CVE-2026-63337 RabbitMQ Java client: Unvalidated Class.forName in JSON-RPC ProcedureDescription enables arbitrary class loading
An attacker can trigger arbitrary class loading and static initializer execution in the RabbitMQ Java client by manipulating JSON-RPC responses, leading to code execution or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-63337?
CVE-2026-63337 is a high-severity code injection vulnerability in rabbitmq-java-client, published on 18 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-470
Which versions are affected by CVE-2026-63337?
2 open source packages ship an affected version, including com.rabbitmq:amqp-client.
| Package | Affected | Fixed in |
|---|---|---|
com.rabbitmq:amqp-client Maven | All versions | 5.33.0 |
com.rabbitmq:amqp-client Maven | All versions | 5.33.0 |
How do I fix CVE-2026-63337?
Upgrade com.rabbitmq:amqp-client to 5.33.0 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-63337 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63337 exists.
Sources
Also known as CLEANSTART-2026-ED93010, DEBIAN-CVE-2026-63337, ECHO-7592-392e-0fc2, GHSA-6g32-pxv4-2wfj, MINI-3fwg-j683-4hc8, MINI-3j57-xv6x-cf6w and 15 more.