CWE-783 操作符优先级逻辑错误

Operator Precedence Logic Error

结构: Simple

Abstraction: Base

状态: Draft

被利用可能性: Low


The program uses an expression in which operator precedence causes incorrect logic to be used.


While often just a bug, operator precedence logic errors can have serious consequences if they are used in security-critical code, such as making an authentication decision.


  • cwe_Nature: ChildOf cwe_CWE_ID: 670 cwe_View_ID: 1000 cwe_Ordinal: Primary


Language: [{'cwe_Name': 'C', 'cwe_Prevalence': 'Rarely'}, {'cwe_Name': 'C++', 'cwe_Prevalence': 'Rarely'}, {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Rarely'}]


范围 影响 注释
['Confidentiality', 'Integrity', 'Availability'] ['Varies by Context', 'Unexpected State'] The consequences will vary based on the context surrounding the incorrect precedence. In a security decision, integrity or confidentiality are the most likely results. Otherwise, a crash may occur due to the software reaching an unexpected state.




Regularly wrap sub-expressions in parentheses, especially in security-critical code.


In the following example, the method validateUser makes a call to another method to authenticate a username and password for a user and returns a success or failure code.

bad C

#define FAIL 0
#define SUCCESS 1


int validateUser(char username, char password) {

int isUser = FAIL;

// call method to authenticate username and password

// if authentication fails then return failure otherwise return success
if (isUser = AuthenticateUser(username, password) == FAIL) {
return isUser;
else {
isUser = SUCCESS;

return isUser;

However, the method that authenticates the username and password is called within an if statement with incorrect operator precedence logic. Because the comparison operator "==" has a higher precedence than the assignment operator "=", the comparison operator will be evaluated first and if the method returns FAIL then the comparison will be true, the return variable will be set to true and SUCCESS will be returned. This operator precedence logic error can be easily resolved by properly using parentheses within the expression of the if statement, as shown below.

good C


if ((isUser = AuthenticateUser(username, password)) == FAIL) {


In this example, the method calculates the return on investment for an accounting/financial application. The return on investment is calculated by subtracting the initial investment costs from the current value and then dividing by the initial investment costs.

bad Java

public double calculateReturnOnInvestment(double currentValue, double initialInvestment) {

double returnROI = 0.0;

// calculate return on investment
returnROI = currentValue - initialInvestment / initialInvestment;

return returnROI;

However, the return on investment calculation will not produce correct results because of the incorrect operator precedence logic in the equation. The divide operator has a higher precedence than the minus operator, therefore the equation will divide the initial investment costs by the initial investment costs which will only subtract one from the current value. Again this operator precedence logic error can be resolved by the correct use of parentheses within the equation, as shown below.

good Java


returnROI = (currentValue - initialInvestment) / initialInvestment;


Note that the initialInvestment variable in this example should be validated to ensure that it is greater than zero to avoid a potential divide by zero error (CWE-369).


标识 说明 链接
CVE-2008-2516 Authentication module allows authentication bypass because it uses "(x = call(args) == SUCCESS)" instead of "((x = call(args)) == SUCCESS)".
CVE-2008-0599 Chain: Language interpreter calculates wrong buffer size (CWE-131) by using "size = ptr ? X : Y" instead of "size = (ptr ? X : Y)" expression.
CVE-2001-1155 Chain: product does not properly check the result of a reverse DNS lookup because of operator precedence (CWE-783), allowing bypass of DNS-based access restrictions.


映射的分类名 ImNode ID Fit Mapped Node Name
CERT C Secure Coding EXP00-C Exact Use parentheses for precedence of operation
SEI CERT Perl Coding Standard EXP04-PL CWE More Abstract Do not mix the early-precedence logical operators with late-precedence logical operators