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The amqp091-go library contains a critical state-boundary flaw where pre-negotiation frame-size mitigation can be bypassed during connection setup.
Specifically, a malicious or compromised AMQP peer can send a crafted seven-byte body-frame header containing an extreme attacker-controlled uint32 payload length.
The client runtime allocates a massive slice matching this declared size before verifying existence or rejecting invalid protocol states.
This security bypass happens because Connection.maxFrameSize starts at a zero value.
The internal reader interprets zero as simultaneously meaning negotiated unlimited and not negotiated yet.
Consequently, the pre-allocation size check is completely bypassed in either case.
The Open function starts the background reader goroutine prior to negotiation and fails to store any limit until connection.tune is processed.
This vulnerability remains fully reachable even when callers explicitly configure Config{FrameSize: frameMinSize}.
A malicious broker exploits this by forcing excessive memory allocation before authentication or connection setup finishes.
On 64-bit systems, a single 7-byte header can request an allocation approaching 4 GiB.
The attacker does not need to transmit the actual body data for the memory exhaustion to trigger.
This leads directly to severe memory pressure, out-of-memory conditions, and process termination.
The root cause involves treating uninitialized connection states identically to unlimited negotiation settings.
Safe reproduction requires verifying that transport payload reads receive the exact malicious slice size.
Differential test harnesses confirm that the zero pre-negotiation state reaches attacker-sized allocations.
In contrast, properly enforced limits correctly reject oversized declarations before buffer allocation occurs.
Protocol specifications require accepting minimum frame sizes only after negotiation, not arbitrary pre-negotiation extremes.
Suggested remediations involve separating pre-negotiation, negotiated finite, and negotiated unlimited states explicitly.
Provisional bounds must initialize before starting reader goroutines and be replaced after connection.tune.
Proper protocol-state checks add vital defense-in-depth against malicious peer manipulations.
This prevents denial of service against resource-constrained client environments.
DailyCVE Form:
Platform: Rabbitmq Go
Version: Below 1.13.0
Vulnerability: Mitigation bypass
Severity: High
date: August 2026
Prediction: Version 1.13.0
What Undercode Say:
To reproduce and validate this pre-negotiation frame limit bypass behavior safely without hitting live services, execute the differential test suite using the following command in the repository root:
go test -run '^TestPreNegotiationFrameLimitBypass$' -count=1 -v ./...
The accompanying safe reproduction code structure used in the test harness:
package amqp091
import (
"encoding/binary"
"io"
"sync"
"testing"
"time"
)
const declaredBodySize = 2 << 20
type stagedFrameConn struct {
mu sync.Mutex
header []byte
headerRead bool
bodyRead chan int
bodyOnce sync.Once
release chan struct{}
releaseOnce sync.Once
}
func newStagedFrameConn() stagedFrameConn {
header := make([]byte, 7)
header[bash] = frameBody
binary.BigEndian.PutUint16(header[1:3], 1)
binary.BigEndian.PutUint32(header[3:7], declaredBodySize)
return &stagedFrameConn{
header: header,
bodyRead: make(chan int, 1),
release: make(chan struct{}),
}
}
func (c stagedFrameConn) Read(p []byte) (int, error) {
c.mu.Lock()
if !c.headerRead {
c.headerRead = true
n := copy(p, c.header)
c.mu.Unlock()
return n, nil
}
c.mu.Unlock()
c.bodyOnce.Do(func() { c.bodyRead <- len(p) })
<-c.release
return 0, io.EOF
}
func (c stagedFrameConn) Write(p []byte) (int, error) { return len(p), nil }
func (c stagedFrameConn) Close() error {
c.releaseOnce.Do(func() { close(c.release) })
return nil
}
Exploit: (Educational Purposes!)
A malicious AMQP broker initiates connection establishment by establishing a transport socket with the client.
Before connection.tune or negotiation completes, the broker sends a crafted 7-byte body frame header where the 32-bit uint payload length is set to an extremely high value (approaching 4 GiB).
Because the client’s maxFrameSize is uninitialized (stored as zero), the parser skips pre-allocation bounds checks.
The client executes an immediate memory allocation (make([]byte, size)) for the declared payload before checking protocol states or reading actual body bytes.
This causes instantaneous memory pressure, exhausting available RAM or triggering container out-of-memory killers to terminate the client application.
Protection:
Update the amqp091-go library to version 1.13.0 or later where the provisional pre-negotiation bounds are properly enforced.
Ensure that provisional frame limits are initialized prior to launching reader goroutines.
Verify that connection state checks explicitly reject body frames before connection setup and tune complete.
Implement robust validation on all untrusted frame headers to prevent uncontrolled memory allocation.
Impact:
A compromised or malicious broker can cause unauthenticated application-layer denial of service.
Clients experience severe memory pressure, out-of-memory crashes, and process termination.
Service availability for dependent applications and microservices is disrupted entirely without requiring credentials or user interaction.
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Sources:
Reported By: github.com
Extra Source Hub:
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