CWE-1420: Exposure of Sensitive Information during Transient Execution

What is Exposure of Sensitive Information during Transient Execution?

• Overview: Exposure of Sensitive Information during Transient Execution is a vulnerability where a processor temporarily executes incorrect or speculative operations that do not commit to the architectural state, potentially revealing sensitive data through covert channels such as data caches.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting code sequences that leak data through covert channels during transient execution.
• Attackers may trigger transient execution by causing branch prediction errors or handling exceptions after younger operations execute.
• Common attack patterns include timing or power analysis to infer data accessed during transient operations.

• Security Impact:

• Direct consequences include unauthorized access to sensitive data such as passwords or cryptographic keys.
• Potential cascading effects include further breaches of system integrity and confidentiality.
• Business impact could involve data breaches, loss of customer trust, and potential legal repercussions.

• Prevention Guidelines:

• Specific code-level fixes include avoiding code patterns that are susceptible to branch prediction errors.
• Implement security best practices such as constant-time programming to reduce timing discrepancies.
• Use recommended tools and frameworks like compiler mitigations and updated processor microcode to minimize risk.

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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 os

def read_sensitive_file(filename):
    # Vulnerable to speculative execution attacks
    # An attacker might exploit CPU's transient execution to access sensitive data
    with open(filename, 'r') as file:
        return file.read()  # Directly returning sensitive data

In this example, the function read_sensitive_file reads a sensitive file and directly returns its content. This approach is vulnerable because during speculative execution, an attacker might exploit the CPU's transient execution paths to infer sensitive data before the execution is finalized, potentially exposing the file's contents.

How to fix Exposure of Sensitive Information during Transient Execution?

To mitigate the risk of exposure of sensitive information during transient execution, you should:

1. Avoid returning sensitive data directly from functions.
2. Use access controls and ensure sensitive operations are performed in secure contexts.
3. Mask or sanitize sensitive data before it's exposed to any execution paths that could be speculatively executed.
4. Implement CPU-level mitigations such as disabling certain speculative execution features if supported by the hardware.

In the fixed example, we will ensure that sensitive data isn't directly returned and is processed in a way that speculative execution does not inadvertently expose it.

Fixed Code Example

import os

def read_sensitive_file_secure(filename):
    # Securely read the file to mitigate speculative execution attacks
    with open(filename, 'r') as file:
        data = file.read()  # Read the file content into a local variable

    # Process the data securely, ensuring only non-sensitive information is exposed
    processed_data = process_data_securely(data)  # Mask or sanitize data
    return processed_data  # Return only non-sensitive information

def process_data_securely(data):
    # Example of sanitizing sensitive data
    # Implement logic to ensure only safe-to-disclose data is returned
    # For example, extract only non-sensitive summary or metadata
    return "Processed data summary"  # Placeholder: Replace with actual logic

In the fixed example, we introduced a function process_data_securely that processes the data before returning it. This ensures that any sensitive information is masked or sanitized, reducing the risk of exposure during transient execution. The key is to ensure that the data returned is safe and doesn't expose sensitive content that could be speculatively executed by an attacker.