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Callers can trivially access and modify public non-final nonfinal static fields. Neither accesses nor modifications can be checked by a SecurityManager, and newly set values can not cannot be validated. Furthermore, multiple threads can modify non-final nonfinal public static data in ways that are not consistent.

Noncompliant

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Code Example

Wiki Markup
This is an example from the JDK 1.4.2 software. \[[Function Table|#ref3]\].

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package org.apache.xpath.compiler;

public class FunctionTable {
    public static FuncLoader m_functions;
}

An attacker can replace the function table as follows:

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FunctionTable.m_functions = <new_table>;

Replacing the function table gives the attacker access to the XPathContext used to evaluate XPath expressions. The XPathContext is used to set the reference node for evaluating XPath expressions. Manipulating this can cause unexpected behavior, and XML fields can be modified in inconsistent ways. Also, static variables are global across a Java runtime environment. They can be used as a communication channel between different application domains (e.g., by code loaded into different class loaders).

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Compliant Solution

Additionally, for mutable static state one can define assessor methods and add appropriate security checks. Note that this is a different example and in this case the scope of the static variable has been changed to private.

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public class MyClass {

    private static byte[] data;
    public static byte[] getData() {
        return data.clone();
    }

    public static void setData(byte[] b) {
        securityCheck();
       data = b.clone();
    }
}

However as As a cautionary note however, simply changing the modifier to final may not prevent attackers from indirectly indirectly retrieving an incorrect value from the static final variable before its initialization. See Eliminate Class Initialization Cycles for more on this problem.

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