CVE-2026-63335 in Java Client
Summary
by MITRE • 08/18/2026
The RabbitMQ Java client library allows Java and JVM-based applications to connect to and interact with RabbitMQ nodes. Prior to 5.31.0, inbound AMQP command assembly in src/main/java/com/rabbitmq/client/impl/CommandAssembler.java processes a content-bearing method and header whose remainingBodyBytes value is smaller than a following AMQP.FRAME_BODY payload. CommandAssembler.consumeBodyFrame subtracts the peer-controlled payload length before validating that it fits, drives remainingBodyBytes negative, and throws a raw UnsupportedOperationException instead of MalformedFrameException. A malicious or compromised broker peer can send this malformed sequence on an open nonzero channel to terminate frame processing and close the client connection, causing denial of service for work using that connection. This issue is fixed in version 5.31.0.
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Analysis
by VulDB Data Team • 08/18/2026
The RabbitMQ Java client library serves as a critical component for enabling Java and JVM-based applications to establish connections with RabbitMQ message broker nodes. In versions prior to 5.31.0, the library contains a significant vulnerability within its inbound AMQP command assembly logic, specifically located in the CommandAssembler class. This flaw arises during the processing of content-bearing methods and headers where the remainingBodyBytes value is smaller than the length of a subsequent AMQP.FRAME_BODY payload sent by the peer. The core technical issue lies in the order of operations performed by the consumeBodyFrame method, which subtracts the peer-controlled payload length from the remaining body bytes before validating whether the data fits within expected bounds. This sequence allows an attacker to manipulate the internal state variables such that remainingBodyBytes becomes negative, triggering a raw UnsupportedOperationException rather than the intended MalformedFrameException.
This implementation error creates a direct path for denial of service attacks against applications relying on the RabbitMQ Java client. A malicious or compromised broker peer can exploit this flaw by sending a specifically crafted malformed sequence over an open nonzero channel. Upon receiving this payload, the client library fails to handle the exception gracefully and instead terminates frame processing abruptly. This results in the immediate closure of the client connection, effectively disrupting any ongoing work that depends on that specific communication link. The impact is severe for production environments where reliable message delivery is paramount, as it allows an external actor to force disconnections without requiring authentication or prior compromise of the application logic itself.
From a security classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-754: Improper Check for Unusual or Exceptional Conditions. The failure to validate input lengths before performing arithmetic operations on state variables represents a classic buffer handling error that leads to unexpected control flow termination. In the context of the MITRE ATT&CK framework, this behavior is consistent with T1499 Endpoint Denial of Service, as it leverages protocol-level interactions to exhaust resources or disrupt service availability for specific endpoints. The lack of proper exception handling means that the application may crash or enter an unstable state if not explicitly wrapped in try-catch blocks designed to handle low-level library exceptions, which is often overlooked by developers assuming standard AMQP compliance from the broker side.
Mitigation strategies primarily involve upgrading the RabbitMQ Java client library to version 5.31.0 or later, where this logic has been corrected to validate payload lengths before subtraction and ensure that appropriate MalformedFrameException types are thrown for invalid inputs. For organizations unable to upgrade immediately due to dependency constraints, implementing strict network-level filtering can provide temporary relief by blocking traffic from untrusted broker peers or enforcing AMQP protocol compliance at the gateway level. Additionally, application developers should review their connection handling logic to include robust exception management that catches low-level library exceptions and implements reconnection strategies with exponential backoff to mitigate the impact of sudden disconnections caused by such vulnerabilities in future versions.