RabbitMQ amqp091-go: Silent Data Truncation and State Corruption via Shortstr Integer Overflow

Summary

A data integrity and protocol corruption vulnerability exists in the AMQP client's property serialization logic. When encoding AMQP short string (shortstr) fields—such as identifiers, routing strings, and content metadata—the length of the string is explicitly cast to a fixed-size 8-bit unsigned integer (uint8).

If an application provides a property string exceeding 255 bytes, the length counter silently wraps around (e.g., a length of 300 wraps to 44). As a result, the parser writes only a truncated portion of the string into the outgoing connection buffer without returning an error. This leads to silent data corruption, broken RPC routing, and unpredictable broker-side state behavior.

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Vulnerability Details

Mechanism

The vulnerability resides in the wire-level serialization logic for application publishing properties:

// write.go:246
length := uint8(len(b))  // wraps silently when len(b) > 255 (e.g., 300 -> 44)

Because Go allows silent integer truncation during explicit type casting, lengths larger than $2^8 - 1$ lose their most significant bits. The underlying stream writer reads length to determine how many bytes to pull from the buffer. Because no error or boundary check accompanies this truncation, the application believes the full payload was transmitted successfully.

Affected Properties

This truncation behavior affects every standard AMQP field serialized as a shortstr:

• CorrelationId
• ReplyTo
• MessageId
• Expiration
• UserId
• AppId
• ContentType
• ContentEncoding
• Type

Impact

The critical consequence is silent protocol desynchronization at the application layer. The underlying TCP stream remains framed properly (because the shortened length matches the bytes written), but the business logic is corrupted. Distributed transactions, request-reply correlations, and tracing headers are truncated, causing downstream systems to drop messages or route them to incorrect consumers.

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Attack Vector

An attacker who can influence metadata fields processed by an upstream application (such as a user-supplied tracking ID or a long content-type header) can exploit this to break system components:

1. Targeting RPC Routing: A user passes a malicious or overly long CorrelationId of 300 bytes through an application endpoint.
2. Silent Truncation: The library wraps the length value to 44, transmitting only the first 44 bytes to the rabbitMQ broker.
3. Broken Correlation: When the service processes the request and responds, the replying consumer attempts to route the message using the full 300-byte identifier. Because the broker only recognizes the truncated 44-byte ID, the reply loop breaks silently, leading to hanging processes or data leaks across transaction boundaries.