Unsafe Mobile Code

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ASDR Table of Contents

Last revision (mm/dd/yy): 02/17/2009

Description

Mobile code, such as a Java Applet, is code that is transmitted across a network and executed on a remote machine. Because mobile code developers have little if any control of the environment in which their code will execute, special security concerns become relevant. One of the biggest environmental threats results from the risk that the mobile code will run side-by-side with other, potentially malicious, mobile code. Because all of the popular web browsers execute code from multiple sources together in the same JVM, many of the security guidelines for mobile code are focused on preventing manipulation of your objects' state and behavior by adversaries who have access to the same virtual machine where your program is running.

Access Violation

The program violates secure coding principles for mobile code by returning a private array variable from a public access method.

Returning a private array variable from a public access method allows the calling code to modify the contents of the array, effectively giving the array public access and contradicting the intentions of the programmer who made it private.

Example

The following Java Applet code mistakenly returns a private array variable from a public access method.

	public final class urlTool extends Applet {
		private URL[] urls;
		public URL[] getURLs() {
			return urls;
		}
			...
	}

.

Dangerous Array Declaration

The program violates secure coding principles for mobile code by declaring an array public, final and static.

In most cases an array declared public, final and static is a bug. Because arrays are mutable objects, the final constraint requires that the array object itself be assigned only once, but makes no guarantees about the values of the array elements. Since the array is public, a malicious program can change the values stored in the array. In most situations the array should be made private.

Example

The following Java Applet code mistakenly declares an array public, final and static.

	public final class urlTool extends Applet {
		public final static URL[] urls;
		...
	}

Dangerous Public Field

The program violates secure coding principles for mobile code by declaring a member variable public but not final.

All public member variables in an Applet and in classes used by an Applet should be declared final to prevent an attacker from manipulating or gaining unauthorized access to the internal state of the Applet.

Example

The following Java Applet code mistakenly declares a member variable public but not final.

	public final class urlTool extends Applet {
		public URL url;
		...
	}

Risk Factors

• Talk about the factors that make this vulnerability likely or unlikely to actually happen
• Discuss the technical impact of a successful exploit of this vulnerability
• Consider the likely [business impacts] of a successful attack

Related Attacks

• Attack 1
• Attack 2

Related Vulnerabilities

• Vulnerability 1
• Vulnerabiltiy 2

Related Controls

• Use encapsulation

Related Technical Impacts

• Technical Impact 1
• Technical Impact 2

References

TBD