Critical Variable Declared Public
Weakness ID: 766 (Weakness Variant)Status: Incomplete
+ Description

Description Summary

The software declares a critical variable or field to be public when intended security policy requires it to be private.
+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

C++

C#

Java

+ Common Consequences
ScopeEffect
Integrity
Confidentiality

Making a critical variable public allows anyone with access to the object in which the variable is contained to alter or read the value.

+ Likelihood of Exploit

Low to Medium

+ Demonstrative Examples

Example 1

The following example declares a critical variable public, making it accessible to anyone with access to the object in which it is contained.

(Bad Code)
Example Language: C++ 
public: char* password;

Instead, the critical data should be declared private.

(Good Code)
Example Language: C++ 
private: char* password;

Even though this example declares the password to be private, there are other possible issues with this implementation, such as the possibility of recovering the password from process memory (CWE-257).

Example 2

The following example shows a basic user account class that includes member variables for the username and password as well as a public constructor for the class and a public method to authorize access to the user account.

(Bad Code)
Example Language: C++ 
#define MAX_PASSWORD_LENGTH 15
#define MAX_USERNAME_LENGTH 15

class UserAccount
{
public:
UserAccount(char *username, char *password)
{
if ((strlen(username) > MAX_USERNAME_LENGTH) ||
(strlen(password) > MAX_PASSWORD_LENGTH)) {
ExitError("Invalid username or password");
}
strcpy(this->username, username);
strcpy(this->password, password);
}

int authorizeAccess(char *username, char *password)
{
if ((strlen(username) > MAX_USERNAME_LENGTH) ||
(strlen(password) > MAX_PASSWORD_LENGTH)) {
ExitError("Invalid username or password");
}
// if the username and password in the input parameters are equal to
// the username and password of this account class then authorize access
if (strcmp(this->username, username) ||
strcmp(this->password, password))
return 0;
// otherwise do not authorize access
else
return 1;
}

char username[MAX_USERNAME_LENGTH+1];
char password[MAX_PASSWORD_LENGTH+1];
};

However, the member variables username and password are declared public and therefore will allow access and changes to the member variables to anyone with access to the object. These member variables should be declared private as shown below to prevent unauthorized access and changes.

(Good Code)
Example Language: C++ 
class UserAccount
{
public:
...

private:
char username[MAX_USERNAME_LENGTH+1];
char password[MAX_PASSWORD_LENGTH+1];
};
+ Potential Mitigations

Phase: Implementation

Data should be private, static, and final whenever possible. This will assure that your code is protected by instantiating early, preventing access, and preventing tampering.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class485Insufficient Encapsulation
Development Concepts (primary)699
Research Concepts1000
ChildOfWeakness ClassWeakness Class668Exposure of Resource to Wrong Sphere
Research Concepts (primary)1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPFailure to protect stored data from modification
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
2009-03-03Internal CWE Team
Modifications
Modification DateModifierOrganizationSource
2009-12-28CWE Content TeamMITREInternal
updated Demonstrative Examples
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