{"id":"CVE-2026-63335","aliases":["GHSA-qx7j-jv8m-fppr"],"url":"https://o3.security/vulnerability/CVE-2026-63335","summary":"RabbitMQ Java client malformed body frame triggers raw command assembler exception","details":"### Summary\nRabbitMQ 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. \n\nThis was discovered based on an existing vulnerability CVE-2017-15699.\n\n### Details\nInbound 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`).\n\n### PoC\n[poc.zip](https://github.com/user-attachments/files/28182717/poc.zip)\n\n```bash\nbash ./poc/run.sh\n```\n\n```text\nException in thread \"main\" java.lang.UnsupportedOperationException: %%%%%% FIXME unimplemented\n```\n\nThe `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.\n\n### Impact\nThe 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.","published":"2026-08-18T16:20:08.128Z","modified":"2026-09-12T08:08:19.042933Z","cvss":null,"epss":{"score":0.00372,"percentile":0.30897,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"com.rabbitmq:amqp-client","fixedVersion":"5.31.0"}],"fix":{"url":"https://github.com/rabbitmq/rabbitmq-java-client/commit/31735344d9f9dfc53740b67f06e560e8846b9322","label":"rabbitmq/rabbitmq-java-client@3173534"},"references":[{"type":"WEB","url":"https://github.com/rabbitmq/rabbitmq-java-client/releases/tag/v5.31.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63335.json"},{"type":"ADVISORY","url":"https://github.com/rabbitmq/rabbitmq-java-client/security/advisories/GHSA-qx7j-jv8m-fppr"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63335"},{"type":"FIX","url":"https://github.com/rabbitmq/rabbitmq-java-client/commit/31735344d9f9dfc53740b67f06e560e8846b9322"},{"type":"FIX","url":"https://github.com/rabbitmq/rabbitmq-java-client/commit/abd6d60d4e2bfc1a327dc90ab246b2e8aca1f33b"},{"type":"FIX","url":"https://github.com/rabbitmq/rabbitmq-java-client/pull/1959"},{"type":"FIX","url":"https://github.com/rabbitmq/rabbitmq-java-client/pull/1960"},{"type":"PACKAGE","url":"https://github.com/rabbitmq/rabbitmq-java-client"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-12T08:08:19.042933Z"}}