Defending the Internet: how Cloudflare blocked a monumental 7.3 Tbps DDoS attack
In mid-May 2025, Cloudflare blocked the largest DDoS attack ever recorded: a staggering 7.3 terabits per second (Tbps). This comes shortly after the publication of our DDoS threat report for 2025 Q1 on April 27, 2025, where we highlighted attacks reaching 6.5 Tbps and 4.8 billion packets per second (pps). The 7.3 Tbps attack is 12% larger than our previous record and 1 Tbps greater than a recent attack reported by cyber security reporter Brian Krebs at KrebsOnSecurity.
New world record: 7.3 Tbps DDoS attack autonomously blocked by Cloudflare
The attack targeted a Cloudflare customer, a hosting provider, that uses Magic Transit to defend their IP network. Hosting providers and critical Internet infrastructure have increasingly become targets of DDoS attacks, as we reported in our latest DDoS threat report. Pictured below is an attack campaign from January and February 2025 that blasted over 13.5 million DDoS attacks against Cloudflare’s infrastructure and hosting providers protected by Cloudflare.
DDoS attack campaign target Cloudflare infrastructure and hosting providers protected by Cloudflare
Let's start with some stats, and then we’ll dive into how our systems detected and mitigated this attack.
The 7.3 Tbps attack delivered 37.4 Continue reading
Everything you need to know about NIST’s new guidance in “SP 1800-35: Implementing a Zero Trust Architecture”
For decades, the United States National Institute of Standards and Technology (NIST) has been guiding industry efforts through the many publications in its Computer Security Resource Center. NIST has played an especially important role in the adoption of Zero Trust architecture, through its series of publications that began with NIST SP 800-207: Zero Trust Architecture, released in 2020.
NIST has released another Special Publication in this series, SP 1800-35, titled "Implementing a Zero Trust Architecture (ZTA)" which aims to provide practical steps and best practices for deploying ZTA across various environments. NIST’s publications about ZTA have been extremely influential across the industry, but are often lengthy and highly detailed, so this blog provides a short and easier-to-read summary of NIST’s latest guidance on ZTA.
And so, in this blog post:
We summarize the key items you need to know about this new NIST publication, which presents a reference architecture for Zero Trust Architecture (ZTA) along with a series of “Builds” that demonstrate how different products from various vendors can be combined to construct a ZTA that complies with the reference architecture.
We show how Cloudflare’s Zero Trust product suite can be integrated with offerings from other vendors Continue reading
Cloudflare Log Explorer is now GA, providing native observability and forensics
We are thrilled to announce the General Availability of Cloudflare Log Explorer, a powerful new product designed to bring observability and forensics capabilities directly into your Cloudflare dashboard. Built on the foundation of Cloudflare's vast global network, Log Explorer leverages the unique position of our platform to provide a comprehensive and contextualized view of your environment.
Security teams and developers use Cloudflare to detect and mitigate threats in real-time and to optimize application performance. Over the years, users have asked for additional telemetry with full context to investigate security incidents or troubleshoot application performance issues without having to forward data to third party log analytics and Security Information and Event Management (SIEM) tools. Besides avoidable costs, forwarding data externally comes with other drawbacks such as: complex setups, delayed access to crucial data, and a frustrating lack of context that complicates quick mitigation.
Log Explorer has been previewed by several hundred customers over the last year, and they attest to its benefits:
“Having WAF logs (firewall events) instantly available in Log Explorer with full context — no waiting, no external tools — has completely changed how we manage our firewall rules. I can spot an issue, adjust the Continue reading
Connect any React application to an MCP server in three lines of code
You can deploy a remote Model Context Protocol (MCP) server on Cloudflare in just one-click. Don’t believe us? Click the button below.
This will get you started with a remote MCP server that supports the latest MCP standards and is the reason why thousands of remote MCP servers have been deployed on Cloudflare, including ones from companies like Atlassian, Linear, PayPal, and more.
But deploying servers is only half of the equation — we also wanted to make it just as easy to build and deploy remote MCP clients that can connect to these servers to enable new AI-powered service integrations. That's why we built use-mcp, a React library for connecting to remote MCP servers, and we're excited to contribute it to the MCP ecosystem to enable more developers to build remote MCP clients.
Today, we're open-sourcing two tools that make it easy to build and deploy MCP clients:
use-mcp — A React library that connects to any remote MCP server in just 3 lines of code, with transport, authentication, and session management automatically handled. We're excited to contribute this library to the MCP ecosystem to enable more developers to build remote MCP clients.
Cloudflare service outage June 12, 2025
On June 12, 2025, Cloudflare suffered a significant service outage that affected a large set of our critical services, including Workers KV, WARP, Access, Gateway, Images, Stream, Workers AI, Turnstile and Challenges, AutoRAG, Zaraz, and parts of the Cloudflare Dashboard.
This outage lasted 2 hours and 28 minutes, and globally impacted all Cloudflare customers using the affected services. The cause of this outage was due to a failure in the underlying storage infrastructure used by our Workers KV service, which is a critical dependency for many Cloudflare products and relied upon for configuration, authentication and asset delivery across the affected services. Part of this infrastructure is backed by a third-party cloud provider, which experienced an outage today and directly impacted availability of our KV service.
We’re deeply sorry for this outage: this was a failure on our part, and while the proximate cause (or trigger) for this outage was a third-party vendor failure, we are ultimately responsible for our chosen dependencies and how we choose to architect around them.
This was not the result of an attack or other security event. No data was lost as a result of this incident. Cloudflare Magic Transit and Magic WAN, DNS, cache, proxy, Continue reading
Celebrating 11 years of Project Galileo’s global impact
June 2025 marks the 11th anniversary of Project Galileo, Cloudflare’s initiative to provide free cybersecurity protection to vulnerable organizations working in the public interest around the world. From independent media and human rights groups to community activists, Project Galileo supports those often targeted for their essential work in human rights, civil society, and democracy building.
A lot has changed since we marked the 10th anniversary of Project Galileo. Yet, our commitment remains the same: help ensure that organizations doing critical work in human rights have access to the tools they need to stay online. We believe that organizations, no matter where they are in the world, deserve reliable, accessible protection to continue their important work without disruption.
For our 11th anniversary, we're excited to share several updates including:
An interactive Cloudflare Radar report providing insights into the cyber threats faced by at-risk public interest organizations protected under the project.
An expanded commitment to digital rights in the Asia-Pacific region with two new Project Galileo partners.
New stories from organizations protected by Project Galileo working on the frontlines of civil society, human rights, and journalism from around the world.
Tracking and reporting on cyberattacks with the Project Galileo Continue reading
We shipped FinalizationRegistry in Workers: why you should never use it
We’ve recently added support for the FinalizationRegistry API in Cloudflare Workers. This API allows developers to request a callback when a JavaScript object is garbage-collected, a feature that can be particularly relevant for managing external resources, such as memory allocated by WebAssembly (Wasm). However, despite its availability, our general advice is: avoid using it directly in most scenarios.
Our decision to add FinalizationRegistry — while still cautioning against using it — opens up a bigger conversation: how memory management works when JavaScript and WebAssembly share the same runtime. This is becoming more common in high-performance web apps, and getting it wrong can lead to memory leaks, out-of-memory errors, and performance issues, especially in resource-constrained environments like Cloudflare Workers.
In this post, we’ll look at how JavaScript and Wasm handle memory differently, why that difference matters, and what FinalizationRegistry is actually useful for. We’ll also explain its limitations, particularly around timing and predictability, walk through why we decided to support it, and how we’ve made it safer to use. Finally, we’ll talk about how newer JavaScript language features offer a more reliable and structured approach to solving these problems.
JavaScript relies on automatic memory management through a Continue reading
Building an AI Agent that puts humans in the loop with Knock and Cloudflare’s Agents SDK
This is a guest post by Chris Bell, CTO of Knock
There’s a lot of talk right now about building AI agents, but not a lot out there about what it takes to make those agents truly useful.
An Agent is an autonomous system designed to make decisions and perform actions to achieve a specific goal or set of goals, without human input.
No matter how good your agent is at making decisions, you will need a person to provide guidance or input on the agent’s path towards its goal. After all, an agent that cannot interact or respond to the outside world and the systems that govern it will be limited in the problems it can solve.
That’s where the “human-in-the-loop” interaction pattern comes in. You're bringing a human into the agent's loop and requiring an input from that human before the agent can continue on its task.
In this blog post, we'll use Knock and the Cloudflare Agents SDK to build an AI Agent for a virtual card issuing workflow that requires human approval when a new card is requested.
You can find the complete code for this example in the repository.
Knock is messaging Continue reading
Cloudflare named a Strong Performer in Email Security by Forrester
Today, we are excited to announce that Forrester has recognized Cloudflare Email Security as a Strong Performer and among the top three providers in the ‘current offering’ category in “The Forrester Wave™: Email, Messaging, And Collaboration Security Solutions, Q2 2025” report. Get a complimentary copy of the report here. According to Forrester:
“Cloudflare is a solid choice for organizations looking to augment current email, messaging, and collaboration security tooling with deep content analysis and processing and malware detection capabilities.”
In this evaluation, Forrester analyzed 10 Email Security vendors across 27 different criteria. Cloudflare received the highest scores possible in nine key evaluation criteria, and also scored among the top three in the current offering category. We believe this recognition is due to our ability to deliver stronger security outcomes across email and collaboration tools. These highlights showcase the strength and maturity of our Email Security solution:
Antimalware & sandboxing
Cloudflare’s advanced sandboxing engine analyzes files, whether directly attached or linked via cloud storage, using both static and dynamic analysis. Our AI-powered detectors evaluate attachment structure and behavior in real time, enabling protection not only against known malware but also emerging threats.
Malicious URL detection & web Continue reading
Let’s DO this: detecting Workers Builds errors across 1 million Durable Objects
Cloudflare Workers Builds is our CI/CD product that makes it easy to build and deploy Workers applications every time code is pushed to GitHub or GitLab. What makes Workers Builds special is that projects can be built and deployed with minimal configuration. Just hook up your project and let us take care of the rest!
But what happens when things go wrong, such as failing to install tools or dependencies? What usually happens is that we don’t fix the problem until a customer contacts us about it, at which point many other customers have likely faced the same issue. This can be a frustrating experience for both us and our customers because of the lag time between issues occurring and us fixing them.
We want Workers Builds to be reliable, fast, and easy to use so that developers can focus on building, not dealing with our bugs. That’s why we recently started building an error detection system that can detect, categorize, and surface all build issues occurring on Workers Builds, enabling us to proactively fix issues and add missing features.
It’s also no secret that we’re big fans of being “Customer Zero” at Cloudflare, and Workers Builds is itself a Continue reading
Cloudflare named in 2025 Gartner® Magic Quadrant™ for Security Service Edge
For the third consecutive year, Gartner has named Cloudflare in the Gartner® Magic Quadrant™ for Security Service Edge (SSE) report. This analyst evaluation helps security and network leaders make informed choices about their long-term partners in digital transformation. We are excited to share that Cloudflare is one of only nine vendors recognized in this year’s report. You can read more about our position in the report here.
What’s more exciting is that we’re just getting started. Since 2018, starting with our Zero Trust Network Access (ZTNA) service Cloudflare Access, we’ve continued to push the boundaries of how quickly we can build and deliver a mature SSE platform. In that time, we’ve released multiple products each year, delivering hundreds of features across our platform. That’s not possible without our customers. Today, tens of thousands of customers have chosen to connect and protect their people, devices, applications, networks, and data with Cloudflare. They tell us our platform is faster and easier to deploy and provides a more consistent and reliable user experience, all on a more agile architecture for longer term modernization. We’ve made a commitment to those customers to continue to deliver innovative solutions with the velocity and resilience Continue reading
Resolving a request smuggling vulnerability in Pingora
On April 11, 2025 09:20 UTC, Cloudflare was notified via its Bug Bounty Program of a request smuggling vulnerability in the Pingora OSS framework discovered by a security researcher experimenting to find exploits using Cloudflare’s Content Delivery Network (CDN) free tier which serves some cached assets via Pingora.
Customers using the free tier of Cloudflare’s CDN or users of the caching functionality provided in the open source pingora-proxy and pingora-cache crates could have been exposed. Cloudflare’s investigation revealed no evidence that the vulnerability was being exploited, and was able to mitigate the vulnerability by April 12, 2025 06:44 UTC within 22 hours after being notified.
The bug bounty report detailed that an attacker could potentially exploit an HTTP/1.1 request smuggling vulnerability on Cloudflare’s CDN service. The reporter noted that via this exploit, they were able to cause visitors to Cloudflare sites to make subsequent requests to their own server and observe which URLs the visitor was originally attempting to access.
We treat any potential request smuggling or caching issue with extreme urgency. After our security team escalated the vulnerability, we began investigating immediately, took steps to disable traffic to vulnerable components, and deployed Continue reading
Bringing connections into view: real-time BGP route visibility on Cloudflare Radar
The Internet relies on the Border Gateway Protocol (BGP) to exchange IP address reachability information. This information outlines the path a sender or router can use to reach a specific destination. These paths, conveyed in BGP messages, are sequences of Autonomous System Numbers (ASNs), with each ASN representing an organization that operates its own segment of Internet infrastructure.
Throughout this blog post, we'll use the terms "BGP routes" or simply "routes" to refer to these paths. In essence, BGP functions by enabling autonomous systems to exchange routes to IP address blocks (“IP prefixes”), allowing different entities across the Internet to construct their routing tables.
When network operators debug reachability issues or assess a resource's global reach, BGP routes are often the first thing they examine. Therefore, it’s critical to have an up-to-date view of the routes toward the IP prefixes of interest. Some networks provide tools called "looking glasses" — public routing information services offering data directly from their own BGP routers. These allow external operators to examine routes from that specific network's perspective. Furthermore, services like bgp.tools, bgp.he.net, RouteViews, or the NLNOG RING looking glass offer aggregated, looking glass-like lookup capabilities, drawing Continue reading
Performance measurements… and the people who love them
⚠️ WARNING ⚠️ This blog post contains graphic depictions of probability. Reader discretion is advised.
Measuring performance is tricky. You have to think about accuracy and precision. Are your sampling rates high enough? Could they be too high?? How much metadata does each recording need??? Even after all that, all you have is raw data. Eventually for all this raw performance information to be useful, it has to be aggregated and communicated. Whether it's in the form of a dashboard, customer report, or a paged alert, performance measurements are only useful if someone can see and understand them.
This post is a collection of things I've learned working on customer performance escalations within Cloudflare and analyzing existing tools (both internal and commercial) that we use when evaluating our own performance. A lot of this information also comes from Gil Tene's talk, How NOT to Measure Latency. You should definitely watch that too (but maybe after reading this, so you don't spoil the ending). I was surprised by my own blind spots and which assumptions turned out to be wrong, even though they seemed "obviously true" at the start. I expect I am not alone in these regards. For that Continue reading
Your IPs, your rules: enabling more efficient address space usage
IPv4 addresses have become a costly commodity, driven by their growing scarcity. With the original pool of 4.3 billion addresses long exhausted, organizations must now rely on the secondary market to acquire them. Over the years, prices have surged, often exceeding $30–$50 USD per address, with costs varying based on block size and demand. Given the scarcity, these prices are only going to rise, particularly for businesses that haven’t transitioned to IPv6. This rising cost and limited availability have made efficient IP address management more critical than ever. In response, we’ve evolved how we handle BYOIP (Bring Your Own IP) prefixes to give customers greater flexibility.
Historically, when customers onboarded a BYOIP prefix, they were required to assign it to a single service, binding all IP addresses within that prefix to one service before it was advertised. Once set, the prefix's destination was fixed — to direct traffic exclusively to that service. If a customer wanted to use a different service, they had to onboard a new prefix or go through the cumbersome process of offboarding and re-onboarding the existing one.
As a step towards addressing this limitation, we’ve introduced a new level of flexibility: customers can Continue reading
Vulnerability transparency: strengthening security through responsible disclosure
In an era where digital threats evolve faster than ever, cybersecurity isn't just a back-office concern — it's a critical business priority. At Cloudflare, we understand the responsibility that comes with operating in a connected world. As part of our ongoing commitment to security and transparency, Cloudflare is proud to have joined the United States Cybersecurity and Infrastructure Security Agency’s (CISA) “Secure by Design” pledge in May 2024.
By signing this pledge, Cloudflare joins a growing coalition of companies committed to strengthening the resilience of the digital ecosystem. This isn’t just symbolic — it's a concrete step in aligning with cybersecurity best practices and our commitment to protect our customers, partners, and data.
A central goal in CISA’s Secure by Design pledge is promoting transparency in vulnerability reporting. This initiative underscores the importance of proactive security practices and emphasizes transparency in vulnerability management — values that are deeply embedded in Cloudflare’s Product Security program. We believe that openness around vulnerabilities is foundational to earning and maintaining the trust of our customers, partners, and the broader security community.
Transparency in vulnerability reporting is essential for building trust between companies and customers. In 2008, Continue reading
Forget IPs: using cryptography to verify bot and agent traffic
With the rise of traffic from AI agents, what’s considered a bot is no longer clear-cut. There are some clearly malicious bots, like ones that DoS your site or do credential stuffing, and ones that most site owners do want to interact with their site, like the bot that indexes your site for a search engine, or ones that fetch RSS feeds.
Historically, Cloudflare has relied on two main signals to verify legitimate web crawlers from other types of automated traffic: user agent headers and IP addresses. The User-Agent header allows bot developers to identify themselves, i.e. MyBotCrawler/1.1. However, user agent headers alone are easily spoofed and are therefore insufficient for reliable identification. To address this, user agent checks are often supplemented with IP address validation, the inspection of published IP address ranges to confirm a crawler's authenticity. However, the logic around IP address ranges representing a product or group of users is brittle – connections from the crawling service might be shared by multiple users, such as in the case of privacy proxies and VPNs, and these ranges, often maintained by cloud providers, change over time.
Cloudflare will always try to block malicious bots, but Continue reading
First-party tags in seconds: Cloudflare integrates Google tag gateway for advertisers
If you’re a marketer, advertiser, or a business owner that runs your own website, there’s a good chance you’ve used Google tags in order to collect analytics or measure conversions. A Google tag is a single piece of code you can use across your entire website to send events to multiple destinations like Google Analytics and Google Ads.
Historically, the common way to deploy a Google tag meant serving the JavaScript payload directly from Google’s domain. This can work quite well, but can sometimes impact performance and accurate data measurement. That’s why Google developed a way to deploy a Google tag using your own first-party infrastructure using server-side tagging. However, this server-side tagging required deploying and maintaining a separate server, which comes with a cost and requires maintenance.
That’s why we’re excited to be Google’s launch partner and announce our direct integration of Google tag gateway for advertisers, providing many of the same performance and accuracy benefits of server-side tagging without the overhead of maintaining a separate server.
Any domain proxied through Cloudflare can now serve your Google tags directly from that domain. This allows you to get better measurement signals for your website and can enhance your Continue reading
QUIC restarts, slow problems: udpgrm to the rescue
At Cloudflare, we do everything we can to avoid interruption to our services. We frequently deploy new versions of the code that delivers the services, so we need to be able to restart the server processes to upgrade them without missing a beat. In particular, performing graceful restarts (also known as "zero downtime") for UDP servers has proven to be surprisingly difficult.
We've previously written about graceful restarts in the context of TCP, which is much easier to handle. We didn't have a strong reason to deal with UDP until recently — when protocols like HTTP3/QUIC became critical. This blog post introduces udpgrm, a lightweight daemon that helps us to upgrade UDP servers without dropping a single packet.
Here's the udpgrm GitHub repo.
In the early days of the Internet, UDP was used for stateless request/response communication with protocols like DNS or NTP. Restarts of a server process are not a problem in that context, because it does not have to retain state across multiple requests. However, modern protocols like QUIC, WireGuard, and SIP, as well as online games, use stateful flows. So what happens to the state associated with a flow when a server process is Continue reading
Scaling with safety: Cloudflare’s approach to global service health metrics and software releases
Has your browsing experience ever been disrupted by this error page? Sometimes Cloudflare returns "Error 500" when our servers cannot respond to your web request. This inability to respond could have several potential causes, including problems caused by a bug in one of the services that make up Cloudflare's software stack.
We know that our testing platform will inevitably miss some software bugs, so we built guardrails to gradually and safely release new code before a feature reaches all users. Health Mediated Deployments (HMD) is Cloudflare’s data-driven solution to automating software updates across our global network. HMD works by querying Thanos, a system for storing and scaling Prometheus metrics. Prometheus collects detailed data about the performance of our services, and Thanos makes that data accessible across our distributed network. HMD uses these metrics to determine whether new code should continue to roll out, pause for further evaluation, or be automatically reverted to prevent widespread issues.
Cloudflare engineers configure signals from their service, such as alerting rules or Service Level Objectives (SLOs). For example, the following Service Level Indicator (SLI) checks the rate of HTTP 500 errors over 10 minutes returned from a service in our software stack.
sum(rate(http_request_count{code="500"}[10m])) Continue reading