How severe is CVE-2026-63337?

No CVSS score has been assigned to CVE-2026-63337 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-63337?

CVE-2026-63337 affects the following packages: com.rabbitmq:amqp-client (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-63337?

Update com.rabbitmq:amqp-client to 5.33.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63337 is resolved across your whole dependency graph.

How do I detect CVE-2026-63337 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.rabbitmq:amqp-client, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-63337 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-63337 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-63337 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-63337?

CVE-2026-63337 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 44th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-63337?

CVE-2026-63337 is classified as CWE-470 (CWE-470). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-63337 published, and has it been updated?

CVE-2026-63337 was published on August 18, 2026 and was last updated on September 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

Not in CISA KEV

CVE-2026-63337 — amqp-client

Fix: rabbitmq/rabbitmq-java-client@0032f75

CVE-2026-63337 is a CWE-470 vulnerability in com.rabbitmq:amqp-client. A fix is available for com.rabbitmq:amqp-client — see the affected versions and patch details below.

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

Also known asGHSA-6g32-pxv4-2wfj

Published

Aug 18, 2026

Updated

Sep 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-63337.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs44th percentile — riskier than 44% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

☕com.rabbitmq:amqp-client

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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:

Victim uses JsonRpcClient to connect to a JSON-RPC service via RabbitMQ
Attacker (co-tenant on shared broker, or MITM) intercepts the system.describe request
Attacker responds with crafted javaReturnType values
Victim's client calls Class.forName(attackerInput) with default initialize=true
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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`com.rabbitmq:amqp-client`	all versions	5.33.0`com.rabbitmq:amqp-client:5.33.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.rabbitmq:amqp-client, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update com.rabbitmq:amqp-client to 5.33.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63337 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

Red Hat has evaluated this vulnerability as Important because an attacker with access to the messaging transport can trigger arbitrary class initialization and execution in the host JVM without requiring privileged access. The risk is elevated in multi-tenant message broker environments where untrusted actors can…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-63337 (CC BY 4.0)

Frequently Asked Questions

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 sce

O3 Security · Impact-Aware SCA

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