CWE - CWE-667: Improper Locking (4.19.1)
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    CWE-667: Improper Locking

    Weakness ID: 667
    Vulnerability Mapping: ALLOWED This CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review (with careful review of mapping notes)
    Abstraction: Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
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    + Description
    The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.
    + Extended Description

    Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

    + Common Consequences
    Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
    Impact Details

    DoS: Resource Consumption (CPU)

    		Scope: Availability

    Inconsistent locking discipline can lead to deadlock.
    + Potential Mitigations
    Phase(s) Mitigation

    Implementation

    Strategy: Libraries or Frameworks

    Use industry standard APIs to implement locking mechanism.
    + Relationships
    Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
    + Relevant to the view "Research Concepts" (View-1000)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 662 Improper Synchronization
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 412 Unrestricted Externally Accessible Lock
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 413 Improper Resource Locking
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 414 Missing Lock Check
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 609 Double-Checked Locking
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 764 Multiple Locks of a Critical Resource
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 765 Multiple Unlocks of a Critical Resource
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 832 Unlock of a Resource that is not Locked
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 833 Deadlock
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 1232 Improper Lock Behavior After Power State Transition
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 1233 Security-Sensitive Hardware Controls with Missing Lock Bit Protection
    ParentOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 1234 Hardware Internal or Debug Modes Allow Override of Locks
    + Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 662 Improper Synchronization
    + Relevant to the view "CISQ Quality Measures (2020)" (View-1305)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 662 Improper Synchronization
    + Relevant to the view "CISQ Data Protection Measures" (View-1340)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 662 Improper Synchronization
    + Modes Of Introduction
    Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
    Phase Note
    Architecture and Design
    Implementation
    + Applicable Platforms
    Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
    Languages

    Class: Not Language-Specific (Undetermined Prevalence)

    Technologies

    Class: Not Technology-Specific (Undetermined Prevalence)

    + Demonstrative Examples

    Example 1


    In the following Java snippet, methods are defined to get and set a long field in an instance of a class that is shared across multiple threads. Because operations on double and long are nonatomic in Java, concurrent access may cause unexpected behavior. Thus, all operations on long and double fields should be synchronized.

    (bad code)
    Example Language: Java 
    private long someLongValue;
    public long getLongValue() {
    return someLongValue;
    }

    public void setLongValue(long l) {
    someLongValue = l;
    }


    Example 2


    This code tries to obtain a lock for a file, then writes to it.

    (bad code)
    Example Language: PHP 
    function writeToLog($message){
    $logfile = fopen("logFile.log", "a");
    //attempt to get logfile lock
    if (flock($logfile, LOCK_EX)) {
    fwrite($logfile,$message);
    // unlock logfile
    flock($logfile, LOCK_UN);
    }
    else {
    print "Could not obtain lock on logFile.log, message not recorded\n";
    }
    }
    fclose($logFile);

    PHP by default will wait indefinitely until a file lock is released. If an attacker is able to obtain the file lock, this code will pause execution, possibly leading to denial of service for other users. Note that in this case, if an attacker can perform an flock() on the file, they may already have privileges to destroy the log file. However, this still impacts the execution of other programs that depend on flock().



    Example 3


    The following function attempts to acquire a lock in order to perform operations on a shared resource.

    (bad code)
    Example Language: C 
    void f(pthread_mutex_t *mutex) {
    pthread_mutex_lock(mutex);

    /* access shared resource */


    pthread_mutex_unlock(mutex);
    }

    However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason, the function may introduce a race condition into the program and result in undefined behavior.

    In order to avoid data races, correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting them to higher levels.

    (good code)
    Example Language: C 
    int f(pthread_mutex_t *mutex) {
    int result;

    result = pthread_mutex_lock(mutex);
    if (0 != result)
    return result;


    /* access shared resource */


    return pthread_mutex_unlock(mutex);
    }


    Example 4


    It may seem that the following bit of code achieves thread safety while avoiding unnecessary synchronization...

    (bad code)
    Example Language: Java 
    if (helper == null) {
    synchronized (this) {
    if (helper == null) {
    helper = new Helper();
    }
    }
    }
    return helper;

    The programmer wants to guarantee that only one Helper() object is ever allocated, but does not want to pay the cost of synchronization every time this code is called.

    Suppose that helper is not initialized. Then, thread A sees that helper==null and enters the synchronized block and begins to execute:

    (bad code)
    Example Language: Java 
    helper = new Helper();

    If a second thread, thread B, takes over in the middle of this call and helper has not finished running the constructor, then thread B may make calls on helper while its fields hold incorrect values.



    + Selected Observed Examples

    Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

    Reference Description
    Chain: improper locking (CWE-667) leads to race condition (CWE-362), as exploited in the wild per CISA KEV.
    Attacker provides invalid address to a memory-reading function, causing a mutex to be unlocked twice
    function in OS kernel unlocks a mutex that was not previously locked, causing a panic or overwrite of arbitrary memory.
    Chain: OS kernel does not properly handle a failure of a function call (CWE-755), leading to an unlock of a resource that was not locked (CWE-832), with resultant crash.
    OS kernel performs an unlock in some incorrect circumstances, leading to panic.
    OS deadlock
    OS deadlock involving 3 separate functions
    deadlock in library
    deadlock triggered by packets that force collisions in a routing table
    read/write deadlock between web server and script
    web server deadlock involving multiple listening connections
    multiple simultaneous calls to the same function trigger deadlock.
    chain: other weakness leads to NULL pointer dereference (CWE-476) or deadlock (CWE-833).
    deadlock when an operation is performed on a resource while it is being removed.
    Deadlock in device driver triggered by using file handle of a related device.
    Deadlock when large number of small messages cannot be processed quickly enough.
    OS kernel has deadlock triggered by a signal during a core dump.
    Race condition leads to deadlock.
    Chain: array index error (CWE-129) leads to deadlock (CWE-833)
    Program can not execute when attacker obtains a mutex.
    Program can not execute when attacker obtains a lock on a critical output file.
    Program can not execute when attacker obtains a lock on a critical output file.
    Critical file can be opened with exclusive read access by user, preventing application of security policy. Possibly related to improper permissions, large-window race condition.
    Chain: predictable file names used for locking, allowing attacker to create the lock beforehand. Resultant from permissions and randomness.
    Chain: Lock files with predictable names. Resultant from randomness.
    Product does not check if it can write to a log file, allowing attackers to avoid logging by accessing the file using an exclusive lock. Overlaps unchecked error condition. This is not quite CWE-412, but close.
    + Weakness Ordinalities
    Ordinality Description
    Primary
    (where the weakness exists independent of other weaknesses)
    + Detection Methods
    Method Details

    Automated Static Analysis
    Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

    Effectiveness: High
    + Memberships
    Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
    Nature Type ID Name
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 748 CERT C Secure Coding Standard (2008) Appendix - POSIX (POS)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 852 The CERT Oracle Secure Coding Standard for Java (2011) Chapter 9 - Visibility and Atomicity (VNA)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 853 The CERT Oracle Secure Coding Standard for Java (2011) Chapter 10 - Locking (LCK)
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 884 CWE Cross-section
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 986 SFP Secondary Cluster: Missing Lock
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1131 CISQ Quality Measures (2016) - Security
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1142 SEI CERT Oracle Secure Coding Standard for Java - Guidelines 08. Visibility and Atomicity (VNA)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1143 SEI CERT Oracle Secure Coding Standard for Java - Guidelines 09. Locking (LCK)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1169 SEI CERT C Coding Standard - Guidelines 14. Concurrency (CON)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1171 SEI CERT C Coding Standard - Guidelines 50. POSIX (POS)
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1401 Comprehensive Categorization: Concurrency
    + Vulnerability Mapping Notes
    Usage ALLOWED-WITH-REVIEW
    (this CWE ID could be used to map to real-world vulnerabilities in limited situations requiring careful review)
    Reason Abstraction

    Rationale

    		This CWE entry is a Class and might have Base-level children that would be more appropriate

    Comments

    		Examine children of this entry to see if there is a better fit
    + Notes

    Maintenance

    Deeper research is necessary for synchronization and related mechanisms, including locks, mutexes, semaphores, and other mechanisms. Multiple entries are dependent on this research, which includes relationships to concurrency, race conditions, reentrant functions, etc. CWE-662 and its children - including CWE-667, CWE-820, CWE-821, and others - may need to be modified significantly, along with their relationships.
    + Taxonomy Mappings
    Mapped Taxonomy Name Node ID Fit Mapped Node Name
    CERT C Secure Coding CON31-C CWE More Abstract Do not destroy a mutex while it is locked
    CERT C Secure Coding POS48-C CWE More Abstract Do not unlock or destroy another POSIX thread's mutex
    The CERT Oracle Secure Coding Standard for Java (2011) VNA00-J Ensure visibility when accessing shared primitive variables
    The CERT Oracle Secure Coding Standard for Java (2011) VNA02-J Ensure that compound operations on shared variables are atomic
    The CERT Oracle Secure Coding Standard for Java (2011) VNA05-J Ensure atomicity when reading and writing 64-bit values
    The CERT Oracle Secure Coding Standard for Java (2011) LCK06-J Do not use an instance lock to protect shared static data
    Software Fault Patterns SFP19 Missing Lock
    OMG ASCSM ASCSM-CWE-667
    + References
    [REF-962] Object Management Group (OMG). "Automated Source Code Security Measure (ASCSM)". ASCSM-CWE-667. 2016-01.
    <http://www.omg.org/spec/ASCSM/1.0/>.
    + Content History
    + Submissions
    Submission Date Submitter Organization
    2008-04-11
    (CWE Draft 9, 2008-04-11)     		CWE Content Team MITRE
    + Modifications
    Modification Date Modifier Organization
    2025-12-11
    (CWE 4.19, 2025-12-11)     		CWE Content Team MITRE
    updated Applicable_Platforms, Weakness_Ordinalities
    2025-04-03
    (CWE 4.17, 2025-04-03)     		CWE Content Team MITRE
    updated Demonstrative_Examples
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes
    2023-04-27 CWE Content Team MITRE
    updated Detection_Factors, Relationships
    2023-01-31 CWE Content Team MITRE
    updated Description
    2022-06-28 CWE Content Team MITRE
    updated Observed_Examples
    2021-03-15 CWE Content Team MITRE
    updated Demonstrative_Examples
    2020-12-10 CWE Content Team MITRE
    updated Relationships
    2020-08-20 CWE Content Team MITRE
    updated Relationships
    2020-02-24 CWE Content Team MITRE
    updated Relationships, Type
    2019-09-23 CWE Content Team MITRE
    updated Description, Maintenance_Notes, Relationships
    2019-09-19 CWE Content Team MITRE
    updated Relationships
    2019-01-03 CWE Content Team MITRE
    updated References, Relationships, Taxonomy_Mappings
    2017-11-08 CWE Content Team MITRE
    updated Taxonomy_Mappings
    2017-05-03 CWE Content Team MITRE
    updated Related_Attack_Patterns
    2014-07-30 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2012-10-30 CWE Content Team MITRE
    updated Potential_Mitigations
    2012-05-11 CWE Content Team MITRE
    updated Demonstrative_Examples, Observed_Examples, Relationships
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences, Relationships, Taxonomy_Mappings
    2010-12-13 CWE Content Team MITRE
    updated Description, Name, Relationships
    2010-09-27 CWE Content Team MITRE
    updated Relationships
    2009-07-27 CWE Content Team MITRE
    updated Common_Consequences
    2009-05-27 CWE Content Team MITRE
    updated Relationships
    2009-03-10 CWE Content Team MITRE
    updated Related_Attack_Patterns
    2008-11-24 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2008-09-08 CWE Content Team MITRE
    updated Relationships
    2008-07-01 Eric Dalci Cigital
    updated Potential_Mitigations, Time_of_Introduction
    2008-07-01 Sean Eidemiller Cigital
    added/updated demonstrative examples
    + Previous Entry Names
    Change Date Previous Entry Name
    2010-12-13 Insufficient Locking
    Page Last Updated: January 21, 2026