ActiveMQ can send/receive JMS Object messages (ObjectMessage in ActiveMQ context) to comply with JMS specifications. Internally, ActiveMQ relies on Java’s serialization mechanism for the marshaling and unmarshalling of the messages' payload.

Applications should restrict the types that can be unserialized from JMS messages.

## Why is this an issue?

When the application does not implement controls over the JMS object types, its clients could be able to force the deserialization of arbitrary objects. This may lead to deserialization injection attacks.

### What is the potential impact?

Attackers will be able to force the deserialization of arbitrary objects. This process will trigger the execution of magic unmarshalling methods on the object and its properties. With a specially crafted serialized object, the attackers can exploit those magic methods to achieve malicious purposes.

While the exact impact depends on the types available in the execution context at the time of deserialization, such an attack can generally lead to the execution of arbitrary code on the application server.

#### Application-specific attacks

By exploiting the behavior of some of the application-defined types and objects, the attacker could manage to affect the application’s business logic. The exact consequences will depend on the application’s nature:

- Payment bypass in an e-commerce application.
- Privilege escalation.
- Unauthorized users' data access.

#### Publicly-known exploitation

In some cases, depending on the library the application uses and their versions, there may exist publicly known deserialization attack payloads known as gadget chains. In general, they are designed to have severe consequences, such as:

- Arbitrary code execution
- Arbitrary file read or write
- Server-side request forgery

Those attacks are independent of the application’s own logic and from the types it specifies.

## How to fix it in Java EE

### Code examples

The following code example is vulnerable to a deserialization injection attack because it allows the deserialization of arbitrary types from JMS messages.

#### Noncompliant code example

    ActiveMQConnectionFactory factory = new ActiveMQConnectionFactory("tcp://localhost:61616");
    factory.setTrustAllPackages(true); // Noncompliant

#### Compliant solution

    ActiveMQConnectionFactory factory = new ActiveMQConnectionFactory("tcp://localhost:61616");
    factory.setTrustedPackages(Arrays.asList("org.mypackage1", "org.mypackage2"));

### How does this work?

The noncompliant code example calls the `setTrustAllPackages` method that explicitly allows the deserialization of arbitrary types. On the contrary, the compliant code example, thanks to the `setTrustedPackages` method, defines a short list of classes allowed for the deserialization.

While defining a short list of trusted types is generally the state-of-the-art solution to avoid deserialization injection attacks, it is important to ensure that the allowed classes and packages can not be used to exploit the issue. In that case, a vulnerability would still be present.

Note that ActiveMQ, starting with version 5.12.2, forces developers to explicitly list packages that JMS messages can contain. This limits the risk of successful exploitation. In versions before that one, calling the `ActiveMQConnectionFactory` constructor without further configuration would leave the application at risk.

## Resources

### Documentation

- Apache ActiveMQ Documentation - ObjectMessage
- CVE - CVE-2015-5254

### Standards

- OWASP - Top 10 2021 - Category A8 - Software and Data Integrity Failures
- OWASP - Top 10 2017 - Category A8 - Insecure Deserialization
- CWE - CWE-502 - Deserialization of Untrusted Data