CVE-2026-77403: RabbitMQ amqp091-go: Denial of Service via Sub-Spec Frame Size Negotiation

A Denial of Service (DoS) vulnerability exists in the AMQP client’s connection negotiation logic. The AMQP specification explicitly mandates a strict minimum frame size of 4096 bytes to prevent pathological packet fragmentation. While the library defines a frameMinSize = 4096 constant, the connection negotiation loop fails to enforce this boundary, blindly accepting whatever maximum frame size (FrameMax) the server advertises during the handshake.

If a client connects to a malicious or compromised AMQP broker that advertises an extremely low FrameMax (such as 1 byte), the negotiation succeeds. Consequently, every subsequent message transmission is forced to splinter into thousands or millions of single-byte frames, causing massive CPU overhead, thread contention, and a near-instantaneous application freeze.