amqp091-go is a Go AMQP 0.9.1 client. From 1.13.0 until 1.14.0, the frame-size mitigation from the prior allocation advisory can be bypassed before connection.tune completes because Connection.maxFrameSize uses zero for both the not-yet-negotiated and negotiated-unlimited states. A malicious or compromised AMQP peer can send a short body-frame header with a large declared payload length, causing ReadFrame and the body-frame parser to allocate attacker-selected memory before the payload is received or the frame's protocol state is rejected. The condition is reachable through public Open even when Config.FrameSize is set to the protocol minimum and can cause severe memory pressure, out-of-memory termination, or loss of the client process before authentication completes. This issue is fixed in version 1.14.0.

Affected: Go: github.com/rabbitmq/amqp091-go

## Summary The frame-size mitigation released in `amqp091-go` v1.13.0 can be bypassed before `connection.tune` completes. A malicious or compromised AMQP peer can send only a seven-byte body-frame header containing a large attacker-controlled `uint32` payload length. The client allocates a slice of that declared length before it verifies that the payload exists or rejects the frame for its invalid protocol state.

The bypass occurs because `Connection.maxFrameSize` starts at zero. The reader interprets zero as both “negotiated unlimited” and “not negotiated yet,” and skips the pre-allocation size check in either case. `Open` starts the reader goroutine before negotiation and does not store a limit until after it receives `connection.tune`.

This remains reachable even if the caller explicitly uses `Config{FrameSize: frameMinSize}`. A malicious broker can therefore cause excessive memory allocation, potentially terminating the Go client process through memory exhaustion, before authentication and connection setup complete.

## Relationship to the existing advisory

[GHSA-r9c8-gcjp-xfwh](https://github.com/rabbitmq/amqp091-go/security/advisories/GHSA-r9c8-gcjp-xfwh) describes attacker-controlled, unbounded allocation by a malicious broker and identifies v1.13.0 as the patched version. [Pull request 369](https://github.com/rabbitmq/amqp091-go/pull/369) added a frame-size check before parser allocation, but the check is active only when the stored maximum is nonzero.

The v1.13.…

github.com/rabbitmq/amqp091-go: amqp091-go: Denial of Service via oversized AMQP payloads github.com/rabbitmq/amqp091-go: amqp091-go: Denial of Service via excessive memory allocation during frame parsing