What is Multiple Locks of a Critical Resource (CWE-764)?

TL;DR: Multiple Locks of a Critical Resource (CWE-764) is an issue where software acquires more locks than intended on critical resources, leading to unexpected states. Proper synchronization and timely lock releases are essential fixes.

What is Multiple Locks of a Critical Resource?

Multiple Locks of a Critical Resource (CWE-764) is an issue where software locks a critical resource more times than intended, leading to unexpected states in the system. As defined by the MITRE Corporation under CWE-764 and classified by the OWASP Foundation under [mapping], this vulnerability can cause significant disruptions.

Quick Summary

Multiple Locks of a Critical Resource (CWE-764) is an issue where software locks a critical resource more times than intended, leading to unexpected states in the system. This can result in denial-of-service due to resource consumption and crashes, compromising system integrity and availability. Jump to: Overview · How It Works · Business Impact · Attack Scenario · Detection · Fixes · Framework-Specific Fixes · Ask AI

Jump to: Quick Summary · Multiple Locks of a Critical Resource Overview · How Multiple Locks of a Critical Resource Works · Business Impact of Multiple Locks of a Critical Resource · Multiple Locks of a Critical Resource Attack Scenario · How to Detect Multiple Locks of a Critical Resource · How to Fix Multiple Locks of a Critical Resource · Framework-Specific Fixes for Multiple Locks of a Critical Resource · How to Ask AI to Check Your Code for Multiple Locks of a Critical Resource · Multiple Locks of a Critical Resource Best Practices Checklist · Multiple Locks of a Critical Resource FAQ · Vulnerabilities Related to Multiple Locks of a Critical Resource · References · Scan Your Own Site

Multiple Locks of a Critical Resource Overview

What

Multiple Locks of a Critical Resource (CWE-764) is an issue where software locks a critical resource more times than intended, leading to unexpected states.

Why it matters

This can result in denial-of-service due to resource consumption and crashes, compromising system integrity and availability.

Where it occurs

It commonly occurs in multi-threaded applications or systems with shared resources managed through synchronization mechanisms like mutexes or semaphores.

Who is affected

Developers working on multi-threaded applications or systems managing critical resources are at risk of encountering this issue.

Who is NOT affected

Applications that do not manage critical resources through locking mechanisms or those employing robust resource management strategies are less likely to be impacted.

How Multiple Locks of a Critical Resource Works

Root Cause

The root cause lies in the improper handling of locks on critical resources, leading to multiple acquisitions without proper releases.

Attack Flow

1. The attacker identifies a code path that improperly handles lock acquisition.
2. The software acquires more locks than intended on a critical resource.
3. This leads to unexpected states and potential crashes or hangs.
4. System integrity is compromised due to inconsistent state transitions.

Prerequisites to Exploit

• Code must have multiple paths leading to lock acquisitions without corresponding releases.
• Lack of proper error handling that ensures timely release of locks.

Vulnerable Code

public void performTask() {
    synchronized(lock) {
        // Perform task
        if (someCondition) {
            performAnotherTask();
        }
    }
}

This code acquires a lock but does not ensure it is released under all conditions, leading to potential multiple locks.

Secure Code

public void performTask() {
    synchronized(lock) {
        // Perform task
        if (someCondition) {
            try {
                performAnotherTask();
            } finally {
                lock.release();  // Ensure the lock is released even on exceptions
            }
        }
    }
}

The secure code ensures that locks are properly managed and released under all circumstances.

Business Impact of Multiple Locks of a Critical Resource

Availability

• Resource Consumption: Excessive locking can lead to resource starvation.
• Crashes: Unexpected states may cause application crashes or hangs, disrupting service availability.

Integrity

• Data Corruption: Inconsistent state transitions due to improper synchronization can corrupt data integrity.

Business Consequences

• Financial losses from downtime and recovery efforts.
• Compliance issues due to unavailability of critical systems.
• Reputational damage from service disruptions impacting customer trust.

Multiple Locks of a Critical Resource Attack Scenario

1. The attacker identifies code paths where locks are improperly managed, leading to multiple acquisitions without corresponding releases.
2. This results in unexpected states and potential crashes or hangs within the system.
3. System availability is compromised due to resource starvation and application instability.
4. Data integrity is affected as inconsistent state transitions lead to data corruption.

How to Detect Multiple Locks of a Critical Resource

Manual Testing

• Check for multiple lock acquisitions: Review code paths where locks are acquired but not properly released under all conditions.
• Verify error handling: Ensure that locks are released even in the presence of exceptions or errors.

Automated Scanners (SAST/DAST)

Static analysis tools can detect improper synchronization patterns, while dynamic testing can identify actual runtime issues due to multiple lock acquisitions.

PenScan Detection

PenScan’s scanner engines such as ZAP and Wapiti can help identify instances where locks are improperly managed in the codebase.

False Positive Guidance

A false positive may occur if a pattern looks risky but is actually safe due to context that a static analysis tool cannot determine. Ensure proper manual review of findings for accuracy.

How to Fix Multiple Locks of a Critical Resource

• Ensure timely lock release: Implement proper error handling and ensure locks are released under all conditions.
• Use try-with-resources: Employ language-specific constructs like Java’s try-with-resources for automatic resource management.
• Review control paths: Ensure that all code paths through which resources are locked correspond to exactly as many unlocks.

Framework-Specific Fixes for Multiple Locks of a Critical Resource

Java

public void performTask() {
    synchronized(lock) {
        // Perform task
        if (someCondition) {
            try {
                performAnotherTask();
            } finally {
                lock.release();  // Ensure the lock is released even on exceptions
            }
        }
    }
}

Python/Django

def perform_task():
    with some_lock:
        # Perform task
        if some_condition:
            try:
                perform_another_task()
            except Exception as e:
                raise e  # Ensure the lock is released even on exceptions

How to Ask AI to Check Your Code for Multiple Locks of a Critical Resource

public void performTask() {
    synchronized(lock) {
        // Perform task
        if (someCondition) {
            performAnotherTask();
        }
    }
}

Multiple Locks of a Critical Resource Best Practices Checklist

• ✅ Ensure timely lock release under all conditions.
• ✅ Use try-with-resources for automatic resource management.
• ✅ Review control paths to ensure proper synchronization.
• ✅ Implement robust error handling mechanisms.
• ✅ Regularly audit code for improper locking patterns.

Multiple Locks of a Critical Resource FAQ

How does multiple locks on a critical resource occur?

It occurs when a software component acquires a lock more times than intended, leading to unexpected states or conditions in the system.

What are the consequences of Multiple Locks of a Critical Resource?

This can result in denial-of-service (DoS) due to resource consumption and crashes, as well as unexpected state transitions that compromise integrity and availability.

How do you detect multiple locks on critical resources?

Detect it through manual code reviews focusing on synchronization mechanisms or using automated static analysis tools designed for identifying improper locking patterns.

Can you provide an example of vulnerable code in Python?

In Python, a function that acquires a lock and then waits indefinitely without releasing the lock can lead to this issue.

What is the impact on system integrity when multiple locks occur?

It can cause data corruption or unexpected state changes, leading to inconsistent application behavior.

How does one prevent multiple locks of critical resources in Java applications?

Ensure that all control paths through the code where a resource is locked correspond to exactly as many unlocks. Use try-with-resources for automatic lock management.

What are common mitigation strategies for this issue?

Implement proper synchronization, ensure timely release of locks, and handle exceptional conditions without leaving locks held.

Vulnerabilities Related to Multiple Locks of a Critical Resource

References

• MITRE - CWE-764
• NVD
• NVD

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Multiple Locks of a Critical Resource and other risks before an attacker does.