The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc.
A race condition violates these properties, which are closely related:

Exclusivity - the code sequence is given exclusive access to the shared resource, i.e., no other code sequence can modify properties of the shared resource before the original sequence has completed execution.
Atomicity - the code sequence is behaviorally atomic, i.e., no other thread or process can concurrently execute the same sequence of instructions (or a subset) against the same resource.

A race condition exists when an "interfering code sequence" can still access the shared resource, violating exclusivity.
The interfering code sequence could be "trusted" or "untrusted." A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Primary

Resultant

Race Condition

Architecture and Design

Implementation
Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single "x++" statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x).

Medium

Availability
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)
DoS: Resource Consumption (Other)
When a race condition makes it possible to bypass a resource cleanup routine or trigger multiple initialization routines, it may lead to resource exhaustion.

Availability
DoS: Crash, Exit, or Restart
DoS: Instability
When a race condition allows multiple control flows to access a resource simultaneously, it might lead the product(s) into unexpected states, possibly resulting in a crash.

Confidentiality
Integrity
Read Files or Directories
Read Application Data
When a race condition is combined with predictable resource names and loose permissions, it may be possible for an attacker to overwrite or access confidential data (CWE-59).

Access Control
Execute Unauthorized Code or Commands
Gain Privileges or Assume Identity
Bypass Protection Mechanism
This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider.

Black Box
Black box methods may be able to identify evidence of race conditions via methods such as multiple simultaneous connections, which may cause the software to become instable or crash. However, race conditions with very narrow timing windows would not be detectable.

White Box
Common idioms are detectable in white box analysis, such as time-of-check-time-of-use (TOCTOU) file operations (CWE-367), or double-checked locking (CWE-609).

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
Race conditions may be detected with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence of any unexpected behavior.
Insert breakpoints or delays in between relevant code statements to artificially expand the race window so that it will be easier to detect.

Moderate

Automated Static Analysis - Binary or Bytecode

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Bytecode Weakness Analysis - including disassembler + source code weakness analysis

Cost effective for partial coverage:

Binary Weakness Analysis - including disassembler + source code weakness analysis

High

Dynamic Analysis with Automated Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Web Application Scanner
Web Services Scanner
Database Scanners

SOAR Partial

Dynamic Analysis with Manual Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Framework-based Fuzzer

Cost effective for partial coverage:

Fuzz Tester
Monitored Virtual Environment - run potentially malicious code in sandbox / wrapper / virtual machine, see if it does anything suspicious

High

Manual Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Manual Source Code Review (not inspections)

Cost effective for partial coverage:

Focused Manual Spotcheck - Focused manual analysis of source

High

Automated Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Source code Weakness Analyzer
Context-configured Source Code Weakness Analyzer

High

Architecture or Design Review

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

High

Architecture and Design
In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.

Architecture and Design
Use thread-safe capabilities such as the data access abstraction in Spring.

Architecture and Design

Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Implementation
When using multithreading and operating on shared variables, only use thread-safe functions.

Implementation
Use atomic operations on shared variables. Be wary of innocent-looking constructs such as "x++". This may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read, followed by a computation, followed by a write.

Implementation
Use a mutex if available, but be sure to avoid related weaknesses such as CWE-412.

Implementation
Avoid double-checked locking (CWE-609) and other implementation errors that arise when trying to avoid the overhead of synchronization.

Implementation
Disable interrupts or signals over critical parts of the code, but also make sure that the code does not go into a large or infinite loop.

Implementation
Use the volatile type modifier for critical variables to avoid unexpected compiler optimization or reordering. This does not necessarily solve the synchronization problem, but it can help.

Architecture and Design
Operation
Environment Hardening
Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

This code could be used in an e-commerce application that supports transfers between accounts. It takes the total amount of the transfer, sends it to the new account, and deducts the amount from the original account.

$transfer_amount = GetTransferAmount();$balance = GetBalanceFromDatabase();
if ($transfer_amount < 0) {FatalError("Bad Transfer Amount");}$newbalance = $balance - $transfer_amount;if (($balance - $transfer_amount) < 0) {FatalError("Insufficient Funds");}SendNewBalanceToDatabase($newbalance);NotifyUser("Transfer of $transfer_amount succeeded.");NotifyUser("New balance: $newbalance");

A race condition could occur between the calls to GetBalanceFromDatabase() and SendNewBalanceToDatabase().
Suppose the balance is initially 100.00. An attack could be constructed as follows:

In the following pseudocode, the attacker makes two simultaneous calls of the program, CALLER-1 and CALLER-2. Both callers are for the same user account.CALLER-1 (the attacker) is associated with PROGRAM-1 (the instance that handles CALLER-1). CALLER-2 is associated with PROGRAM-2.CALLER-1 makes a transfer request of 80.00.PROGRAM-1 calls GetBalanceFromDatabase and sets $balance to 100.00PROGRAM-1 calculates $newbalance as 20.00, then calls SendNewBalanceToDatabase().Due to high server load, the PROGRAM-1 call to SendNewBalanceToDatabase() encounters a delay.CALLER-2 makes a transfer request of 1.00.PROGRAM-2 calls GetBalanceFromDatabase() and sets $balance to 100.00. This happens because the previous PROGRAM-1 request was not processed yet.PROGRAM-2 determines the new balance as 99.00.After the initial delay, PROGRAM-1 commits its balance to the database, setting it to 20.00.PROGRAM-2 sends a request to update the database, setting the balance to 99.00

At this stage, the attacker should have a balance of 19.00 (due to 81.00 worth of transfers), but the balance is 99.00, as recorded in the database.
To prevent this weakness, the programmer has several options, including using a lock to prevent multiple simultaneous requests to the web application, or using a synchronization mechanism that includes all the code between GetBalanceFromDatabase() and SendNewBalanceToDatabase().

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

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.

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);
}

Suppose a processor's Memory Management Unit (MMU) has 5 other shadow MMUs to distribute its workload for its various cores. Each MMU has the start address and end address of "accessible" memory. Any time this accessible range changes (as per the processor's boot status), the main MMU sends an update message to all the shadow MMUs.
Suppose the interconnect fabric does not prioritize such "update" packets over other general traffic packets. This introduces a race condition. If an attacker can flood the target with enough messages so that some of those attack packets reach the target before the new access ranges gets updated, then the attacker can leverage this scenario.

CVE-2022-29527
Go application for cloud management creates a world-writable sudoers file that allows local attackers to inject sudo rules and escalate privileges to root by winning a race condition.
https://www.cve.org/CVERecord?id=CVE-2022-29527

CVE-2021-1782
Chain: improper locking (CWE-667) leads to race condition (CWE-362), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-1782

CVE-2021-0920
Chain: mobile platform race condition (CWE-362) leading to use-after-free (CWE-416), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-0920

CVE-2020-6819
Chain: race condition (CWE-362) leads to use-after-free (CWE-416), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-6819

CVE-2019-18827
chain: JTAG interface is not disabled (CWE-1191) during ROM code execution, introducing a race condition (CWE-362) to extract encryption keys
https://www.cve.org/CVERecord?id=CVE-2019-18827

CVE-2019-1161
Chain: race condition (CWE-362) in anti-malware product allows deletion of files by creating a junction (CWE-1386) and using hard links during the time window in which a temporary file is created and deleted.
https://www.cve.org/CVERecord?id=CVE-2019-1161

CVE-2015-1743
TOCTOU in sandbox process allows installation of untrusted browser add-ons by replacing a file after it has been verified, but before it is executed
https://www.cve.org/CVERecord?id=CVE-2015-1743

CVE-2014-8273
Chain: chipset has a race condition (CWE-362) between when an interrupt handler detects an attempt to write-enable the BIOS (in violation of the lock bit), and when the handler resets the write-enable bit back to 0, allowing attackers to issue BIOS writes during the timing window [REF-1237].
https://www.cve.org/CVERecord?id=CVE-2014-8273

CVE-2008-5044
Race condition leading to a crash by calling a hook removal procedure while other activities are occurring at the same time.
https://www.cve.org/CVERecord?id=CVE-2008-5044

CVE-2008-2958
chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.
https://www.cve.org/CVERecord?id=CVE-2008-2958

CVE-2008-1570
chain: time-of-check time-of-use (TOCTOU) race condition in program allows bypass of protection mechanism that was designed to prevent symlink attacks.
https://www.cve.org/CVERecord?id=CVE-2008-1570

CVE-2008-0058
Unsynchronized caching operation enables a race condition that causes messages to be sent to a deallocated object.
https://www.cve.org/CVERecord?id=CVE-2008-0058

CVE-2008-0379
Race condition during initialization triggers a buffer overflow.
https://www.cve.org/CVERecord?id=CVE-2008-0379

CVE-2007-6599
Daemon crash by quickly performing operations and undoing them, which eventually leads to an operation that does not acquire a lock.
https://www.cve.org/CVERecord?id=CVE-2007-6599

CVE-2007-6180
chain: race condition triggers NULL pointer dereference
https://www.cve.org/CVERecord?id=CVE-2007-6180

CVE-2007-5794
Race condition in library function could cause data to be sent to the wrong process.
https://www.cve.org/CVERecord?id=CVE-2007-5794

CVE-2007-3970
Race condition in file parser leads to heap corruption.
https://www.cve.org/CVERecord?id=CVE-2007-3970

CVE-2008-5021
chain: race condition allows attacker to access an object while it is still being initialized, causing software to access uninitialized memory.
https://www.cve.org/CVERecord?id=CVE-2008-5021

CVE-2009-4895
chain: race condition for an argument value, possibly resulting in NULL dereference
https://www.cve.org/CVERecord?id=CVE-2009-4895

CVE-2009-3547
Chain: race condition (CWE-362) might allow resource to be released before operating on it, leading to NULL dereference (CWE-476)
https://www.cve.org/CVERecord?id=CVE-2009-3547

CVE-2006-5051
Chain: Signal handler contains too much functionality (CWE-828), introducing a race condition (CWE-362) that leads to a double free (CWE-415).
https://www.cve.org/CVERecord?id=CVE-2006-5051

File or Directory

Race Conditions

VNA03-J
Do not assume that a group of calls to independently atomic methods is atomic

Allowed-with-Review
This CWE entry is a Class and might have Base-level children that would be more appropriate
Examine children of this entry to see if there is a better fit

The relationship between race conditions and synchronization problems (CWE-662) needs to be further developed. They are not necessarily two perspectives of the same core concept, since synchronization is only one technique for avoiding race conditions, and synchronization can be used for other purposes besides race condition prevention.
Race conditions in web applications are under-studied and probably under-reported. However, in 2008 there has been growing interest in this area.
Much of the focus of race condition research has been in Time-of-check Time-of-use (TOCTOU) variants (CWE-367), but many race conditions are related to synchronization problems that do not necessarily require a time-of-check.
From a classification/taxonomy perspective, the relationships between concurrency and program state need closer investigation and may be useful in organizing related issues.

PLOVER
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2008-10-14
updated Relationships

CWE Content Team
MITRE
2008-11-24
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2009-01-12
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Likelihood_of_Exploit, Maintenance_Notes, Observed_Examples, Potential_Mitigations, References, Relationships, Research_Gaps

CWE Content Team
MITRE
2009-03-10
updated Demonstrative_Examples, Potential_Mitigations

CWE Content Team
MITRE
2009-05-27
updated Relationships

CWE Content Team
MITRE
2010-02-16
updated Detection_Factors, References, Relationships

CWE Content Team
MITRE
2010-06-21
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References

CWE Content Team
MITRE
2010-09-27
updated Observed_Examples, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2010-12-13
updated Applicable_Platforms, Demonstrative_Examples, Description, Name, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2011-06-27
updated Relationships

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Potential_Mitigations, References, Relationships

CWE Content Team
MITRE
2014-07-30
updated Detection_Factors, Relationships

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples, References, Research_Gaps, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-06-20
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Applicable_Platforms, Demonstrative_Examples, Observed_Examples, Relationships

CWE Content Team
MITRE
2020-08-20
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples

CWE Content Team
MITRE
2021-10-28
updated Observed_Examples, References

CWE Content Team
MITRE
2022-04-28
updated Observed_Examples, Relationships

CWE Content Team
MITRE
2022-06-28
updated Observed_Examples, Relationships

CWE Content Team
MITRE
2022-10-13
updated Observed_Examples, References

CWE Content Team
MITRE
2023-01-31
updated Applicable_Platforms, Common_Consequences, Description

CWE Content Team
MITRE
2023-04-27
updated References, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes, Relationships

CWE Content Team
MITRE
2024-07-16
4.15
2024-07-16
updated Relationships

CWE Content Team
MITRE
2024-11-19
4.16
2024-11-19
updated Alternate_Terms, Common_Consequences, Description, Diagram, Modes_of_Introduction

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Affected_Resources

CWE Content Team
MITRE
2025-09-09
4.18
2025-09-09
updated Detection_Factors, References

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Observed_Examples, Relationships, Weakness_Ordinalities

Martin Sebor
Cisco Systems, Inc.
2010-04-30
Provided Demonstrative Example

Abhi Balakrishnan
2024-02-29
4.16
2024-11-19
Provided diagram to improve CWE usability

Race Conditions
Race Condition