print(f"File {filename} opened for writing.")

    def close_file(self):
        if self.file is not None:
            self.file.close()
            self.file = None
            print("File closed.")

Explanation:

• The open_file method lacks synchronization, allowing multiple threads to potentially open the file at the same time.
• This can lead to race conditions where two or more threads check self.file simultaneously and attempt to open the file, causing unpredictable behavior or data corruption.

How to fix Missing Lock Check?

To fix the missing lock check vulnerability, ensure that the lock is acquired before any file operations are performed. This ensures thread safety by allowing only one thread to execute the critical section at a time, thus preventing race conditions.

Fixed Code Example

import threading

class FileHandler:
    def __init__(self):
        self.file = None
        self.lock = threading.Lock()

    def open_file(self, filename):
        # Fixed: Acquire lock to ensure only one thread can perform the file operation
        with self.lock:
            if self.file is None:
                self.file = open(filename, 'w')
                print(f"File {filename} opened for writing.")

    def close_file(self):
        # Ensure file closure is also protected by the lock
        with self.lock:
            if self.file is not None:
                self.file.close()
                self.file = None
                print("File closed.")

Explanation:

• The open_file method now uses a with self.lock context manager to ensure mutual exclusion, meaning only one thread can open the file at a time.
• This prevents race conditions by ensuring that the check and the subsequent file operation are atomic.
• Similarly, the close_file method is protected by the lock to ensure safe file closure, maintaining consistent state across threads.