CVE-2026-107386

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.

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.

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 describes attacker-controlled, unbounded allocation by a malicious broker and identifies v1.13.0 as the patched version. Pull request 369 added a frame-size check before parser allocation, but the check is active only when the stored maximum is nonzero.

The v1.13.0 source still:

1. starts the reader before protocol negotiation;
2. skips the bound while maxFrameSize == 0;
3. allocates the body using the peer-declared size; and
4. stores the negotiated maximum only after connection.tune.

This appears to be an incomplete-fix or state-boundary bypass of the existing advisory rather than an unrelated allocation issue.

Affected source and root cause

The issue was reproduced at commit 9313fd9ea47bdb4e8f7f5db9bef94d5534d0bdde, dated 2026-07-30. The same relevant control flow is in the v1.13.0 tag.

The vulnerable sequence is:

1. Open starts c.reader(conn) before calling c.open(config).
2. The reader receives a pointer to the initially zero-valued c.maxFrameSize.
3. ReadFrame decodes the peer-controlled uint32 size but rejects it only when max > 0.
4. parseBodyFrame executes make([]byte, size) before io.ReadFull.
5. maxFrameSize is first stored after processing connection.tune.

The source comments and regression tests explicitly combine “negotiated unlimited” with “not yet negotiated” as the same zero state. Those states need different security behavior.

Safe reproduction

This reproducer does not start RabbitMQ, contact any hosted service, send a large payload, or attempt to crash the process. It declares a 2 MiB body and observes the size of the slice passed to the transport's payload Read. Receiving a 2 MiB destination slice proves that the allocation occurred; the test then releases the blocked read and exits.

1. Check out v1.13.0.
2. Save the following as pre_negotiation_frame_limit_test.go in the repository root.
3. Run go test -run '^TestPreNegotiationFrameLimitBypass$' -count=1 -v ..

package amqp091

import (
	"encoding/binary"
	"io"
	"sync"
	"testing"
	"time"
)

const declaredBodySize = 2 << 20

type stagedFrameConn…

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.

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.

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.