CWE-362: Race Condition

How it's found

Race Condition describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.

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: 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.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.

Vulnerable vs. safe

/* access shared resource */pthread_mutex_lock(mutex);pthread_mutex_unlock(mutex);void f(pthread_mutex_t *mutex) {}

return result;/* access shared resource */int result;result = pthread_mutex_lock(mutex);if (0 != result)return pthread_mutex_unlock(mutex);int f(pthread_mutex_t *mutex) {}

Consequences

• 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.
• 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.
• 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).
• 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.

Mitigations

• 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: 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.

Where this fits in a TurboPentest engagement

This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.

Frequently asked questions

Related CWEs

• Class weakness
  CWE-662: Improper Synchronization