CWE-1265: Unintended Reentrant Invocation of Non-reentrant Code Via Nested Calls

What is Unintended Reentrant Invocation of Non-reentrant Code Via Nested Calls?

• Overview: This vulnerability occurs when non-reentrant code, which is not designed to be safely re-entered before the previous execution is complete, is unintentionally invoked again through nested calls, potentially altering shared state and leading to unpredictable behavior.

• Exploitation Methods:

• Attackers can exploit this vulnerability by manipulating inputs or using scripts to trigger specific control flows that cause the non-reentrant code to be re-invoked.
• Common attack patterns involve inducing nested calls through external inputs, often in environments like web browsers or PDF readers, where the code execution path can be influenced by user actions or untrusted scripts.

• Security Impact:

• Direct consequences include data corruption, unexpected behavior, or crashes due to shared state being altered.
• Potential cascading effects can lead to application instability or security breaches if sensitive operations are impacted.
• Business impact may involve service downtime, loss of data integrity, or compromised customer trust.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that non-reentrant code is protected by locks or is otherwise designed to be reentrant.
• Security best practices involve thorough code reviews and testing to detect and address reentrancy issues, especially in complex systems with multiple execution paths.
• Recommended tools and frameworks include static analysis tools to detect potential reentrancy vulnerabilities and development frameworks that provide safety mechanisms for concurrency control.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

JavaScript Example

// This function is intended to manage a critical process
// It incorrectly allows reentrant calls by calling itself indirectly
function processManager() {
    console.log("Starting critical process...");
    criticalSection(); // Start of non-reentrant code
    console.log("Critical process completed.");
}

function criticalSection() {
    // Non-reentrant critical section of code
    console.log("Executing critical section.");
    // Vulnerability: unintended reentrant invocation
    // This indirect call can lead to nested invocation of the non-reentrant code
    if (Date.now() % 2 === 0) { // Random condition for demonstration
        processManager(); // Unintended reentrant call
    }
}

Explanation

In the above vulnerable code example, the criticalSection function, which is intended to be non-reentrant, inadvertently calls processManager under certain conditions. This leads to a nested invocation of criticalSection, which can cause unexpected behavior or data corruption if the critical section manipulates shared state or resources.

How to fix Unintended Reentrant Invocation of Non-reentrant Code Via Nested Calls?

To fix this issue, we must prevent the critical section from being entered more than once at the same time. This can be achieved by implementing a reentrancy guard using a state flag or lock mechanism.

Fix Approach:

1. Use a Reentrancy Guard: Implement a flag to check if the critical section is already being executed. If it is, the function should return immediately and not proceed with the execution.
2. Avoid Self-calls: Ensure that functions do not inadvertently call themselves directly or indirectly when they are meant to be non-reentrant.

Fixed Code Example

// Fixed code with implemented reentrancy guard
let isProcessing = false; // Reentrancy guard flag

function processManager() {
    console.log("Starting critical process...");
    criticalSection(); // Start of non-reentrant code
    console.log("Critical process completed.");
}

function criticalSection() {
    // Check if already processing to prevent reentrancy
    if (isProcessing) {
        console.log("Reentrant call detected, aborting.");
        return; // Prevent reentrant execution
    }

    isProcessing = true; // Set guard before entering critical section
    try {
        console.log("Executing critical section.");
        // Critical code that shouldn't be reentrant goes here
        // Ensure no self-calls or indirect calls that could re-enter criticalSection
    } finally {
        isProcessing = false; // Reset guard after execution completes
    }
}

Explanation

In the fixed code example, a isProcessing flag is introduced to manage the state of the critical section execution. Before entering the critical section, the code checks this flag to ensure the function is not already executing. If it is, the function exits early, preventing reentrant execution. This ensures that the critical section adheres to the single-entry principle, avoiding unintended nested calls and potential data corruption or race conditions.