Improper Handling of Faults that Lead to Instruction Skips

The device is missing or incorrectly implements circuitry or sensors that detect and mitigate the skipping of security-critical CPU instructions when they occur.


The operating conditions of hardware may change in ways that cause unexpected behavior to occur, including the skipping of security-critical CPU instructions. Generally, this can occur due to electrical disturbances or when the device operates outside of its expected conditions.

In practice, application code may contain conditional branches that are security-sensitive (e.g., accepting or rejecting a user-provided password). These conditional branches are typically implemented by a single conditional branch instruction in the program binary which, if skipped, may lead to effectively flipping the branch condition - i.e., causing the wrong security-sensitive branch to be taken. This affects processes such as firmware authentication, password verification, and other security-sensitive decision points.

Attackers can use fault injection techniques to alter the operating conditions of hardware so that security-critical instructions are skipped more frequently or more reliably than they would in a "natural" setting.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

A smart card contains authentication credentials that are used as authorization to enter a building. The credentials are only accessible when a correct PIN is presented to the card.

The card emits the credentials when a voltage anomaly is injected into the power line to the device at a particular time after providing an incorrect PIN to the card, causing the internal program to accept the incorrect PIN.

There are several ways this weakness could be fixed.

add an internal filter or internal power supply in series with the power supply pin on the deviceadd sensing circuitry to reset the device if out of tolerance conditions are detectedadd additional execution sensing circuits to monitor the execution order for anomalies and abort the action or reset the device under fault conditions

See Also

Comprehensive Categorization: Improper Check or Handling of Exceptional Conditions

Weaknesses in this category are related to improper check or handling of exceptional conditions.

Physical Access Issues and Concerns

Weaknesses in this category are related to concerns of physical access.

ICS Communications: Unreliability

Weaknesses in this category are related to the "Unreliability" category from the SEI ETF "Categories of Security Vulnerabilities in ICS" as published in March 2022: "V...

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.

Weaknesses Introduced During Design

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

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