Data loss prevention
- On this page

Data loss prevention

Protect sensitive data to prevent data loss, and send alerts to a webhooks server in the event of a data breach.

Last updated Apr 23, 2026 If you want to get started quickly, click on the button below.

This creates a repository in your GitHub account and deploys the application to Cloudflare Workers.

export default {
    async fetch(request) {
        const DEBUG = true;
        const SOME_HOOK_SERVER = "https://webhook.flow-wolf.io/hook";

        /**
         * Alert a data breach by posting to a webhook server
         */
        async function postDataBreach(request) {
            return await fetch(SOME_HOOK_SERVER, {
                method: "POST",
                headers: {
                    "content-type": "application/json;charset=UTF-8",
                },
                body: JSON.stringify({
                    ip: request.headers.get("cf-connecting-ip"),
                    time: Date.now(),
                    request: request,
                }),
            });
        }

        /**
         * Define personal data with regular expressions.
         * Respond with block if credit card data, and strip
         * emails and phone numbers from the response.
         * Execution will be limited to MIME type "text/*".
         */
        const response = await fetch(request);

        // Return origin response, if response wasn’t text
        const contentType = response.headers.get("content-type") || "";
        if (!contentType.toLowerCase().includes("text/")) {
            return response;
        }

        let text = await response.text();

        // When debugging replace the response
        // from the origin with an email
        text = DEBUG
            ? text.replace("You may use this", "me@example.com may use this")
            : text;
        const sensitiveRegexsMap = {
            creditCard: String.raw`\b(?:4[0-9]{12}(?:[0-9]{3})?|(?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|6(?:011|5[0-9]{2})[0-9]{12}|(?:2131|1800|35\d{3})\d{11})\b`,
            email: String.raw`\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b`,
            phone: String.raw`\b07\d{9}\b`,
        };

        for (const kind in sensitiveRegexsMap) {
            const sensitiveRegex = new RegExp(sensitiveRegexsMap[kind], "ig");
            const match = await sensitiveRegex.test(text);
            if (match) {
                // Alert a data breach
                await postDataBreach(request);
                // Respond with a block if credit card,
                // otherwise replace sensitive text with `*`s
                return kind === "creditCard"
                    ? new Response(kind + " found\nForbidden\n", {
                            status: 403,
                            statusText: "Forbidden",
                        })
                    : new Response(text.replace(sensitiveRegex, "**********"), response);
            }
        }
        return new Response(text, response);
    },
};

export default {
    async fetch(request): Promise<Response> {
        const DEBUG = true;
        const SOME_HOOK_SERVER = "https://webhook.flow-wolf.io/hook";

        /**
         * Alert a data breach by posting to a webhook server
         */
        async function postDataBreach(request) {
            return await fetch(SOME_HOOK_SERVER, {
                method: "POST",
                headers: {
                    "content-type": "application/json;charset=UTF-8",
                },
                body: JSON.stringify({
                    ip: request.headers.get("cf-connecting-ip"),
                    time: Date.now(),
                    request: request,
                }),
            });
        }

        /**
         * Define personal data with regular expressions.
         * Respond with block if credit card data, and strip
         * emails and phone numbers from the response.
         * Execution will be limited to MIME type "text/*".
         */
        const response = await fetch(request);

        // Return origin response, if response wasn’t text
        const contentType = response.headers.get("content-type") || "";
        if (!contentType.toLowerCase().includes("text/")) {
            return response;
        }

        let text = await response.text();

        // When debugging replace the response
        // from the origin with an email
        text = DEBUG
            ? text.replace("You may use this", "me@example.com may use this")
            : text;
        const sensitiveRegexsMap = {
            creditCard: String.raw`\b(?:4[0-9]{12}(?:[0-9]{3})?|(?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|6(?:011|5[0-9]{2})[0-9]{12}|(?:2131|1800|35\d{3})\d{11})\b`,
            email: String.raw`\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b`,
            phone: String.raw`\b07\d{9}\b`,
        };

        for (const kind in sensitiveRegexsMap) {
            const sensitiveRegex = new RegExp(sensitiveRegexsMap[kind], "ig");
            const match = await sensitiveRegex.test(text);
            if (match) {
                // Alert a data breach
                await postDataBreach(request);
                // Respond with a block if credit card,
                // otherwise replace sensitive text with `*`s
                return kind === "creditCard"
                    ? new Response(kind + " found\nForbidden\n", {
                            status: 403,
                            statusText: "Forbidden",
                        })
                    : new Response(text.replace(sensitiveRegex, "**********"), response);
            }
        }
        return new Response(text, response);
    },
} satisfies ExportedHandler;

import re
from workers import WorkerEntrypoint
from datetime import datetime
from js import Response, fetch, JSON, Headers

# Alert a data breach by posting to a webhook server
async def post_data_breach(request):
    some_hook_server = "https://webhook.flow-wolf.io/hook"
    headers = Headers.new({"content-type": "application/json"}.items())
    body = JSON.stringify({
      "ip": request.headers["cf-connecting-ip"],
      "time": datetime.now(),
      "request": request,
    })
    return await fetch(some_hook_server, method="POST", headers=headers, body=body)

class Default(WorkerEntrypoint):
    async def fetch(self, request):
        debug = True

        # Define personal data with regular expressions.
        # Respond with block if credit card data, and strip
        # emails and phone numbers from the response.
        # Execution will be limited to MIME type "text/*".
        response = await fetch(request)

        # Return origin response, if response wasn’t text
        content_type = response.headers["content-type"] or ""
        if "text" not in content_type:
            return response

        text = await response.text()
        # When debugging replace the response from the origin with an email
        text = text.replace("You may use this", "me@example.com may use this") if debug else text

        sensitive_regex = [
        ("credit_card",
        r'\b(?:4[0-9]{12}(?:[0-9]{3})?|(?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|6(?:011|5[0-9]{2})[0-9]{12}|(?:2131|1800|35\d{3})\d{11})\b'),
        ("email", r'\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b'),
        ("phone", r'\b07\d{9}\b'),
        ]
        for (kind, regex) in sensitive_regex:
            match = re.search(regex, text, flags=re.IGNORECASE)
            if match:
                # Alert a data breach
                await post_data_breach(request)
                # Respond with a block if credit card, otherwise replace sensitive text with `*`s
                card_resp = Response.new(kind + " found\nForbidden\n", status=403,statusText="Forbidden")
                sensitive_resp = Response.new(re.sub(regex, "*"*10, text, flags=re.IGNORECASE), response)
                return card_resp if kind == "credit_card" else  sensitive_resp

        return Response.new(text, response)

import { Hono } from 'hono';

const app = new Hono();

// Configuration
const DEBUG = true;
const SOME_HOOK_SERVER = "https://webhook.flow-wolf.io/hook";

// Define sensitive data patterns
const sensitiveRegexsMap = {
  creditCard: String.raw`\b(?:4[0-9]{12}(?:[0-9]{3})?|(?:5[1-5][0-9]{2}|222[1-9]|22[3-9][0-9]|2[3-6][0-9]{2}|27[01][0-9]|2720)[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|6(?:011|5[0-9]{2})[0-9]{12}|(?:2131|1800|35\d{3})\d{11})\b`,
  email: String.raw`\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b`,
  phone: String.raw`\b07\d{9}\b`,
};

/**
 * Alert a data breach by posting to a webhook server
 */
async function postDataBreach(request: Request) {
  return await fetch(SOME_HOOK_SERVER, {
    method: "POST",
    headers: {
      "content-type": "application/json;charset=UTF-8",
    },
    body: JSON.stringify({
      ip: request.headers.get("cf-connecting-ip"),
      time: Date.now(),
      request: request,
    }),
  });
}

// Main middleware to handle data loss prevention
app.use('*', async (c) => {
  // Fetch the origin response
  const response = await fetch(c.req.raw);

  // Return origin response if response wasn't text
  const contentType = response.headers.get("content-type") || "";
  if (!contentType.toLowerCase().includes("text/")) {
    return response;
  }

  // Get the response text
  let text = await response.text();

  // When debugging, replace the response from the origin with an email
  text = DEBUG
    ? text.replace("You may use this", "me@example.com may use this")
    : text;

  // Check for sensitive data
  for (const kind in sensitiveRegexsMap) {
    const sensitiveRegex = new RegExp(sensitiveRegexsMap[kind], "ig");
    const match = sensitiveRegex.test(text);

    if (match) {
      // Alert a data breach
      await postDataBreach(c.req.raw);

      // Respond with a block if credit card, otherwise replace sensitive text with `*`s
      if (kind === "creditCard") {
        return c.text(`${kind} found\nForbidden\n`, 403);
      } else {
        return new Response(text.replace(sensitiveRegex, "**********"), {
          status: response.status,
          statusText: response.statusText,
          headers: response.headers,
        });
      }
    }
  }

  // Return the modified response
  return new Response(text, {
    status: response.status,
    statusText: response.statusText,
    headers: response.headers,
  });
});

export default app;

Was this helpful?

YesNo

{"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/workers/examples/data-loss-prevention/#page","headline":"Data loss prevention","description":"Protect sensitive data to prevent data loss, and send alerts to a webhooks server in the event of a data breach.","url":"https://developers.cloudflare.com/workers/examples/data-loss-prevention/","inLanguage":"en","image":"https://developers.cloudflare.com/workers/examples/data-loss-prevention/og.png?v=7c8e7c60f802c9b3","dateModified":"2026-04-23","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. Build, secure, and scale without managing infrastructure","url":"https://www.cloudflare.com/","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"],"logo":{"@type":"ImageObject","url":"https://developers.cloudflare.com/logo.svg"},"address":{"@type":"PostalAddress","streetAddress":"101 Townsend St","addressLocality":"San Francisco","addressRegion":"CA","postalCode":"94107","addressCountry":"US"},"contactPoint":[{"@type":"ContactPoint","contactType":"Customer Support","url":"https://support.cloudflare.com/","availableLanguage":["English"]},{"@type":"ContactPoint","contactType":"Sales","url":"https://www.cloudflare.com/contact/","availableLanguage":["English"]}]},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"},"keywords":["Security","JavaScript","TypeScript","Python"]}

description: Send debugging information in an errored response to a logging service. title: Debugging logs image: https://developers.cloudflare.com/workers/examples/debugging-logs/og.png?v=7697cbe356825cf2

Documentation Index
Fetch the complete documentation index at: https://developers.cloudflare.com/workers/llms.txt
Use this file to discover all available pages before exploring further.

Data loss prevention

Data loss prevention

On this page