The code does not have a default case in an expression with multiple conditions, such as a switch statement.

What CVEs are caused by CWE-478?

1 recorded CVEs are attributed to CWE-478, including CVE-2026-33064.

How do you prevent CWE-478?

Ensure that there are no cases unaccounted for when adjusting program flow or values based on the value of a given variable. In the case of switch style statements, the very simple act of creating a default case can, if done correctly, mitigate this situation. Often however, the default case is used simply to represent an assumed option, as opposed to working as a check for invalid input. This is poor practice and in some cases is as bad as omitting a default case entirely.

How is CWE-478 detected?

Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

What are the consequences of CWE-478?

Exploiting CWE-478 can lead to: Varies by Context, Alter Execution Logic.

Is CWE-478 actively exploited?

1 recorded CVEs are caused by CWE-478; none are currently in CISA's KEV catalog of actively exploited flaws.

CWE-478: Missing Default Case in Multiple Condition Expression

Code examples

Illustrative examples from MITRE showing how the weakness appears in code.

The following does not properly check the return code in the case where the security_check function returns a -1 value when an error occurs. If an attacker can supply data that will invoke an error, the attacker can bypass the security check:

Vulnerable example

// program execution continues...
#define FAILED 0

Safe example

#define FAILED 0

In the following Java example the method getInterestRate retrieves the interest rate for the number of points for a mortgage. The number of points is provided within the input parameter and a switch statement will set the interest rate value to be returned based on the number of points.

Vulnerable example

java

public static final String INTEREST_RATE_AT_ZERO_POINTS = "5.00";

Safe example

java

public static final String INTEREST_RATE_AT_ZERO_POINTS = "5.00";

However, this code assumes that the value of the points input parameter will always be 0, 1 or 2 and does not check for other incorrect values passed to the method. This can be easily accomplished by providing a default label in the switch statement that outputs an error message indicating an invalid value for the points input parameter and returning a null value.

In the following Python example the match-case statements (available in Python version 3.10 and later) perform actions based on the result of the process_data() function. The expected return is either 0 or 1. However, if an unexpected result (e.g., -1 or 2) is obtained then no actions will be taken potentially leading to an unexpected program state.

Vulnerable example

python

result = process_data(data)

Safe example

python

result = process_data(data)

The recommended approach is to add a default case that captures any unexpected result conditions, regardless of how improbable these unexpected conditions might be, and properly handles them.

In the following JavaScript example the switch-case statements (available in JavaScript version 1.2 and later) are used to process a given step based on the result of a calcuation involving two inputs. The expected return is either 1, 2, or 3. However, if an unexpected result (e.g., 4) is obtained then no action will be taken potentially leading to an unexpected program state.

Vulnerable example

javascript

let step = input1 + input2;

Safe example

javascript

let step = input1 + input2;

The recommended approach is to add a default case that captures any unexpected result conditions and properly handles them.

The Finite State Machine (FSM) shown in the "bad" code snippet below assigns the output ("out") based on the value of state, which is determined based on the user provided input ("user_input").

Vulnerable example

verilog

module fsm_1(out, user_input, clk, rst_n);

Safe example

verilog

case (user_input)

The case statement does not include a default to handle the scenario when the user provides inputs of 3'h6 and 3'h7. Those inputs push the system to an undefined state and might cause a crash (denial of service) or any other unanticipated outcome.

Adding a default statement to handle undefined inputs mitigates this issue. This is shown in the "Good" code snippet below. The default statement is in bold.

CWE-478: Missing Default Case in Multiple Condition Expression

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Code examples

Terminology & mappings

Mapped taxonomies

Frequently asked questions

References

Stay ahead of CWE-478

Overview

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Code examples

Related weaknesses

Parent

Terminology & mappings

Mapped taxonomies

Frequently asked questions

References

Stay ahead of CWE-478