Use of Blocking Code in Single-threaded, Non-blocking Context

The product uses a non-blocking model that relies on a single threaded process for features such as scalability, but it contains code that can block when it is invoked.


When an attacker can directly invoke the blocking code, or the blocking code can be affected by environmental conditions that can be influenced by an attacker, then this can lead to a denial of service by causing unexpected hang or freeze of the code. Examples of blocking code might be an expensive computation or calling blocking library calls, such as those that perform exclusive file operations or require a successful network operation.

Due to limitations in multi-thread models, single-threaded models are used to overcome the resource constraints that are caused by using many threads. In such a model, all code should generally be non-blocking. If blocking code is called, then the event loop will effectively be stopped, which can be undesirable or dangerous. Such models are used in Python asyncio, Vert.x, and Node.js, or other custom event loop code.

See Also

Comprehensive Categorization: Insufficient Control Flow Management

Weaknesses in this category are related to insufficient control flow management.

Concurrency Issues

Weaknesses in this category are related to concurrent use of shared resources.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

Weakness Base Elements

This view (slice) displays only weakness base elements.

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