A Serverless Security Library for Developers. Regain Control Over Your AWS Lambda & Google Cloud Functions Runtimes.

Created & maintained by PureSec

FunctionShield is a 100% free AWS Lambda security and Google Cloud Functions security library that equips developers with the ability to easily enforce strict security controls on serverless runtimes by addressing 4 common use cases:

• Disable outbound internet connectivity (except for AWS/Google Cloud resources) from the serverless runtime environment, if such connections are not required
• Disable read/write on the /tmp/ directory, if such operations are not required
• Disable child process execution, if such execution is not required by the function
• Disable read access to the function's handler and prevent source code leakage

In addition to the security protections provided, developers also gain tremendous security visibility when using FunctionShield, even if it's just set to "alert". With FunctionShield deployed in your functions, you can quickly get an idea of what your function is executing, who it is communicating with, and whether or not it is writing to disk.

There have been numerous cases in recent years where malicious actors created bogus software packages that look authentic, or infected existing open source packages with code that leaks sensitive data such as credentials or environment variables. According to a recent survey of 16,000 developers by NPM inc. - 77% of the respondents were concerned with the security of open source software packages. Some organizations have responded to this threat by isolating sensitive serverless functions inside a Virtual Private Cloud (VPC) and using a NAT gateway to monitor/restrict outbound traffic. However, this VPC-based solution presents its own technical challenges.

• By monitoring (or blocking) outbound network traffic from your function, you can be certain that your data is never leaked
• By disabling read/write operations on the /tmp/ directory, you can make your function truly ephemeral
• By disabling the ability to launch child processes, you can make sure that no rogue processes are spawned without your knowledge by potentially malicious packages
• By disabling the ability to read the function's (handler) source code through the file system, you can prevent handler source code leakage, which is oftentimes the first step in a serverless attack

FunctionShield uses a proprietary behavioral-based runtime protection engine, which enforces the behavior that you define. FunctionShield lives in and around the serverless language runtime. All you have to do is import the library into your code. No function wrapping required. FunctionShield doesn't wrap your code, or perform any kind of monkey-patching.

Below is a sample code snippet, demonstrating how to use FunctionShield:

var AWS = require('aws-sdk');
const FunctionShield = require('@puresec/function-shield');
FunctionShield.configure({
    policy: {
        // 'block' mode => active blocking
        // 'alert' mode => log only
        // 'allow' mode => allowed, implicitly occurs if key does not exist
        outbound_connectivity: "block",
        read_write_tmp: "block", 
        create_child_process: "block",
        read_handler: "block" },
    token: process.env.FUNCTION_SHIELD_TOKEN });

exports.hello = async (event) => {
    // ... // your code
};

import boto3
import function_shield

function_shield.configure({
    "policy": {
        # 'block' mode => active blocking
        # 'alert' mode => log only
        # 'allow' mode => allowed, implicitly occurs if key does not exist
        "outbound_connectivity": "block",
        "read_write_tmp": "block",
        "create_child_process": "block",
        "read_handler": "block"
    },
    "token": os.environ['FUNCTION_SHIELD_TOKEN']
})

def handler(event, context):
    # Your Code Here #

package com.serverless;

import java.util.Map;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import org.json.JSONObject;
import io.puresec.FunctionShield;

public class Handler implements RequestHandler <Map <String, Object> , String >
{
    static
    {
        /* 'block' mode => active blocking */
        /* 'alert' mode => log only */
        /* 'allow' mode => allowed, implicitly occurs if key does not exist */
        FunctionShield.configure(new JSONObject()
            .put("policy", new JSONObject()
                .put("read_write_tmp", "alert")
                .put("create_child_process", "alert")
                .put("outbound_connectivity", "block")
                .put("read_handler", "block"))
            .put("token", System.getenv("FUNCTION_SHIELD_TOKEN")));
    }

    @Override
    public String handleRequest(Map <String, Object> input, Context context)
    {
        /* TODO: Your function code here */
        return("Done!");
    }

}

'use strict';
const FunctionShield = require('@puresec/function-shield');
FunctionShield.configure(
    {
        policy: {
            // 'block' mode => active blocking
            // 'alert' mode => log only
            // 'allow' mode => allowed, implicitly occurs if key does not exist
            read_write_tmp: "alert",
            create_child_process: "alert",
            outbound_connectivity: "alert",
            read_handler: "alert"
        },
        disable_analytics: false,
        token: process.env.FUNCTION_SHIELD_TOKEN
    });

function handler(request, response) {
    // ... your code ... //
}

import function_shield

function_shield.configure({
    "policy": {
        # 'block' mode => active blocking
        # 'alert' mode => log only
        # 'allow' mode => allowed, implicitly occurs if key does not exist
        "read_write_tmp": "block",
        "create_child_process": "block",
        "outbound_connectivity": "block",
        "read_handler": "block"
    },
    "disable_analytics": False,
    "token": os.environ['FUNCTION_SHIELD_TOKEN']
})


def python37_handler(request):
    # ... your code here ... #

1. Sign up to receive your free FunctionShield token
2. Install the library:
   • Node.js: Run 'npm i @puresec/function-shield'
   • Python: Run 'pip3 install function-shield'
   • Java: See instructions for the Java build tools in this LINK
3. Import the library into your code (see code snippets)
4. Configure your desired security policy
5. Embed the token you received by email into the code
6. Rinse, repeat for all of your functions

At the moment, FunctionShield is offered with the following runtimes support:

• AWS Lambda security: Node.js, Python and Java support
• Google Cloud Functions security: Node.js and Python

FunctionShield is also provided as a middleware for the (MIDDY.JS)[https://github.com/middyjs/middy/blob/master/docs/middlewares.md#functionshield] engine.

• When using the 'outbound-connectivity' restriction, traffic to the cloud enviroment (AWS cloud or Google cloud) resources will still be enabled, in order to avoid disruption to normal function operation
• Logging from FunctionShield is done asynchronously to CloudWatch or Google cloud logs, and does not add latency
• Overall latency of FunctionShield is extremely low, and is expected to be under 1 millisecond.
• Load time for cold-starts was measured around 20ms
• FunctionShield is a completely self-contained technology, no sensitive data is sent to PureSec. Periodically, during cold starts FunctionShield will send information on its configuration and release version. This behavior can be disabled by using the configuration key "disable_analytics: true"
• Alert mode - ('alert') only logs security events. Block mode - ('block') , will halt function execution when a violation of the policy occurs
• You can call the configure() method as many times as needed inside your function. This means that you can temporarily disable or modify FunctionShield's behavior, depending on your needs. For example, in order to allow outbound connectivity only in a certain portion of your code

FunctionShield logs are sent directly to your function's AWS CloudWatch log group or Google cloud logs. Here are a few sample logs, demonstrating the log format you should expect:

// Log example #1:
{
    "function_shield": true,
    "policy": "outbound_connectivity",
    "details": {
        "host": "google.com"
    },
    "mode": "alert"
}

// Log example #2:
{
    "function_shield": true,
    "policy": "read_write_tmp",
    "details": {
        "path": "/tmp/node-alert"
    },
    "mode": "alert"
}

// Log example #3:
{
    "function_shield": true,
    "policy": "create_child_process",
    "details": {
        "path": "/bin/sh"
    },
    "mode": "block"
}

// Log example #4:
{
   "function_shield": true,
   "policy": "read_handler",
   "details": {
       "path": "/var/task/handler.js"
   },
   "mode": "alert"
}

If you want to test FunctionShield, we have prepared some code snippets, which you can use to force triggers:

• Node.js - TEST SNIPPET
• Python - TEST SNIPPET
• Java - TEST SNIPPET

[![FunctionShieldInside](https://www.puresec.io/hubfs/fshield-badge.svg)](https://www.puresec.io/function-shield)

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