Variant weakness

Draft

CWE-481: Assigning instead of Comparing

The code uses an operator for assignment when the intention was to perform a comparison.

Recorded CVEs

With this primary weakness

KEVs

In the CISA KEV catalog

Low

Likelihood of exploit

Per MITRE

Variant

Abstraction

MITRE classification

Overview

In many languages the compare statement is very close in appearance to the assignment statement and are often confused. This bug is generally the result of a typo and usually causes obvious problems with program execution. If the comparison is in an if statement, the if statement will usually evaluate the value of the right-hand side of the predicate.

Code examples

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

The following C/C++ and C# examples attempt to validate an int input parameter against the integer value 100.

Vulnerable example

int isValid(int value) {

Vulnerable example

csharp

bool isValid(int value) {

However, the expression to be evaluated in the if statement uses the assignment operator "=" rather than the comparison operator "==". The result of using the assignment operator instead of the comparison operator causes the int variable to be reassigned locally and the expression in the if statement will always evaluate to the value on the right hand side of the expression. This will result in the input value not being properly validated, which can cause unexpected results.

In this example, we show how assigning instead of comparing can impact code when values are being passed by reference instead of by value. Consider a scenario in which a string is being processed from user input. Assume the string has already been formatted such that different user inputs are concatenated with the colon character. When the processString function is called, the test for the colon character will result in an insertion of the colon character instead, adding new input separators. Since the string was passed by reference, the data sentinels will be inserted in the original string (CWE-464), and further processing of the inputs will be altered, possibly malformed.

Vulnerable example

void processString (char *str) {

The following Java example attempts to perform some processing based on the boolean value of the input parameter. However, the expression to be evaluated in the if statement uses the assignment operator "=" rather than the comparison operator "==". As with the previous examples, the variable will be reassigned locally and the expression in the if statement will evaluate to true and unintended processing may occur.

Vulnerable example

java

public void checkValid(boolean isValid) {

Safe example

java

public void checkValid(boolean isValid) {

Safe example

java

public void checkValid(boolean isValid) {

The following example demonstrates the weakness.

Vulnerable example

void called(int foo){

CWE-481: Assigning instead of Comparing

Overview

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Automated Static Analysis - Source Code

Code examples

Terminology & mappings

Mapped taxonomies

Frequently asked questions

What is CWE-481?

How do you prevent CWE-481?

How is CWE-481 detected?

What are the consequences of CWE-481?

References

Stay ahead of CWE-481

Overview

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Automated Static Analysis - Source Code

Code examples

Related weaknesses

Parent

Can precede

Terminology & mappings

Mapped taxonomies

Frequently asked questions

What is CWE-481?

How do you prevent CWE-481?

How is CWE-481 detected?

What are the consequences of CWE-481?

References

Stay ahead of CWE-481