CWE-362 使用共享资源的并发执行不恰当同步问题(竞争条件)

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

结构: Simple

Abstraction: Class

状态: Draft

被利用可能性: Medium


The program contains a code sequence that can run concurrently with other code, and the code sequence 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 that is operating concurrently.


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.

A race condition occurs within concurrent environments, and 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:

A race condition exists when an "interfering code sequence" can still access the shared resource, violating exclusivity. 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).

The interfering code sequence could be "trusted" or "untrusted." A trusted interfering code sequence occurs within the program; 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 program.


  • cwe_Nature: ChildOf cwe_CWE_ID: 691 cwe_View_ID: 1000 cwe_Ordinal: Primary


Language: [{'cwe_Name': 'C', 'cwe_Prevalence': 'Sometimes'}, {'cwe_Name': 'C++', 'cwe_Prevalence': 'Sometimes'}, {'cwe_Name': 'Java', 'cwe_Prevalence': 'Sometimes'}, {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Undetermined'}]

Paradigm: {'cwe_Name': 'Concurrent Systems Operating on Shared Resources', 'cwe_Prevalence': 'Often'}


范围 影响 注释
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 (CWE-400).
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 program(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).


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).

DM-2 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.

Automated Static Analysis - Binary or Bytecode

According to SOAR, 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

Dynamic Analysis with Automated Results Interpretation

According to SOAR, the following detection techniques may be useful:

Cost effective for partial coverage:
  • Web Application Scanner
  • Web Services Scanner
  • Database Scanners

Dynamic Analysis with Manual Results Interpretation

According to SOAR, 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

Manual Static Analysis - Source Code

According to SOAR, 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

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Highly cost effective:
  • Source code Weakness Analyzer
  • Context-configured Source Code Weakness Analyzer

Architecture or Design Review

According to SOAR, 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.)


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).



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



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.



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



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



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.



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.

MIT-17 ['Architecture and Design', 'Operation']

策略: 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.

bad Perl

$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");
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:

attack Other

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 100.00
PROGRAM-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.

bad C

void f(pthread_mutex_t mutex) {

access shared resource */


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 it 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);


标识 说明 链接
CVE-2008-5044 Race condition leading to a crash by calling a hook removal procedure while other activities are occurring at the same time.
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.
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.
CVE-2008-0058 Unsynchronized caching operation enables a race condition that causes messages to be sent to a deallocated object.
CVE-2008-0379 Race condition during initialization triggers a buffer overflow.
CVE-2007-6599 Daemon crash by quickly performing operations and undoing them, which eventually leads to an operation that does not acquire a lock.
CVE-2007-6180 chain: race condition triggers NULL pointer dereference
CVE-2007-5794 Race condition in library function could cause data to be sent to the wrong process.
CVE-2007-3970 Race condition in file parser leads to heap corruption.
CVE-2008-5021 chain: race condition allows attacker to access an object while it is still being initialized, causing software to access uninitialized memory.
CVE-2009-4895 chain: race condition for an argument value, possibly resulting in NULL dereference
CVE-2009-3547 chain: race condition might allow resource to be released before operating on it, leading to NULL dereference


Maintenance 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. Research Gap Race conditions in web applications are under-studied and probably under-reported. However, in 2008 there has been growing interest in this area. Research Gap 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. Research Gap From a classification/taxonomy perspective, the relationships between concurrency and program state need closer investigation and may be useful in organizing related issues.


映射的分类名 ImNode ID Fit Mapped Node Name
PLOVER Race Conditions
The CERT Oracle Secure Coding Standard for Java (2011) VNA03-J Do not assume that a group of calls to independently atomic methods is atomic


  • CAPEC-26
  • CAPEC-29