Executive brief
RabbitMQ's Java AMQP client library contains a vulnerability in its message parsing code that can be exploited by a malicious server to crash the entire JVM. When processing string or binary data fields from AMQP protocol messages, the library allocates memory based on a size value sent by the server without validating whether that size is reasonable. An attacker can declare a ~2 GB string field, forcing the JVM to attempt a massive memory allocation that exceeds available resources, resulting in an out-of-memory crash that brings down any application using this library.
Technical details
The vulnerability exists in the `ValueReader.readBytes()` method in `src/main/java/com/rabbitmq/client/impl/ValueReader.java`. The method reads a 32-bit integer from the wire to determine the size of a byte array, then immediately allocates that array without validating the size against frame boundaries or the negotiated maximum frame size (default 131,072 bytes). A malicious AMQP server sends a LongString field (AMQP type tag 'S') with declared length 0x7FFFFFFE (2,147,483,646 bytes), which passes the check `contentLength < Integer.MAX_VALUE` and triggers `new byte[2147483646]`, causing an OutOfMemoryError before the `readFully()` call ever attempts to read data. This vulnerability is exploitable pre-authentication via the `connection.start` server-properties table, requiring only network access to an AMQP broker. The fix validates the declared content length against the frame's remaining bytes or maximum frame size before allocating memory. Patched in version 5.33.1.
Affected products
- RabbitMQ amqp-client <= 5.33.0
Timeline
- 2026-07-09: disclosed: GitHub Security Advisory published
- 2026-08-18: advisory: Updated in GitHub Advisory Database
- 2026-08-18: patched: Version 5.33.1 released with fix
References
- https://api.github.com/users/lucianjohnhouse
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- https://api.github.com/users/lucianjohnhouse/repos
- https://avatars.githubusercontent.com/u/244141656?v=4
- https://api.github.com/users/lucianjohnhouse/events%7B/privacy%7D