Toxic combinations: when small signals add up to a security incident
At 3 AM, a single IP requested a login page. Harmless. But then, across several hosts and paths, the same source began appending ?debug=true — the sign of an attacker probing the environment to assess the technology stack and plan a breach.
Minor misconfigurations, overlooked firewall events, or request anomalies feel harmless on their own. But when these small signals converge, they can explode into security incidents known as “toxic combinations.” These are exploits where an attacker discovers and compounds many minor issues — such as a debug flag left on a web application or an unauthenticated application path — to breach systems or exfiltrate data.
Cloudflare’s network observes requests to your stack, and as a result, has the data to identify these toxic combinations as they form. In this post, we’ll show you how we surface these signals from our application security data. We’ll go over the most common types of toxic combinations and the dangerous vulnerabilities they present. We will also provide details on how you can use this intelligence to identify and address weaknesses in your stack.
You could define a "toxic combination" in a few different ways, but here Continue reading
ASPA: making Internet routing more secure
Internet traffic relies on the Border Gateway Protocol (BGP) to find its way between networks. However, this traffic can sometimes be misdirected due to configuration errors or malicious actions. When traffic is routed through networks it was not intended to pass through, it is known as a route leak. We have written on our blog multiple times about BGP route leaks and the impact they have on Internet routing, and a few times we have even alluded to a future of path verification in BGP.
While the network community has made significant progress in verifying the final destination of Internet traffic, securing the actual path it takes to get there remains a key challenge for maintaining a reliable Internet. To address this, the industry is adopting a new cryptographic standard called ASPA (Autonomous System Provider Authorization), which is designed to validate the entire path of network traffic and prevent route leaks.
To help the community track the rollout of this standard, Cloudflare Radar has introduced a new ASPA deployment monitoring feature. This view allows users to observe ASPA adoption trends over time across the five Regional Internet Registries (RIRs), and view ASPA records and changes over time Continue reading
Bringing more transparency to post-quantum usage, encrypted messaging, and routing security
Cloudflare Radar already offers a wide array of security insights — from application and network layer attacks, to malicious email messages, to digital certificates and Internet routing.
And today we’re introducing even more. We are launching several new security-related data sets and tools on Radar:
We are extending our post-quantum (PQ) monitoring beyond the client side to now include origin-facing connections. We have also released a new tool to help you check any website's post-quantum encryption compatibility.
A new Key Transparency section on Radar provides a public dashboard showing the real-time verification status of Key Transparency Logs for end-to-end encrypted messaging services like WhatsApp, showing when each log was last signed and verified by Cloudflare's Auditor. The page serves as a transparent interface where anyone can monitor the integrity of public key distribution and access the API to independently validate our Auditor’s proofs.
Routing Security insights continue to expand with the addition of global, country, and network-level information about the deployment of ASPA, an emerging standard that can help detect and prevent BGP route leaks.
Since April 2024, we have tracked the aggregate growth of client support for post-quantum encryption on Cloudflare Continue reading
The most-seen UI on the Internet? Redesigning Turnstile and Challenge Pages
You've seen it. Maybe you didn't register it consciously, but you've seen it. That little widget asking you to verify you're human. That full-page security check before accessing a website. If you've spent any time on the Internet, you've encountered Cloudflare's Turnstile widget or Challenge Pages — likely more times than you can count.
The Turnstile widget – a familiar sight across millions of websites
When we say that a large portion of the Internet sits behind Cloudflare, we mean it. Our Turnstile widget and Challenge Pages are served 7.67 billion times every single day. That's not a typo. Billions. This might just be the most-seen user interface on the Internet.
And that comes with enormous responsibility.
Designing a product with billions of eyeballs on it isn't just challenging — it requires a fundamentally different approach. Every pixel, every word, every interaction has to work for someone's grandmother in rural Japan, a teenager in São Paulo, a visually impaired developer in Berlin, and a busy executive in Lagos. All at the same time. In moments of frustration.
Today we’re sharing the story of how we redesigned Turnstile and Challenge Pages. It's a story told in three parts, by three Continue reading
We deserve a better streams API for JavaScript
Handling data in streams is fundamental to how we build applications. To make streaming work everywhere, the WHATWG Streams Standard (informally known as "Web streams") was designed to establish a common API to work across browsers and servers. It shipped in browsers, was adopted by Cloudflare Workers, Node.js, Deno, and Bun, and became the foundation for APIs like fetch(). It's a significant undertaking, and the people who designed it were solving hard problems with the constraints and tools they had at the time.
But after years of building on Web streams — implementing them in both Node.js and Cloudflare Workers, debugging production issues for customers and runtimes, and helping developers work through far too many common pitfalls — I've come to believe that the standard API has fundamental usability and performance issues that cannot be fixed easily with incremental improvements alone. The problems aren't bugs; they're consequences of design decisions that may have made sense a decade ago, but don't align with how JavaScript developers write code today.
This post explores some of the fundamental issues I see with Web streams and presents an alternative approach built around JavaScript language primitives that demonstrate something better is possible.
How we rebuilt Next.js with AI in one week
*This post was updated at 12:35 pm PT to fix a typo in the build time benchmarks.
Last week, one engineer and an AI model rebuilt the most popular front-end framework from scratch. The result, vinext (pronounced "vee-next"), is a drop-in replacement for Next.js, built on Vite, that deploys to Cloudflare Workers with a single command. In early benchmarks, it builds production apps up to 4x faster and produces client bundles up to 57% smaller. And we already have customers running it in production.
The whole thing cost about $1,100 in tokens.
Next.js is the most popular React framework. Millions of developers use it. It powers a huge chunk of the production web, and for good reason. The developer experience is top-notch.
But Next.js has a deployment problem when used in the broader serverless ecosystem. The tooling is entirely bespoke: Next.js has invested heavily in Turbopack but if you want to deploy it to Cloudflare, Netlify, or AWS Lambda, you have to take that build output and reshape it into something the target platform can actually run.
If you’re thinking: “Isn’t that what OpenNext does?”, you are correct. Continue reading
Cloudflare One is the first SASE offering modern post-quantum encryption across the full platform
During Security Week 2025, we launched the industry’s first cloud-native post-quantum Secure Web Gateway (SWG) and Zero Trust solution, a major step towards securing enterprise network traffic sent from end user devices to public and private networks.
But this is only part of the equation. To truly secure the future of enterprise networking, you need a complete Secure Access Service Edge (SASE).
Today, we complete the equation: Cloudflare One is the first SASE platform to support modern standards-compliant post-quantum (PQ) encryption in our Secure Web Gateway, and across Zero Trust and Wide Area Network (WAN) use cases. More specifically, Cloudflare One now offers post-quantum hybrid ML-KEM (Module-Lattice-based Key-Encapsulation Mechanism) across all major on-ramps and off-ramps.
To complete the equation, we added support for post-quantum encryption to our Cloudflare IPsec (our cloud-native WAN-as-a-Service) and Cloudflare One Appliance (our physical or virtual WAN appliance that establish Cloudflare IPsec connections). Cloudflare IPsec uses the IPsec protocol to establish encrypted tunnels from a customer’s network to Cloudflare’s global network, while IP Anycast is used to automatically route that tunnel to the nearest Cloudflare data center. Cloudflare IPsec simplifies configuration and provides high availability; if a specific data center becomes unavailable, traffic Continue reading
Cloudflare outage on February 20, 2026
On February 20, 2026, at 17:48 UTC, Cloudflare experienced a service outage when a subset of customers who use Cloudflare’s Bring Your Own IP (BYOIP) service saw their routes to the Internet withdrawn via Border Gateway Protocol (BGP).
The issue was not caused, directly or indirectly, by a cyberattack or malicious activity of any kind. This issue was caused by a change that Cloudflare made to how our network manages IP addresses onboarded through the BYOIP pipeline. This change caused Cloudflare to unintentionally withdraw customer prefixes.
For some BYOIP customers, this resulted in their services and applications being unreachable from the Internet, causing timeouts and failures to connect across their Cloudflare deployments that used BYOIP. The website for Cloudflare’s recursive DNS resolver (1.1.1.1) saw 403 errors as well. The total duration of the incident was 6 hours and 7 minutes with most of that time spent restoring prefix configurations to their state prior to the change.
Cloudflare engineers reverted the change and prefixes stopped being withdrawn when we began to observe failures. However, before engineers were able to revert the change, ~1,100 BYOIP prefixes were withdrawn from the Cloudflare network. Some customers were able to restore their Continue reading
Code Mode: give agents an entire API in 1,000 tokens
Model Context Protocol (MCP) has become the standard way for AI agents to use external tools. But there is a tension at its core: agents need many tools to do useful work, yet every tool added fills the model's context window, leaving less room for the actual task.
Code Mode is a technique we first introduced for reducing context window usage during agent tool use. Instead of describing every operation as a separate tool, let the model write code against a typed SDK and execute the code safely in a Dynamic Worker Loader. The code acts as a compact plan. The model can explore tool operations, compose multiple calls, and return just the data it needs. Anthropic independently explored the same pattern in their Code Execution with MCP post.
Today we are introducing a new MCP server for the entire Cloudflare API — from DNS and Zero Trust to Workers and R2 — that uses Code Mode. With just two tools, search() and execute(), the server is able to provide access to the entire Cloudflare API over MCP, while consuming only around 1,000 tokens. The footprint stays fixed, no matter how many API endpoints exist.
For a large API like Continue reading
Shedding old code with ecdysis: graceful restarts for Rust services at Cloudflare
ecdysis | ˈekdəsəs |
noun
the process of shedding the old skin (in reptiles) or casting off the outer cuticle (in insects and other arthropods).
How do you upgrade a network service, handling millions of requests per second around the globe, without disrupting even a single connection?
One of our solutions at Cloudflare to this massive challenge has long been ecdysis, a Rust library that implements graceful process restarts where no live connections are dropped, and no new connections are refused.
Last month, we open-sourced ecdysis, so now anyone can use it. After five years of production use at Cloudflare, ecdysis has proven itself by enabling zero-downtime upgrades across our critical Rust infrastructure, saving millions of requests with every restart across Cloudflare’s global network.
It’s hard to overstate the importance of getting these upgrades right, especially at the scale of Cloudflare’s network. Many of our services perform critical tasks such as traffic routing, TLS lifecycle management, or firewall rules enforcement, and must operate continuously. If one of these services goes down, even for an instant, the cascading impact can be catastrophic. Dropped connections and failed requests quickly lead to degraded customer performance and business impact.
When Continue reading
Introducing Markdown for Agents
The way content and businesses are discovered online is changing rapidly. In the past, traffic originated from traditional search engines, and SEO determined who got found first. Now the traffic is increasingly coming from AI crawlers and agents that demand structured data within the often-unstructured Web that was built for humans.
As a business, to continue to stay ahead, now is the time to consider not just human visitors, or traditional wisdom for SEO-optimization, but start to treat agents as first-class citizens.
Feeding raw HTML to an AI is like paying by the word to read packaging instead of the letter inside. A simple ## About Us on a page in markdown costs roughly 3 tokens; its HTML equivalent – <h2 class="section-title" id="about">About Us</h2> – burns 12-15, and that's before you account for the <div> wrappers, nav bars, and script tags that pad every real web page and have zero semantic value.
This blog post you’re reading takes 16,180 tokens in HTML and 3,150 tokens when converted to markdown. That’s a 80% reduction in token usage.
Markdown has quickly become the lingua franca for agents and AI systems as a whole. The format’s explicit structure Continue reading
2025 Q4 DDoS threat report: A record-setting 31.4 Tbps attack caps a year of massive DDoS assaults
Welcome to the 24th edition of Cloudflare’s Quarterly DDoS Threat Report. In this report, Cloudforce One offers a comprehensive analysis of the evolving threat landscape of Distributed Denial of Service (DDoS) attacks based on data from the Cloudflare network. In this edition, we focus on the fourth quarter of 2025, as well as share overall 2025 data.
The fourth quarter of 2025 was characterized by an unprecedented bombardment launched by the Aisuru-Kimwolf botnet, dubbed “The Night Before Christmas" DDoS attack campaign. The campaign targeted Cloudflare customers as well as Cloudflare’s dashboard and infrastructure with hyper-volumetric HTTP DDoS attacks exceeding rates of 200 million requests per second (rps), just weeks after a record-breaking 31.4 Terabits per second (Tbps) attack.
DDoS attacks surged by 121% in 2025, reaching an average of 5,376 attacks automatically mitigated every hour.
In the final quarter of 2025, Hong Kong jumped 12 places, making it the second most DDoS’d place on earth. The United Kingdom also leapt by an astonishing 36 places, making it the sixth most-attacked place.
Infected Android TVs — part of the Aisuru-Kimwolf botnet — bombarded Cloudflare’s network with hyper-volumetric HTTP DDoS attacks, while Telcos emerged as the most-attacked industry.
Improve global upload performance with R2 Local Uploads
Today, we are launching Local Uploads for R2 in open beta. With Local Uploads enabled, object data is automatically written to a storage location close to the client first, then asynchronously copied to where the bucket lives. The data is immediately accessible and stays strongly consistent. Uploads get faster, and data feels global.
For many applications, performance needs to be global. Users uploading media content from different regions, for example, or devices sending logs and telemetry from all around the world. But your data has to live somewhere, and that means uploads from far away have to travel the full distance to reach your bucket.
R2 is object storage built on Cloudflare's global network. Out of the box, it automatically caches object data globally for fast reads anywhere — all while retaining strong consistency and zero egress fees. This happens behind the scenes whether you're using the S3 API, Workers Bindings, or plain HTTP. And now with Local Uploads, both reads and writes can be fast from anywhere in the world.
Try it yourself in this demo to see the benefits of Local Uploads.
Ready to try it? Enable Local Uploads in the Cloudflare Dashboard under your bucket's settings, or Continue reading
Google’s AI advantage: why crawler separation is the only path to a fair Internet
Earlier this week, the UK’s Competition and Markets Authority (CMA) opened its consultation on a package of proposed conduct requirements for Google. The consultation invites comments on the proposed requirements before the CMA imposes any final measures. These new rules aim to address the lack of choice and transparency that publishers (broadly defined as “any party that makes content available on the web”) face over how Google uses search to fuel its generative AI services and features. These are the first consultations on conduct requirements launched under the digital markets competition regime in the UK.
We welcome the CMA’s recognition that publishers need a fairer deal and believe the proposed rules are a step into the right direction. Publishers should be entitled to have access to tools that enable them to control the inclusion of their content in generative AI services, and AI companies should have a level playing field on which to compete.
But we believe the CMA has not gone far enough and should do more to safeguard the UK’s creative sector and foster healthy competition in the market for generative and agentic AI.
In January Continue reading
Building vertical microfrontends on Cloudflare’s platform
Updated at 6:55 a.m. PT
Today, we’re introducing a new Worker template for Vertical Microfrontends (VMFE). This template allows you to map multiple independent Cloudflare Workers to a single domain, enabling teams to work in complete silos — shipping marketing, docs, and dashboards independently — while presenting a single, seamless application to the user.
Most microfrontend architectures are "horizontal", meaning different parts of a single page are fetched from different services. Vertical microfrontends take a different approach by splitting the application by URL path. In this model, a team owning the `/blog` path doesn't just own a component; they own the entire vertical stack for that route – framework, library choice, CI/CD and more. Owning the entire stack of a path, or set of paths, allows teams to have true ownership of their work and ship with confidence.
Teams face problems as they grow, where different frameworks serve varying use cases. A marketing website could be better utilized with Astro, for example, while a dashboard might be better with React. Or say you have a monolithic code base where many teams ship as a collective. An update to add new features from several teams can get frustratingly rolled back because Continue reading
Introducing Moltworker: a self-hosted personal AI agent, minus the minis
The Internet woke up this week to a flood of people buying Mac minis to run Moltbot (formerly Clawdbot), an open-source, self-hosted AI agent designed to act as a personal assistant. Moltbot runs in the background on a user's own hardware, has a sizable and growing list of integrations for chat applications, AI models, and other popular tools, and can be controlled remotely. Moltbot can help you with your finances, social media, organize your day — all through your favorite messaging app.
But what if you don’t want to buy new dedicated hardware? And what if you could still run your Moltbot efficiently and securely online? Meet Moltworker, a middleware Worker and adapted scripts that allows running Moltbot on Cloudflare's Sandbox SDK and our Developer Platform APIs.
Firstly, Cloudflare Workers has never been so compatible with Node.js. Where in the past we had to mock APIs to get some packages running, now those APIs are supported natively by the Workers Runtime.
This has changed how we can build tools on Cloudflare Workers. When we first implemented Playwright, a popular framework for web testing and automation that runs Continue reading
Building a serverless, post-quantum Matrix homeserver
* This post was updated at 11:45 a.m. Pacific time to clarify that the use case described here is a proof of concept and a personal project. Some sections have been updated for clarity.
Matrix is the gold standard for decentralized, end-to-end encrypted communication. It powers government messaging systems, open-source communities, and privacy-focused organizations worldwide.
For the individual developer, however, the appeal is often closer to home: bridging fragmented chat networks (like Discord and Slack) into a single inbox, or simply ensuring your conversation history lives on infrastructure you control. Functionally, Matrix operates as a decentralized, eventually consistent state machine. Instead of a central server pushing updates, homeservers exchange signed JSON events over HTTP, using a conflict resolution algorithm to merge these streams into a unified view of the room's history.
But there is a "tax" to running it. Traditionally, operating a Matrix homeserver has meant accepting a heavy operational burden. You have to provision virtual private servers (VPS), tune PostgreSQL for heavy write loads, manage Redis for caching, configure reverse proxies, and handle rotation for TLS certificates. It’s a stateful, heavy beast that demands to be fed time and money, whether you’re using it a lot Continue reading
Cable cuts, storms, and DNS: a look at Internet disruptions in Q4 2025
In 2025, we observed over 180 Internet disruptions spurred by a variety of causes – some were brief and partial, while others were complete outages lasting for days. In the fourth quarter, we tracked only a single government-directed Internet shutdown, but multiple cable cuts wreaked havoc on connectivity in several countries. Power outages and extreme weather disrupted Internet services in multiple places, and the ongoing conflict in Ukraine impacted connectivity there as well. As always, a number of the disruptions we observed were due to technical problems – with some acknowledged by the relevant providers, while others had unknown causes. In addition, incidents at several hyperscaler cloud platforms and Cloudflare impacted the availability of websites and applications.
This post is intended as a summary overview of observed and confirmed disruptions and is not an exhaustive or complete list of issues that have occurred during the quarter. These anomalies are detected through significant deviations from expected traffic patterns observed across our network. Check out the Cloudflare Radar Outage Center for a full list of verified anomalies and confirmed outages.
The Internet was shut down in Tanzania on October 29 as violent protests took place during the country’s Continue reading
Route leak incident on January 22, 2026
On January 22, 2026, an automated routing policy configuration error caused us to leak some Border Gateway Protocol (BGP) prefixes unintentionally from a router at our data center in Miami, Florida. While the route leak caused some impact to Cloudflare customers, multiple external parties were also affected because their traffic was accidentally funnelled through our Miami data center location.
The route leak lasted 25 minutes, causing congestion on some of our backbone infrastructure in Miami, elevated loss for some Cloudflare customer traffic, and higher latency for traffic across these links. Additionally, some traffic was discarded by firewall filters on our routers that are designed to only accept traffic for Cloudflare services and our customers.
While we’ve written about route leaks before, we rarely find ourselves causing them. This route leak was the result of an accidental misconfiguration on a router in Cloudflare’s network, and only affected IPv6 traffic. We sincerely apologize to the users, customers, and networks we impacted yesterday as a result of this BGP route leak.
We have written multiple times about BGP route leaks, and we even record route leak events on Cloudflare Radar for anyone to view and learn from. To get Continue reading
How we mitigated a vulnerability in Cloudflare’s ACME validation logic
On October 13, 2025, security researchers from FearsOff identified and reported a vulnerability in Cloudflare's ACME (Automatic Certificate Management Environment) validation logic that disabled some of the WAF features on specific ACME-related paths. The vulnerability was reported and validated through Cloudflare’s bug bounty program.
The vulnerability was rooted in how our edge network processed requests destined for the ACME HTTP-01 challenge path (/.well-known/acme-challenge/*).
Here, we’ll briefly explain how this protocol works and the action we took to address the vulnerability.
Cloudflare has patched this vulnerability and there is no action necessary for Cloudflare customers. We are not aware of any malicious actor abusing this vulnerability.
ACME is a protocol used to automate the issuance, renewal, and revocation of SSL/TLS certificates. When an HTTP-01 challenge is used to validate domain ownership, a Certificate Authority (CA) will expect to find a validation token at the HTTP path following the format of http://{customer domain}/.well-known/acme-challenge/{token value}.
If this challenge is used by a certificate order managed by Cloudflare, then Cloudflare will respond on this path and provide the token provided by the CA to the caller. If the token provided does not Continue reading