s3tk

A security toolkit for Amazon S3

🍊 Battle-tested at Instacart

Installation

Run:

pip install s3tk

You can use the AWS CLI or AWS Vault to set up your AWS credentials:

pip install awscli
aws configure

See IAM policies needed for each command.

Commands

Scan

Scan your buckets for:

• ACL open to public
• policy open to public
• public access blocked
• logging enabled
• versioning enabled
• default encryption enabled

s3tk scan

Only run on specific buckets

s3tk scan my-bucket my-bucket-2

Also works with wildcards

s3tk scan "my-bucket*"

Confirm correct log bucket(s) and prefix

s3tk scan --log-bucket my-s3-logs --log-bucket other-region-logs --log-prefix "{bucket}/"

Check CloudTrail object-level logging [experimental]

s3tk scan --object-level-logging

Skip logging, versioning, or default encryption

s3tk scan --skip-logging --skip-versioning --skip-default-encryption

Get email notifications of failures (via SNS)

s3tk scan --sns-topic arn:aws:sns:...

List Policy

List bucket policies

s3tk list-policy

Only run on specific buckets

s3tk list-policy my-bucket my-bucket-2

Show named statements

s3tk list-policy --named

Set Policy

Note: This replaces the previous policy

Only private uploads

s3tk set-policy my-bucket --no-object-acl

Delete Policy

Delete policy

s3tk delete-policy my-bucket

Block Public Access

Block public access on specific buckets

s3tk block-public-access my-bucket my-bucket-2

Use the --dry-run flag to test

Enable Logging

Enable logging on all buckets

s3tk enable-logging --log-bucket my-s3-logs

Only on specific buckets

s3tk enable-logging my-bucket my-bucket-2 --log-bucket my-s3-logs

Set log prefix ({bucket}/ by default)

s3tk enable-logging --log-bucket my-s3-logs --log-prefix "logs/{bucket}/"

Use the --dry-run flag to test

A few notes about logging:

• buckets with logging already enabled are not updated at all
• the log bucket must in the same region as the source bucket - run this command multiple times for different regions
• it can take over an hour for logs to show up

Enable Versioning

Enable versioning on all buckets

s3tk enable-versioning

Only on specific buckets

s3tk enable-versioning my-bucket my-bucket-2

Use the --dry-run flag to test

Enable Default Encryption

Enable default encryption on all buckets

s3tk enable-default-encryption

Only on specific buckets

s3tk enable-default-encryption my-bucket my-bucket-2

This does not encrypt existing objects - use the encrypt command for this

Use the --dry-run flag to test

Scan Object ACL

Scan ACL on all objects in a bucket

s3tk scan-object-acl my-bucket

Only certain objects

s3tk scan-object-acl my-bucket --only "*.pdf"

Except certain objects

s3tk scan-object-acl my-bucket --except "*.jpg"

Reset Object ACL

Reset ACL on all objects in a bucket

s3tk reset-object-acl my-bucket

This makes all objects private. See bucket policies for how to enforce going forward.

Use the --dry-run flag to test

Specify certain objects the same way as scan-object-acl

Encrypt

Encrypt all objects in a bucket with server-side encryption

s3tk encrypt my-bucket

Use S3-managed keys by default. For KMS-managed keys, use:

s3tk encrypt my-bucket --kms-key-id arn:aws:kms:...

For customer-provided keys, use:

s3tk encrypt my-bucket --customer-key secret-key

Use the --dry-run flag to test

Specify certain objects the same way as scan-object-acl

Note: Objects will lose any custom ACL

Delete Unencrypted Versions

Delete all unencrypted versions of objects in a bucket

s3tk delete-unencrypted-versions my-bucket

For safety, this will not delete any current versions of objects

Use the --dry-run flag to test

Specify certain objects the same way as scan-object-acl

Scan DNS

Scan Route 53 for buckets to make sure you own them

s3tk scan-dns

Otherwise, you may be susceptible to subdomain takeover

Credentials

Credentials can be specified in ~/.aws/credentials or with environment variables. See this guide for an explanation of environment variables.

You can specify a profile to use with:

AWS_PROFILE=your-profile s3tk

IAM Policies

Here are the permissions needed for each command. Only include statements you need.

{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "Scan",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:GetBucketAcl",
"s3:GetBucketPolicy",
"s3:GetBucketPublicAccessBlock",
"s3:GetBucketLogging",
"s3:GetBucketVersioning",
"s3:GetEncryptionConfiguration"
],
"Resource": "*"
},
{
"Sid": "ScanObjectLevelLogging",
"Effect": "Allow",
"Action": [
"cloudtrail:ListTrails",
"cloudtrail:GetTrail",
"cloudtrail:GetEventSelectors",
"s3:GetBucketLocation"
],
"Resource": "*"
},
{
"Sid": "ScanDNS",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"route53:ListHostedZones",
"route53:ListResourceRecordSets"
],
"Resource": "*"
},
{
"Sid": "ListPolicy",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:GetBucketPolicy"
],
"Resource": "*"
},
{
"Sid": "SetPolicy",
"Effect": "Allow",
"Action": [
"s3:PutBucketPolicy"
],
"Resource": "*"
},
{
"Sid": "DeletePolicy",
"Effect": "Allow",
"Action": [
"s3:DeleteBucketPolicy"
],
"Resource": "*"
},
{
"Sid": "BlockPublicAccess",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:PutBucketPublicAccessBlock"
],
"Resource": "*"
},
{
"Sid": "EnableLogging",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:PutBucketLogging"
],
"Resource": "*"
},
{
"Sid": "EnableVersioning",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:PutBucketVersioning"
],
"Resource": "*"
},
{
"Sid": "EnableDefaultEncryption",
"Effect": "Allow",
"Action": [
"s3:ListAllMyBuckets",
"s3:PutEncryptionConfiguration"
],
"Resource": "*"
},
{
"Sid": "ResetObjectAcl",
"Effect": "Allow",
"Action": [
"s3:ListBucket",
"s3:GetObjectAcl",
"s3:PutObjectAcl"
],
"Resource": [
"arn:aws:s3:::my-bucket",
"arn:aws:s3:::my-bucket/*"
]
},
{
"Sid": "Encrypt",
"Effect": "Allow",
"Action": [
"s3:ListBucket",
"s3:GetObject",
"s3:PutObject"
],
"Resource": [
"arn:aws:s3:::my-bucket",
"arn:aws:s3:::my-bucket/*"
]
},
{
"Sid": "DeleteUnencryptedVersions",
"Effect": "Allow",
"Action": [
"s3:ListBucketVersions",
"s3:GetObjectVersion",
"s3:DeleteObjectVersion"
],
"Resource": [
"arn:aws:s3:::my-bucket",
"arn:aws:s3:::my-bucket/*"
]
}
]
}

Access Logs

Amazon Athena is great for querying S3 logs. Create a table and query away:

SELECT
parse_datetime(requestdatetime, 'dd/MMM/yyyy:HH:mm:ss Z') AStime,
key,
remoteip,
useragent
FROMs3_access_logs_db.mybucket_logsWHERE
requester ='-'AND httpstatus LIKE'2%'AND key LIKE'some-keys%'ORDER BY1

CloudTrail Logs

Amazon Athena is also great for querying CloudTrail logs. Create a table and query away:

SELECT
eventtime,
eventname,
useridentity.username,
requestparameters
FROM
cloudtrail_logs
WHERE
eventname LIKE'%Bucket%'ORDER BY1

Best Practices

Keep things simple and follow the principle of least privilege to reduce the chance of mistakes.

• Strictly limit who can perform bucket-related operations
• Avoid mixing objects with different permissions in the same bucket (use a bucket policy to enforce this)
• Don’t specify public read permissions on a bucket level (no GetObject in bucket policy)
• Monitor configuration frequently for changes

Bucket Policies

Only private uploads

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Deny",
"Principal": "*",
"Action": "s3:PutObjectAcl",
"Resource": "arn:aws:s3:::my-bucket/*"
}
]
}

Performance

For commands that iterate over bucket objects (scan-object-acl, reset-object-acl, encrypt, and delete-unencrypted-versions), run s3tk on an EC2 server for minimum latency.

Notes

The set-policy, block-public-access, enable-logging, enable-versioning, and enable-default-encryption commands are provided for convenience. We recommend Terraform for managing your buckets.

resource"aws_s3_bucket""my_bucket" {
bucket="my-bucket"acl="private"logging {
target_bucket="my-s3-logs"target_prefix="my-bucket/"
}
versioning {
enabled=true
}
}
resource"aws_s3_bucket_public_access_block""my_bucket" {
bucket="${aws_s3_bucket.my_bucket.id}"block_public_acls=trueblock_public_policy=trueignore_public_acls=truerestrict_public_buckets=true
}

Upgrading

Run:

pip install s3tk --upgrade

To use master, run:

pip install git+https://github.com/ankane/s3tk.git --upgrade

Docker

Run:

docker run -it ankane/s3tk aws configure

Commit your credentials:

docker commit $(docker ps -l -q) my-s3tk

And run:

docker run -it my-s3tk s3tk scan

History

View the changelog

Contributing

Everyone is encouraged to help improve this project. Here are a few ways you can help:

• Report bugs
• Fix bugs and submit pull requests
• Write, clarify, or fix documentation
• Suggest or add new features

To get started with development:

git clone https://github.com/ankane/s3tk.git
cd s3tk
pip install --group dev