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High, CVSS 7.5amended

RabbitMQ Java client: Unvalidated Class.forName in JSON-RPC ProcedureDescription enables arbitrary class loading

CVE-2026-63337GHSA-6g32-pxv4-2wfj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (com.rabbitmq:amqp-client 5.33.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.5 · 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 · score source
EPSS
  • CVE-2026-63337: 0.56% estimated exploitation activity in the next 30 days; percentile 46.46 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-6g32-pxv4-2wfj

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-6g32-pxv4-2wfj

Agent brief

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# Patch Next advisory brief: CVE-2026-63337

Advisory: RabbitMQ Java client: Unvalidated Class.forName in JSON-RPC ProcedureDescription enables arbitrary class loading
IDs: CVE-2026-63337, GHSA-6g32-pxv4-2wfj
Record: https://patchnext.com/advisories/cve-2026-63337 (revision 3, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: com.rabbitmq:amqp-client 5.33.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven com.rabbitmq:amqp-client: affected < 5.33.0; fixed in 5.33.0

## Suggested inspection (read-only)
- Maven com.rabbitmq:amqp-client: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on com.rabbitmq:amqp-client.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-6g32-pxv4-2wfj (OSV record GHSA-6g32-pxv4-2wfj lists affected ranges: Maven com.rabbitmq:amqp-client >=0 <5.33.0 (fixed))
- Verified: https://github.com/advisories/GHSA-6g32-pxv4-2wfj (GitHub-reviewed advisory GHSA-6g32-pxv4-2wfj lists affected ranges: Maven com.rabbitmq:amqp-client >=0 <5.33.0)

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