CVE-2026-63337: RabbitMQ Java client Unvalidated Class.forName Vulnerability
HIGHCVE-2026-63337 is a HIGH unvalidated class.forname vulnerability (CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')) affecting RabbitMQ Java client libraries in the Maven ecosystem. The issue involves unvalidated class.forname in json-rpc proceduredescription enables arbitrary class loading. Remediation is available by upgrading affected packages to version 5.33.0.
CVE-2026-63337 at a Glance
How to Fix CVE-2026-63337
To remediate this vulnerability, upgrade all affected RabbitMQ Java client dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
<dependency>
<groupId>com.rabbitmq</groupId>
<artifactId>amqp-client</artifactId>
<version>5.33.0</version>
</dependency>Run the following command in your project directory to verify that all resolved dependencies use the patched release:
mvn dependency:tree -Dincludes=com.rabbitmqHow to Check if You Are Affected
To determine whether your Java application is affected by CVE-2026-63337, inspect your build dependencies using the Maven Dependency Plugin:
mvn dependency:tree -Dincludes=com.rabbitmqAnalyze the terminal output to locate any version of RabbitMQ Java client in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 5.33.0), your application is affected.
Note: The mvn dependency:tree -Dincludes=com.rabbitmq command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection'), where the product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code. In RabbitMQ Java client, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-63337 Affected RabbitMQ Java client Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
com.rabbitmq:amqp-client
|
Maven |
< 5.33.0
|
5.33.0
|
References
Frequently Asked Questions
What is CVE-2026-63337?
Which RabbitMQ Java client versions are affected?
What version fixes CVE-2026-63337?
Is amqp-client affected?
What CWE is associated with CVE-2026-63337?
How can I check Maven dependencies for CVE-2026-63337?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-6g32-pxv4-2wfj",
"modified" : "2026-08-18T16:32:29Z",
"published" : "2026-08-18T16:32:29Z",
"aliases" : [ "CVE-2026-63337" ],
"summary" : "RabbitMQ Java client: Unvalidated Class.forName in JSON-RPC ProcedureDescription enables arbitrary class loading",
"details" : "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.\n\n**Vulnerable code** (`ProcedureDescription.java:101-127`):\nWhen 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)`.\n\n**Attack scenario:**\n1. Victim uses `JsonRpcClient` to connect to a JSON-RPC service via RabbitMQ\n2. Attacker (co-tenant on shared broker, or MITM) intercepts the `system.describe` request\n3. Attacker responds with crafted `javaReturnType` values\n4. Victim's client calls `Class.forName(attackerInput)` with default `initialize=true`\n5. Static initializers of attacker-specified classes execute in victim's JVM\n\nAdditionally, the loaded class from `getReturnType()` is passed to `mapper.parse(replyStr, expectedType)` at `JsonRpcClient.java:168`, potentially enabling type-confusion.\n\n**Recommended fix:** Use `Class.forName(javaReturnType, false, classLoader)` to prevent static initializer execution, or add an allowlist of permitted return types.\n\n**CWE:** CWE-470\n\n---\n\n**Reply from reporter (2026-06-29):** Thanks for the quick turnaround. Fix looks good. Looking forward to the CVE assignment.",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Maven",
"name" : "com.rabbitmq:amqp-client"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "5.33.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/security/advisories/GHSA-6g32-pxv4-2wfj"
}, {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/pull/2000"
}, {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/pull/2002"
}, {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/commit/0032f75f9dc3df847f94b2b85a16119250bf63cb"
}, {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/commit/9f8e7efd0c648f235dc0e96232ae7efa75ea4fa8"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client"
}, {
"type" : "WEB",
"url" : "https://github.com/rabbitmq/rabbitmq-java-client/releases/tag/v5.33.0"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-470" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-08-18T16:32:29Z",
"nvd_published_at" : null
}
}