Mitigating serialization issues in AEM mitigating-serialization-issues-in-aem

AEM 6.4 has reached the end of extended support and this documentation is no longer updated. For further details, see our technical support periods. Find the supported versions here.

Overview overview

The AEM team at Adobe has been working closely with the open source project NotSoSerial to assist in mitigating the vulnerabilities described in CVE-2015-7501. NotSoSerial is licensed under the Apache 2 license and includes ASM code licensed under its own BSD-like license.

The agent jar included with this package is Adobe’s modified distribution of NotSoSerial.

NotSoSerial is a Java level solution to a Java level problem and is not AEM specific. It adds a preflight check to an attempt to deserialize an object. This check will test a class name against a firewall-style allow list and/or block list. Due to the limited number of classes in the default block list, this is unlikely to have an impact on your systems or code.

By default, the agent will perform a block list check against current known vulnerable classes. This block list is intended to protect you from the current list of exploits that use this type of vulnerability.

The block list and allow list can be configured by following the instructions in the Configuring the Agent section of this article.

The agent is intended to help mitigate the latest known vulnerable classes. If your project is deserializing untrusted data, it may still be vulnerable to denial of service attacks, out of memory attacks, and unknown future deserialization exploits.

Adobe officially supports Java 6, 7, and 8, however our understanding is that NotSoSerial supports Java 5 as well.

Installing the Agent installing-the-agent

If you have previously installed the serialization hotfix for AEM 6.1, please remove the agent start commands from your java execution line.
  1. Install the com.adobe.cq.cq-serialization-tester bundle.

  2. Go to the Bundle Web Console at https://server:port/system/console/bundles

  3. Look for the serialization bundle and start it. This should dynamically autoload the NotSoSerial agent.

Installing the Agent on Application Servers installing-the-agent-on-application-servers

The NotSoSerial agent is not included in the stardard distribution of AEM for application servers. However, you can extract it from the AEM jar distribution and use it with your application server setup:

  1. First, download the AEM quickstart file and extract it:

    code language-shell
    java -jar aem-quickstart-6.2.0.jar -unpack
  2. Go to the location of the newly unzipped AEM quickstart, and copy the crx-quickstart/opt/notsoserial/ folder to the crx-quickstart folder of the AEM application server installation.

  3. Change the ownership of /opt to the user running the server:

    code language-shell
    chown -R opt <user running the server>
  4. Configure and check that the agent has been properly activated as shown in the following sections of this article.

Configuring the agent configuring-the-agent

The default configuration is adequate for most installs. This includes a block list of known remote execution vulnerable classes and a allow list of packages where deserialization of trusted data should be relatively safe.

The firewall configuration is dynamic, and can be changed at any time by:

  1. Going to the Web Console at https://server:port/system/console/configMgr

  2. Searching for and clicking Deserialization Firewall Configuration.

    note note
    You can also reach the configuration page directly by accessing the URL at:
    • https://server:port/system/console/configMgr/com.adobe.cq.deserfw.impl.DeserializationFirewallImpl

This configuration contains the allow list, block list, and deserialization logging.

Allow listing

In the allow listing section, these are classes or package prefixes that will be allowed for deserialization. It is important to be aware that if you are deserializing classes of your own, you will need to add either the classes or packages to this allow list.

Block listing

In the block listing section are classes that are never allowed for deserializaiton. The initial set of these classes is limited to classes that have been found vulnerable to remote execution attacks. The block list is applied before any allow listed entries.

Diagnostinc Logging

In the section for diagnostic logging, you can chose several options to log when deserialization is taking place. These are only logged on first use, and are not logged again on subsequent uses.

The default of class-name-only will inform you of the classes that are being deserialized.

You can also set the full-stack option which will log a java stack of the first deserialization attempt to inform you where your deserialization is taking place. This can be useful for finding and removing deserialization from your usage.

Verifying the Agent’s Activation verifying-the-agent-s-activation

You can verify the deserialization agent’s configuration by browsing to the URL at:

  • https://server:port/system/console/healthcheck?tags=deserialization

Once you access the URL, a list of health checks related to the agent will be displayed. You can determine if the agent is properly activated by verifying that the health checks are passing. If they are failing, you may need to load the agent manually.

For more information on troubleshooting issues with the agent, see Handling Errors With Dynamic Agent Loading below.

If you add org.apache.commons.collections.functors to the allow list, the health check will always fail.

Handling errors with dynamic agent loading handling-errors-with-dynamic-agent-loading

If errors are exposed in the log, or the verification steps detect a problem loading the agent, you might need to load the agent manually. This is also recommended in case you are using a JRE (Java Runtime Environment) instead of a JDK (Java Development Toolkit), since the tools for dynamic loading are not available.

In order to load the agent manually, follow the below instructions:

  1. Modify the JVM startup parameters of the CQ jar, adding the following option:

    code language-shell
    note note
    This requires using the -nofork CQ/AEM option as well, along with the appropriate JVM memory settings, as the agent won’t be enabled on a forked JVM.
    note note
    The Adobe distribution of the NotSoSerial agent jar can be found in the crx-quickstart/opt/notsoserial/ folder of your AEM installation.
  2. Stop and restart the JVM;

  3. Verify the agent’s activation again by following the steps described above in Verifying The Agent’s Activation.

Other Considerations other-considerations

If you are running on an IBM JVM, please review the documentation on support for the Java Attach API at this location.