Common Weakness Enumeration

A Community-Developed List of Software & Hardware Weakness Types

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CWE-1322: Use of Blocking Code in Single-threaded, Non-blocking Context

Weakness ID: 1322
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
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.
+ Extended Description

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.

+ Relationships

The table(s) below 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" (CWE-1000)
ChildOfClassClass - 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.834Excessive Iteration
CanPrecedeBaseBase - 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.835Loop with Unreachable Exit Condition ('Infinite Loop')
+ Modes Of Introduction

The 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.

+ Common Consequences

The table below 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.


Technical Impact: DoS: Resource Consumption (CPU)

An unexpected call to blocking code can trigger an infinite loop, or a large loop that causes the software to pause and wait indefinitely.
+ Potential Mitigations

Phase: Implementation

Generally speaking, blocking calls should be replaced with non-blocking alternatives that can be used asynchronously. Expensive computations should be passed off to worker threads, although the correct approach depends on the framework being used.

Phase: Implementation

For expensive computations, consider breaking them up into multiple smaller computations. Refer to the documentation of the framework being used for guidance.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2019-10-25Joe Harvey
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Page Last Updated: December 10, 2020