CVE-2026-63337

The RabbitMQ Java client library allows Java and JVM-based applications to connect to and interact with RabbitMQ nodes. Prior to 5.33.0, com.rabbitmq.tools.jsonrpc.ProcedureDescription receives a javaReturnType value in an untrusted system.describe response and passes it through JSONUtil.tryFill, setJavaReturnType, and computeReturnTypeAsJavaClass to Class.forName(javaReturnType) with initialization enabled. An attacker able to answer the JsonRpcClient request through a shared broker or network interception can select a class already present in the victim JVM and trigger its static initializer, while JsonRpcClient.java later passes getReturnType output to mapper.parse and may also create type confusion. Successful exploitation can affect confidentiality, integrity, and availability in the client process. This issue is fixed in version 5.33.0.

The RabbitMQ Java client library allows Java and JVM-based applications to connect to and interact with RabbitMQ nodes. Prior to 5.33.0, com.rabbitmq.tools.jsonrpc.ProcedureDescription receives a javaReturnType value in an untrusted system.describe response and passes it through JSONUtil.tryFill, setJavaReturnType, and computeReturnTypeAsJavaClass to Class.forName(javaReturnType) with initialization enabled. An attacker able to answer the JsonRpcClient request through a shared broker or network interception can select a class already present in the victim JVM and trigger its static initializer, while JsonRpcClient.java later passes getReturnType output to mapper.parse and may also create type confusion. Successful exploitation can affect confidentiality, integrity, and availability in the client process. This issue is fixed in version 5.33.0.

The JSON-RPC tools in `com.rabbitmq.tools.jsonrpc` perform `Class.forName(javaReturnType)` with `initialize=true` on class names received from untrusted AMQP messages, without any validation or allowlist. **Vulnerable code** (`ProcedureDescription.java:101-127`): When a `JsonRpcClient` connects, it calls `system.describe` and receives a service description from the AMQP queue. The response JSON includes `javaReturnType` fields that are reflectively set via `JSONUtil.tryFill()`, triggering `setJavaReturnType()` → `computeReturnTypeAsJavaClass()` → `Class.forName(javaReturnType)`. **Attack scenario:** 1. Victim uses `JsonRpcClient` to connect to a JSON-RPC service via RabbitMQ 2. Attacker (co-tenant on shared broker, or MITM) intercepts the `system.describe` request 3. Attacker responds with crafted `javaReturnType` values 4. Victim's client calls `Class.forName(attackerInput)` with default `initialize=true` 5. Static initializers of attacker-specified classes execute in victim's JVM Additionally, the loaded class from `getReturnType()` is passed to `mapper.parse(replyStr, expectedType)` at `JsonRpcClient.java:168`, potentially enabling type-confusion. **Recommended fix:** Use `Class.forName(javaReturnType, false, classLoader)` to prevent static initializer execution, or add an allowlist of permitted return types. **CWE:** CWE-470 --- **Reply from reporter (2026-06-29):** Thanks for the quick turnaround. Fix looks good. Looking forward to the CVE assignment.

The JSON-RPC tools in `com.rabbitmq.tools.jsonrpc` perform `Class.forName(javaReturnType)` with `initialize=true` on class names received from untrusted AMQP messages, without any validation or allowlist. **Vulnerable code** (`ProcedureDescription.java:101-127`): When a `JsonRpcClient` connects, it calls `system.describe` and receives a service description from the AMQP queue. The response JSON includes `javaReturnType` fields that are reflectively set via `JSONUtil.tryFill()`, triggering `setJavaReturnType()` → `computeReturnTypeAsJavaClass()` → `Class.forName(javaReturnType)`. **Attack scenario:** 1. Victim uses `JsonRpcClient` to connect to a JSON-RPC service via RabbitMQ 2. Attacker (co-tenant on shared broker, or MITM) intercepts the `system.describe` request 3. Attacker responds with crafted `javaReturnType` values 4. Victim's client calls `Class.forName(attackerInput)` with default `initialize=true` 5. Static initializers of attacker-specified classes execute in victim's JVM Additionally, the loaded class from `getReturnType()` is passed to `mapper.parse(replyStr, expectedType)` at `JsonRpcClient.java:168`, potentially enabling type-confusion. **Recommended fix:** Use `Class.forName(javaReturnType, false, classLoader)` to prevent static initializer execution, or add an allowlist of permitted return types. **CWE:** CWE-470 --- **Reply from reporter (2026-06-29):** Thanks for the quick turnaround. Fix looks good. Looking forward to the CVE assignment.

La biblioteca cliente Java de RabbitMQ permite a las aplicaciones Java y basadas en JVM conectarse e interactuar con nodos RabbitMQ. Antes de la versión 5.33.0, com.rabbitmq.tools.jsonrpc.ProcedureDescription recibe un valor javaReturnType en una respuesta system.describe no confiable y lo pasa a través de JSONUtil.tryFill, setJavaReturnType y computeReturnTypeAsJavaClass a Class.forName(javaReturnType) con la inicialización habilitada. Un atacante capaz de responder a la solicitud de JsonRpcClient a través de un intermediario compartido o una intercepción de red puede seleccionar una clase ya presente en la JVM de la víctima y activar su inicializador estático, mientras que JsonRpcClient.java posteriormente pasa la salida de getReturnType a mapper.parse y también puede crear confusión de tipos. La explotación exitosa puede afectar la confidencialidad, la integridad y la disponibilidad en el proceso del cliente. Este problema está solucionado en la versión 5.33.0.