Mixing Signed Code Ensuring Application Security

Mixing Signed and Unsigned Code Ensuring Application and Applet Security

docs.oracle.com

Contents

Overview

Signed Java Web Start applications and applets that contain signed and unsigned components could potentially be unsafe unless the mixed code was intended by the application vendor. As of the Java SE 6 Update 19 release (or later), when a program contains both signed and unsigned components, a warning dialog is raised. The following is an example of the dialog that the user may see:

Clicking the More Information... link brings up the following panel:

Clicking Yes blocks potentially unsafe components from running, and the program may terminate. If the user clicks the No button, the application or applet continues execution with some added protections.

Raising a warning is the default behavior, but there are options available to manage how this situation is handled.

---

Note: If any concepts are unclear, such as how to modify a manifest file, or how to sign a jar file, or how to use a deployment configuration file, see For More Information for useful links.

---

Mixed Code Protection Options for Users

There are two mechanisms for managing how mixed code programs are handled.

• From the Java Control Panel

  You can manage how mixed code programs are handled via the Java Control Panel. The following screen shot shows the four levels of control available. See the Mixed code heading towards the bottom of the panel.

  

  How to access the Java Control Panel varies for each platform and sometimes varies for different releases of a platform. On Microsoft Windows Vista and XP, you can bring up the panel via Start menu > Control Panel > Java Control Panel.

  The first three options enable the software protections, but behave a bit differently.

  • Enable - show warning if needed
    This is the default setting. When a potential security risk is encountered, a warning dialog is raised. Clicking Yes blocks potentially unsafe components from running and may terminate the program. When the user clicks No, the application or applet continues execution with some added protections (packages or resources that are later encountered with the same names but have different trust levels, i.e., sign vs unsigned, will not be loaded).
  • Enable - hide warning and run with protections
    This option suppresses the warning dialog. The code executes as if the user had clicked No from the warning dialog.
  • Enable - hide warning and don't run untrusted code
    This option suppresses the warning dialog and behaves as if the user had clicked Yes from the warning dialog.

  The final option, Disable verification, is not recommended. This option completely disables the software from checking for mixing trusted and untrusted code, leaving the user to run potentially unsafe code with no warning and without the additional protections.

• From the deployment.properties File

  The mixed code protection options can also be set by using the deployment.security.mixcode deployment property, as described in Deployment Configuration File and Properties.

  • deployment.security.mixcode=ENABLE

    This option enables mixed code verification. When a potential security risk is encountered, a warning dialog is raised. This is the default value for this property.

  • deployment.security.mixcode=HIDE_RUN

    This option suppresses the warning dialog. The code executes as if the user had clicked No from the warning dialog.

  • deployment.security.mixcode=HIDE_CANCEL

    This option suppresses the warning dialog and behaves as if the user had clicked Yes from the warning dialog.

  • deployment.security.mixcode=DISABLE

    This option is not recommended. The software is disabled from checking for mixing trusted and untrusted code, leaving the user to run potentially unsafe code with no warning and without the additional protections.

---

Version note: To take advantage of these security enhancements, users need to install the Java SE or Java for Business 6 Update 19 release (or later) and use the new Java Plugin, which is enabled by default. To use an earlier JRE with the new Java Plugin, you need to install the Java for Business 5.0 Update 24 release (or later) or the Java for Business 1.4.2_26 release (or later) in order to enable the mixed code security enhancement for those release families.
Note 1: Mixed code checking for the 1.4.2 release is available only for the Windows platform.
Note 2: For Solaris, the new Java Plugin requires Firefox 3 or later. Netscape 7 and Firefox 2 are not supported.
Note 3: For more information on which platforms are supported by the new plugin, see the Release Notes for the Next-Generation Java Plugin.

---

Deploying Signed Applications and Applets Securely Without a Mixed Code Warning

This section describes best practices for developers and deployers to protect their applications and applets from being maliciously re-purposed by replacing trusted components with untrusted ones.

Two new JAR manifest attributes are available, as of Java SE 6 Update 19, for deploying signed applications and applets. A warning dialog is not displayed when one of these manifest attributes is included.

Developers and deployers should check their signed Java Web Start applications and applets to determine if they mix signed and unsigned code. If users of these applications and applets may inadvertently download these applications and applets from rogue websites, deploying or re-deploying with one of the following attributes should be considered. Existing signed jars need to be re-signed after adding one of these manifest attributes. Note: source code of the classes and resources are not required for re-signing with the new manifest entries.

Trusted-Only Attribute

For applications and applets that do not require unsigned components, the Trusted-Only attribute should be used. No warning dialog will be displayed and an application or applet that loads a jar file containing this attribute will not load any untrusted classes or resources. This attribute prevents a signed application or applet from being re-purposed with unsigned components. You can specify Trusted-Only: true in the manifest file. For example:

Manifest-Version: 1.0 Trusted-Only: true Created-By: 1.6.0-internal (Sun Microsystems Inc.)

All classes and resources in the application or applet must be signed and trusted.

Trusted-Library Attribute

For applications and applets that are designed to allow unsigned components, the Trusted-Library attribute should be used. No warning dialog will be displayed and an application or applet may load jar files containing untrusted classes or resources. This attribute prevents signed components in an application or applet from being re-purposed with unsigned components. You can specify Trusted-Library: true in the manifest file. For example:

Manifest-Version: 1.0 Trusted-Library: true Created-By: 1.6.0-internal (Sun Microsystems Inc.)

All classes and resources in a jar file containing this manifest attribute must be signed and trusted.

In a mixed code application or applet, all signed classes and resources must be included in jar files that contain the Trusted-Library attribute.

All trusted library jars are loaded into a separate dedicated class loader which is unique to the application or applet instance. This new Trusted-Library loader is now the parent of the normal Web Start or applet class loader. For backwards compatibility with the original search order, both loaders cooperate to implement a common class path. Consistent with prior releases, jar files are lazily downloaded and opened as needed to find requested classes and resources.

Code in a jar file that is to be marked with the Trusted-Library manifest attribute may need to be modified slightly if it uses calls that are class loader dependent, such as the single parameter version of Class.forName(), Class.getResource(), and Class.getResourceAsStream(), some variants of java.util.ResourceBundle.getBundle(), and any other methods which operate relative to their immediate caller's defining loader. Changes only need to be made if the requested class or resource might be found in a jar file which is not a Trusted-Library (and is therefore loaded by the normal Web Start or applet class loader).

Code in a Trusted-Library can look up the normal loader by invoking Thread.currentThread().getContextClassLoader(). Note, however, that there are uncommon circumstances in which getContextClassLoader() may return null. For example, this may happen when the garbage collector uses a JRE system thread to invoke the Object.finalize() method of an unreachable instance.

If you need to convert class to Class.getResource() or Class.getResourceAsStream() to their ClassLoader equivalents, remember to adjust the string parameter as described by the documentation for those two methods. If the original resource name began with '/', then it was an absolute name and the leading '/' simply needs to be removed. Otherwise, determine if the class instance which was the target of the getResource call is in a named package. If it is an array you should first determine the underlying component type of the array. Invoke Class.getName() on the class or component type instance. If the class name contains any '.' characters, it is in a named package that will need to be prepended to the original resource name. Determine the package name by removing any characters after, and including, the trailing '.' character. Next, replace any remaining '.' characters with '/' characters. Finally, add a trailing '/' and append the original resource name string. This new string can now be passed to the ClassLoader version of the getResource() or getResourceAsStream() methods.

Generally, care must be taken to ensure that the code in the trusted library is written in a careful and secure manner and is otherwise compatible with being loaded in a separate class loader instance from any remaining jars which are part of the application and are loaded by the normal loader.

Mixed Code FAQ

• Question: I develop and/or deploy applications. How do I know whether I need to be concerned about this issue?

  Answer: If you do not use the new manifest entries and you encounter the warning dialog when running your signed application or applet, your program contains mixed code and is affected.

• Question: Is there a test I can run to determine whether I am affected?

  Answer: Test your Java Web Start applications and Java applets against Java SE or Java for Business 6 Update 19 or later. If you are running earlier release families, you should additionally install and test your program under 5.0 Update 24 (or later), or 1.4.2_26 (or later), as appropriate. If you see the warning dialog, then the Java Web Start application or applet contains mixed code.

• Question: What actions can I take?

  Answer: End users can click the "More Information" link before deciding whether to click "Yes" or "No" in response to the warning dialog. IT or System Administrators can choose from one of the Mixed Code protection options and configure enterprise desktops through the respective deployment properties described above. Developers and deployers can use the new manifest entries to protect their applications from tampering. No warning dialog will be displayed when one of these manifest entries is used.

• Question: What should Java ISVs, OEMs, and application vendors do with their code?

  Answer: Two manifest entries are available to application vendors to deploy, or re-deploy, their Java Web Start applications and Java applets.

• Question:What versions of Java SE and Java for Business are affected?

  Answer: The following releases from Oracle are affected:

  • Java SE and Java for Business 6 Update 18 and earlier
  • Java for Business 5.0 Update 23 and earlier
  • Java for Business 1.4.2_25 and earlier
• Question: What about Java applets and Java Web Start applications from the Internet, do I need to be concerned about those?

  Answer: Users will see a warning dialog if a signed Java Web Start application or Java applet contains mixed code regardless of whether it is downloaded from the Internet or Intranet.

• Question: What if I am behind a corporate firewall?

  Answer: The mixed code issue applies. See the question on applets and applications from the Internet.

• Question: Is this an issue for Oracle JRockit?

  Answer: No.

• Question: I am using an implementation of Java from another vendor. Are they affected in the same way?

  Answer: Please contact your vendor for advice on their implementation.

• Question: What are the risks to remaining on Java SE 6u18 (or earlier) to avoid seeing the warnings?

  Answer: Java SE 6 Update 19 (or later) contains the latest security fixes and Oracle recommends that customers use the latest release.

• Question: If I move to 6 Update 19 or later, what type of testing do I need to consider?

  Answer: See the question on testing. In addition, the release notes for each update release documents the latest changes included.

• Question: I am running on Solaris and/or Linux and I use Java applets. How do I leverage these security features?

  Answer: You need to use Firefox 3 and the next-generation Java Plugin. You can get Firefox 3 through sunfreeware.com. They have a full list of Firefox packages available. See Manual Installation and Registration of Solaris Plugin or Manual Installation and Registration of Linux Plugin, as appropriate, for more information.

• Question: I am a developer. What are the new security exceptions that are added with this enhancement?

  Answer: The following SecurityException messages are described for informational and debugging purposes only. The actual message contents may change between different implementations and releases.

  These SecurityExceptions are thrown when a jar file contains one of the new manifest attributes and the jar file itself contains untrusted components.

  attempted to open sandboxed jar "+ url +" as Trusted-Only attempted to open sandboxed jar "+ url +" as Trusted-Library

  The following SecurityException is thrown when a jar file contains the new Trusted-Only manifest attribute and untrusted components have previously been accessed.

  attempted to open Trusted-Only jar "+ url +" on sandboxed loader

  The following SecurityException is thrown when at least one jar containing the Trusted-Only manifest attribute has been opened and a subsequent attempt is made to load an untrusted component.

  Trusted-Only loader attempted to load sandboxed resource from "+ url"

  The following two SecurityExceptions are thrown when mixed components are first detected and a decision is made to disallow mixing. In the first case, everything previosly loaded was trusted and then an attempt was made to load an untrusted component. The second case is the reverse condition.

  trusted loader attempted to load sandboxed resource from "+ url" sandboxed loader attempted to load trusted resource from "+ url"

  The following two SecurityExceptions are thrown after mixed components had previously been detected and a decision was made to allow them to coexist. The exceptions indicate that a component name collision (resource name or class package name) was detected between trusted and untrusted components and the request to load the resource or class was denied.

  "resource \"" + name + "\" does not match trust level of other resources of the same name" "class \"" + packageName + "\" does not match trust level of other classes in the same package"

  The following two SecurityExceptions are thrown when untrusted components have been previously accessed, an attempt to load a trusted component was previously detected, and a decision was made to allow mixed components to coexist, and a jar containing trusted components is opened and a component name collision is detected between trusted and untrusted components.

  "untrusted resource \"" + name + "\" in class path" "untrusted class package \"" + packageName + "\" in class path"

• Question: I have a mixed code Java Web Start application which cannot be easily updated to use the Trusted-Library manifest attribute. Can I sign the jar files in the sandboxed JNLP without having to change the JNLP to request the all-permissions security model?

  Answer: Yes, with some limitations beginning with Java Web Start in Java SE or Java for Business Update 21. The sandboxed jar files must be signed in the same way (same signing certificates) as one or more of the trusted jar files in a JNLP file that uses the all-permissions security model, and the trusted jar file must be opened by Java Web Start prior to any sandboxed resource being loaded which shares the same signer. This means the trusted jar file must be earlier in Java Web Start's jar search order or it is triggered to load independent of the simple search order by use of the jar indexing feature. In Java Web Start, the main application JNLP's jars are searched first, followed in declaration order by any JNLP extensions. Jar files labeled within a JNLP as "eager" are searched first, followed by "lazy" jar files, followed by any jar files labeled as using the "part" feature.

• Question: I have Java on my phone. Is that affected by this issue?

  Answer: No, Java ME is not affected.

Original Page: http://pocket.co/sGvc9

Shared from Pocket

^ed