gd2slack.template

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "Demonstrates how to connect GuardDuty to your Slack channel. The template Installs a Lambda function that writes CW Events to a Slack incoming web hook. This relies on you creating an *incoming web hook* in your slack account and simply passing the URL as a parameter to this template",
    "Metadata": {
        "AWS::CloudFormation::Interface": {
            "ParameterGroups": [
                {
                    "Label": {
                        "default": "Slack Configuration"
                    },
                    "Parameters": [
                        "IncomingWebHookURL",
                        "SlackChannel",
                        "MinSeverityLevel"
                    ]
                }
            ],
            "ParameterLabels": {
                "IncomingWebHookURL": {
                    "default": "Slack Incoming Web Hook URL"
                },
                "SlackChannel" : {
                    "default" : "Slack channel to send findings to"
                },
                "MinSeverityLevel" : {
                    "default"  : "Minimum severity level (LOW, MEDIUM, HIGH)"
                }
            }
        }
    },
    "Parameters": {
        "IncomingWebHookURL": {
            "Default": "https://hooks.slack.com/services/XXXXXX/YYYYY/REPLACE_WITH_YOURS",
            "Description": "Your unique Incoming Web Hook URL from slack service",
            "Type": "String"
        },
        "SlackChannel": {
            "Default": "#general",
            "Description": "The slack channel to send findings to",
            "Type": "String"
        },
        "MinSeverityLevel": {
            "Default": "LOW",
            "Description": "The minimum findings severity to send to your slack channel (LOW, MEDIUM or HIGH)",
            "Type": "String",
	    "AllowedValues": [
                "LOW",
                "MEDIUM",
                "HIGH"
            ]
        }
    },
    "Resources": {
        "GuardDutyToSlackRole": {
            "Type": "AWS::IAM::Role",
            "Properties": {
                "AssumeRolePolicyDocument": {
                    "Statement": [
                        {
                            "Effect": "Allow",
                            "Principal": {
                                "Service": [
                                    "lambda.amazonaws.com"
                                ]
                            },
                            "Action": [
                                "sts:AssumeRole"
                            ]
                        }
                    ]
                },
                "Path": "/service-role/",
                "ManagedPolicyArns": [
                    "arn:aws:iam::aws:policy/AWSXrayWriteOnlyAccess",
                    "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
                    
                ],
                "Policies": []
            }
        },
        "ScheduledRule": {
	    "DependsOn": "findingsToSlack",
            "Type": "AWS::Events::Rule",
            "Properties": {
                "Description": "GuardDutyRule",
                "State": "ENABLED",
                "EventPattern" : { "source": ["aws.guardduty"], "detail-type": ["GuardDuty Finding"] },
                "Targets": [{
                    "Arn": { "Fn::GetAtt" : ["findingsToSlack", "Arn"] },
                    "Id": "GuardDutyFunction"
                 }]
             }
        },
        "LambdaInvokePermission": {
            "DependsOn": ["findingsToSlack","ScheduledRule"],
            "Type": "AWS::Lambda::Permission",
             "Properties": {
                 "Action": "lambda:InvokeFunction",
                 "Principal": "events.amazonaws.com",
                 "FunctionName": { "Fn::GetAtt" : ["findingsToSlack", "Arn"] },
                 "SourceArn": { "Fn::GetAtt": ["ScheduledRule", "Arn"]}
            }
        },
        "findingsToSlack": {
            "Type": "AWS::Lambda::Function",
            "Properties": {
                "Handler": "index.handler",
                "Role": {"Fn::GetAtt" : ["GuardDutyToSlackRole", "Arn"] },
                "Code": {
                    "ZipFile" : {
                        "Fn::Join": [ "", [
    "'use strict';\n",
    "\n",
    "/**\n",
    " * Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.\n",
    " * SPDX-License-Identifier: MIT-0\n",
    " */\n",
    "const AWS = require('aws-sdk');\n",
    "const url = require('url');\n",
    "const https = require('https');\n",
    "\n",
    "const webHookUrl = process.env['webHookUrl'];\n",
    "const slackChannel = process.env.slackChannel;\n",
    "const minSeverityLevel = process.env['minSeverityLevel'];\n",
    "\n",
    "function postMessage(message, callback) {\n",
    "    const body = JSON.stringify(message);\n",
    "    const options = url.parse(webHookUrl);\n",
    "    options.method = 'POST';\n",
    "    options.headers = {\n",
    "        'Content-Type': 'application/json',\n",
    "        'Content-Length': Buffer.byteLength(body),\n",
    "    };\n",
    "\n",
    "    const postReq = https.request(options, (res) => {\n",
    "        const chunks = [];\n",
    "        res.setEncoding('utf8');\n",
    "        res.on('data', (chunk) => chunks.push(chunk));\n",
    "        res.on('end', () => {\n",
    "            if (callback) {\n",
    "                callback({\n",
    "                    body: chunks.join(''),\n",
    "                    statusCode: res.statusCode,\n",
    "                    statusMessage: res.statusMessage,\n",
    "                });\n",
    "            }\n",
    "        });\n",
    "    return res;\n",
    "    });\n",
    "\n",
    "    postReq.write(body);\n",
    "    postReq.end();\n",
    "}\n",
    "\n",
    "function processEvent(event, callback) {\n",
    "    const message = event;\n",
    "    const consoleUrl = `https://console.aws.amazon.com/guardduty`;\n",
    "    const finding = message.detail.type;\n",
    "    const findingDescription = message.detail.description;\n",	
    "    const findingTime = message.detail.updatedAt;\n",
    "    const findingTimeEpoch = Math.floor(new Date(findingTime) / 1000);\n",
    "    const account =  message.detail.accountId;\n",
    "    const region =  message.region;\n",
    "    const messageId = message.detail.id;\n",
    "    const lastSeen = `<!date^${findingTimeEpoch}^{date} at {time} | ${findingTime}>`;\n",
    "    var color = '#7CD197';\n",    
    "    var severity = '';\n",
    "    var skip = false;\n",
    "\n",    
    "    if (message.detail.severity < 4.0) {\n",
    "        if (minSeverityLevel !== 'LOW') {\n",
    "            skip = true;\n",
    "        }\n",
    "        severity = 'Low';\n",
    "        color = '#e2d43b';\n",
    "    } else if (message.detail.severity < 7.0) {\n",
    "        if (minSeverityLevel !== 'LOW' && minSeverityLevel !== 'MEDIUM') {\n",
    "            skip = true;\n",
    "        }\n",
    "        severity = 'Medium';\n",
    "        color = '#ff8c00';\n",
    "    } else if (message.detail.severity >= 7.0) {\n",
    "        severity = 'High';\n",
    "        color = '#ad0614';\n",
    "    } else {\n",
    "        skip = true;\n",
    "    }\n",
    "\n",
    "    const attachment = [{\n",
    "              \"fallback\": finding + ` - ${consoleUrl}/home?region=` +\n",
    "        `${region}#/findings?search=id%3D${messageId}`,\n",
    "        \"pretext\": `*Finding in ${region} for Acct: ${account}*`,\n",
    "        \"title\": `${finding}`,\n", 
    "        \"title_link\": `${consoleUrl}/home?region=${region}#/findings?search=id%3D${messageId}`,\n",
    "        \"text\": `${findingDescription}`,\n",
    "        \"fields\": [\n",
    "            {\"title\": \"Severity\",\"value\": `${severity}`, \"short\": true},\n",
    "            {\"title\": \"Region\",\"value\": `${region}`,\"short\": true},\n",
    "            {\"title\": \"Last Seen\",\"value\": `${lastSeen}`, \"short\": true}\n",
    "        ],\n", 
    "        \"mrkdwn_in\": [\"pretext\"],\n",
    "        \"color\": color\n",
    "        }];\n",
    "\n",
    "    const slackMessage = {\n",
    "        channel: slackChannel,\n",
    "        text : '',\n",
    "        attachments : attachment,\n",
    "        username: 'GuardDuty',\n",
    "        'mrkdwn': true,\n",
    "        icon_url: 'https://raw.githubusercontent.com/aws-samples/amazon-guardduty-to-slack/master/images/gd_logo.png'\n",
    "    };\n",
    "\n",
    "    if (!skip) {\n",
    "        postMessage(slackMessage, (response) => {\n",
    "            if (response.statusCode < 400) {\n",
    "                console.info('Message posted successfully');\n",
    "                callback(null);\n",
    "            } else if (response.statusCode < 500) {\n",
    "                console.error(`Error posting message to Slack API: ${response.statusCode} - ${response.statusMessage}`);\n",
    "                callback(null);\n",
    "            } else {\n",
    "                callback(`Server error when processing message: ${response.statusCode} - ${response.statusMessage}`);\n",
    "            }\n",
    "        });\n",
    "    }\n",
    "}\n",
    "\n",
    "exports.handler = (event, context, callback) => {\n",
    "        processEvent(event, callback);\n",
    "};\n"]]
                    }},
               "Environment" : {
		    "Variables" : {
			"slackChannel" : { "Ref" : "SlackChannel" },
			"webHookUrl" : { "Ref": "IncomingWebHookURL" },
			"minSeverityLevel" : {"Ref" : "MinSeverityLevel"}
		    }
		},
                "Runtime": "nodejs14.x",
		"MemorySize" : "128",
                "Timeout": "10",
		"Description" : "Lambda to push GuardDuty findings to slack",
                "TracingConfig": {
                    "Mode": "Active"
                }
	    }
	}
    }
}