bucket-antivirus-function

Scan new objects added to any s3 bucket using AWS Lambda.

Features

• Easy to install
• Send events from an unlimited number of S3 buckets
• Prevent reading of infected files using S3 bucket policies
• Accesses the end-user’s separate installation of open source antivirus engine ClamAV

How It Works

• Each time a new object is added to a bucket, S3 invokes the publisher Lambda function to publish the key name to SQS
• Every minute (adjustable in the infrastructure configuration), the scanner function will run, receiving all messages from the SQS queue
• The scanner function will download (if needed) current antivirus definitions from a S3 bucket. Transfer speeds between a S3 bucket and Lambda are typically faster and more reliable than another source
• The objects are scanned for viruses and malware. Archive files are extracted and the files inside scanned also
• The objects' tags are updated to reflect the result of the scan (malicious or not_malicious), along with the date and time of the scan.

Installation

Build from Source

To build the archive to upload to AWS Lambda, run make all. The build process is completed using the amazonlinux Docker image. The resulting archive will be built at build/lambda.zip. This file will be uploaded to AWS for both Lambda functions below.

Create Relevant AWS Infra via Terragrunt

The infrastructure for this project is built using terragrunt plan and terragrunt apply from the infrastructure directory. infrastructure/modules holds the Terraform that defines the infrastructure configuration.

Adding or Changing Source Buckets

Changing or adding Source Buckets is done by adding bucket names to the av_scan_buckets variable in the terragrunt configuration for the associated environment. Note that currently, only 1 bucket can be targeted by the scanner at a time; this will be fixed in a future release.

Configuration

Runtime configuration is accomplished using environment variables. See the table below for reference.

Variable	Description	Default	Required
AV_DEFINITION_S3_BUCKET	Bucket containing antivirus definition files		Yes
AV_DEFINITION_S3_PREFIX	Prefix for antivirus definition files	clamav_defs	No
AV_DEFINITION_PATH	Path containing files at runtime	/tmp/clamav_defs	No
AV_SCAN_START_SNS_ARN	SNS topic ARN to publish notification about start of scan		No
AV_SCAN_START_METADATA	The tag/metadata indicating the start of the scan	av-scan-start	No
AV_SIGNATURE_METADATA	The tag/metadata name representing file's AV type	av-signature	No
AV_STATUS_CLEAN	The value assigned to clean items inside of tags/metadata	CLEAN	No
AV_STATUS_INFECTED	The value assigned to clean items inside of tags/metadata	INFECTED	No
AV_STATUS_METADATA	The tag/metadata name representing file's AV status	av-status	No
AV_STATUS_SNS_ARN	SNS topic ARN to publish scan results (optional)		No
AV_STATUS_SNS_PUBLISH_CLEAN	Publish AV_STATUS_CLEAN results to AV_STATUS_SNS_ARN	True	No
AV_STATUS_SNS_PUBLISH_INFECTED	Publish AV_STATUS_INFECTED results to AV_STATUS_SNS_ARN	True	No
AV_TIMESTAMP_METADATA	The tag/metadata name representing file's scan time	av-timestamp	No
CLAMAVLIB_PATH	Path to ClamAV library files	./bin	No
CLAMSCAN_PATH	Path to ClamAV clamscan binary	./bin/clamscan	No
FRESHCLAM_PATH	Path to ClamAV freshclam binary	./bin/freshclam	No
DATADOG_API_KEY	API Key for pushing metrics to DataDog (optional)		No
AV_PROCESS_ORIGINAL_VERSION_ONLY	Controls that only original version of an S3 key is processed (if bucket versioning is enabled)	False	No
AV_DELETE_INFECTED_FILES	Controls whether infected files should be automatically deleted	False	No
EVENT_SOURCE	The source of antivirus scan event "S3" or "SNS" (optional)	S3	No
S3_ENDPOINT	The Endpoint to use when interacting wth S3	None	No
SNS_ENDPOINT	The Endpoint to use when interacting wth SNS	None	No
LAMBDA_ENDPOINT	The Endpoint to use when interacting wth Lambda	None	No

S3 Bucket Policy Examples

Deny to download the object if not "not_malicious"

This policy doesn't allow to download the object until:

1. The lambda that run Clam-AV is finished (so the object has a tag)
2. The file is not_malicious

Please make sure to check cloudtrail for the arn:aws:sts, just find the event open it and copy the sts. It should be in the format provided below:

 {
    "Effect": "Deny",
    "NotPrincipal": {
        "AWS": [
            "arn:aws:iam::<<aws-account-number>>:role/<<bucket-antivirus-role>>",
            "arn:aws:sts::<<aws-account-number>>:assumed-role/<<bucket-antivirus-role>>/<<bucket-antivirus-role>>",
            "arn:aws:iam::<<aws-account-number>>:root"
        ]
    },
    "Action": "s3:GetObject",
    "Resource": "arn:aws:s3:::<<bucket-name>>/*",
    "Condition": {
        "StringNotEquals": {
            "s3:ExistingObjectTag/fss-scan-result": "not_malicious"
        }
    }
}

Deny to download and re-tag "malicious" object

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": ["s3:GetObject", "s3:PutObjectTagging"],
      "Principal": "*",
      "Resource": ["arn:aws:s3:::<<bucket-name>>/*"],
      "Condition": {
        "StringEquals": {
          "s3:ExistingObjectTag/fss-scan-result": "malicious"
        }
      }
    }
  ]
}

Manually Scanning Buckets

This has not been refactored since NC adjusted this repo. This does not work currently

You may want to scan all the objects in a bucket that have not previously been scanned or were created prior to setting up your lambda functions. To do this you can use the scan_bucket.py utility.

pip install boto3
scan_bucket.py --lambda-function-name=<lambda_function_name> --s3-bucket-name=<s3-bucket-to-scan>

This tool will scan all objects that have not been previously scanned in the bucket and invoke the lambda function asynchronously. As such you'll have to go to your cloudwatch logs to see the scan results or failures. Additionally, the script uses the same environment variables you'd use in your lambda so you can configure them similarly.

Testing

There are two types of tests in this repository. The first is pre-commit tests and the second are python tests. All of these tests are run by CircleCI.

pre-commit Tests

The pre-commit tests ensure that code submitted to this repository meet the standards of the repository. To get started with these tests run make pre_commit_install. This will install the pre-commit tool and then install it in this repository. Then the github pre-commit hook will run these tests before you commit your code.

To run the tests manually run make pre_commit_tests or pre-commit run -a.

Python Tests

The python tests in this repository use unittest and are run via the nose utility. To run them you will need to install the developer resources and then run the tests:

pip install -r requirements.txt
pip install -r requirements-dev.txt
make test

Local lambdas

You can run the lambdas locally to test out what they are doing without deploying to AWS. This is accomplished by using docker containers that act similarly to lambda. You will need to have set up some local variables in your .envrc.local file and modify them appropriately first before running direnv allow. If you do not have direnv it can be installed with brew install direnv.

For the Scan lambda you will need a test file uploaded to S3 and the variables TEST_BUCKET and TEST_KEY set in your .envrc.local file. Then you can run:

direnv allow
make archive scan

If you want a file that will be recognized as a virus you can download a test file from the EICAR website and uploaded to your bucket.

For the Update lambda you can run:

direnv allow
make archive update

License

Upside Travel, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

ClamAV is released under the GPL Version 2 License and all source for ClamAV is available for download on Github.