CWE-481: Assigning instead of Comparing
The code uses an operator for assignment when the intention was to perform a comparison.
View on MITREExtended Description
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.
Technical Details
- Structure
- Simple
Applicable To
Security Consequences
Scope
Impact
Mitigation Strategies
Phase
Description
Many IDEs and static analysis products will detect this problem.
Phase
Description
Place constants on the left. If one attempts to assign a constant with a variable, the compiler will produce an error.
Detection Methods
No detection method information available for this CWE.
Code Examples & CVEs
Demonstrative Examples
The following C/C++ and C# examples attempt to validate an int input parameter against the integer value 100.
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.
The following C/C++ and C# examples attempt to validate an int input parameter against the integer value 100.
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..
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.
While most Java compilers will catch the use of an assignment operator when a comparison operator is required, for boolean variables in Java the use of the assignment operator within an expression is allowed. If possible, try to avoid using comparison operators on boolean variables in java. Instead, let the values of the variables stand for themselves, as in the following code.
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.
While most Java compilers will catch the use of an assignment operator when a comparison operator is required, for boolean variables in Java the use of the assignment operator within an expression is allowed. If possible, try to avoid using comparison operators on boolean variables in java. Instead, let the values of the variables stand for themselves, as in the following code.
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.
While most Java compilers will catch the use of an assignment operator when a comparison operator is required, for boolean variables in Java the use of the assignment operator within an expression is allowed. If possible, try to avoid using comparison operators on boolean variables in java. Instead, let the values of the variables stand for themselves, as in the following code.
The following example demonstrates the weakness.
CWE Relationships
Frequently Asked Questions
What is CWE-481: Assigning instead of Comparing?+
CWE-481: Assigning instead of Comparing is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The code uses an operator for assignment when the intention was to perform a comparison. 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.
What are the security consequences of Assigning instead of Comparing?+
If exploited, CWE-481 (Assigning instead of Comparing) it can compromise Other, leading to outcomes such as Alter Execution Logic.
How do you prevent or mitigate Assigning instead of Comparing?+
Recommended mitigations for CWE-481 include: Many IDEs and static analysis products will detect this problem. Place constants on the left. If one attempts to assign a constant with a variable, the compiler will produce an error.
Which programming languages are affected by Assigning instead of Comparing?+
CWE-481 commonly affects C, C++, Java and C#. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
What is the difference between a CWE and a CVE?+
A CWE (Common Weakness Enumeration) like CWE-481 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.