CVE-2026-63335: RabbitMQ Java client malformed body frame triggers raw command assembler exception
Summary RabbitMQ Java Client's inbound AMQP command assembly accepts a content header declaring a small body and then processes a larger body frame by throwing a raw UnsupportedOperationException from CommandAssembler. A broker peer that the client has connected to can use this malformed frame sequence to fail frame processing and tear down the client connection instead of receiving a clean protocol-level malformed-frame error.
This was discovered based on an existing vulnerability CVE-2017-15699.
Details Inbound frames enter the client through SocketFrameHandler.readFrame, which returns frames parsed from the peer-controlled input stream (src/main/java/com/rabbitmq/client/impl/SocketFrameHandler.java:197). AMQConnection.MainLoop reads each frame (src/main/java/com/rabbitmq/client/impl/AMQConnection.java:692) and dispatches non-zero-channel frames to the channel while the connection is open (src/main/java/com/rabbitmq/client/impl/AMQConnection.java:748 and src/main/java/com/rabbitmq/client/impl/AMQConnection.java:766). The channel then passes the frame to the current command assembler through AMQChannel.handleFrame and AMQCommand.handleFrame (src/main/java/com/rabbitmq/client/impl/AMQChannel.java:121, src/main/java/com/rabbitmq/client/impl/AMQCommand.java:114). When a content-bearing method is followed by a content header, CommandAssembler.consumeHeaderFrame records the header's declared body size in remainingBodyBytes after only checking it against the configured maximum (src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:126 through src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:139). The body-frame path subtracts the received payload length from that remaining count before validating that the payload fits (src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:145 through src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:149), so a body frame larger than the declared size drives the count negative and reaches the raw UnsupportedOperationException at src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:150 and src/main/java/com/rabbitmq/client/impl/CommandAssembler.java:151. AMQConnection catches the resulting throwable in frame processing and performs connection failure handling and final shutdown (src/main/java/com/rabbitmq/client/impl/AMQConnection.java:695 through src/main/java/com/rabbitmq/client/impl/AMQConnection.java:705).
PoC poc.zip
bash bash ./poc/run.sh
text Exception in thread "main" java.lang.UnsupportedOperationException: %%%%%% FIXME unimplemented
The UnsupportedOperationException: %%%%%% FIXME unimplemented fingerprint is the raw exception thrown at the negative remainingBodyBytes check in CommandAssembler.consumeBodyFrame. This line shows the malformed declared-size/body-size sequence reached the vulnerable assembler path.
Impact The attacker model is a remote AMQP broker peer that the RabbitMQ Java Client application has accepted, including a malicious broker endpoint, a compromised broker, or routing that sends the client to an attacker-controlled peer. The peer needs a non-zero open channel that can receive a content-bearing server-to-client method such as basic.deliver, then sends the method frame, a content header declaring a body below the configured maximum, and a body frame whose payload exceeds that declared size. Under those conditions, the peer can force frame processing to fail with UnsupportedOperationException and close the AMQP connection, producing a client-side denial of service for work depending on that connection; the finding does not indicate memory corruption, data disclosure, or code execution.
Other sources
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.FRAMEBODY 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.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/com.rabbitmq:amqp-clientto a version that resolves this vulnerability.Fixed in 5.31.0 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 5.31.0
Event History
Frequently Asked Questions
Which deployments are realistically exposed?
Applications using RabbitMQ Java client versions before 5.31.0 are affected when they process frames from a malicious or compromised RabbitMQ broker peer. The impact is limited to work using the connection that receives the malformed frame sequence.
What access is required to trigger the denial of service?
An attacker needs the ability to act as, control, or compromise a broker peer and send a malformed AMQP sequence on an open nonzero channel. The sequence uses a content-bearing method and header with a remaining body size smaller than a subsequent body-frame payload.
What version fixes the issue?
Upgrade the RabbitMQ Java client to version 5.31.0, which changes handling of this malformed input.
How would this appear in an affected application?
Affected connections can terminate frame processing and close after receiving the malformed sequence, interrupting work assigned to that connection. The reported behavior is a raw UnsupportedOperationException rather than a MalformedFrameException.