--- title: Cloudflare Zero-day: Accessing Any Host Globally | daily.dev description: A zero-day vulnerability in Cloudflare's WAF allowed attackers to bypass security rules and access origin servers globally through the... canonical: https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Cloudflare Zero-day: Accessing Any Host Globally | daily.dev og:description: A zero-day vulnerability in Cloudflare's WAF allowed attackers to bypass security rules and access origin servers globally through the... og:url: https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq og:image: https://api.daily.dev/og/posts/Sa1915UIq.png og:image:alt: Cloudflare Zero-day: Accessing Any Host Globally og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Cloudflare Zero-day: Accessing Any Host Globally **[Tech Lead Digest](https://daily.dev/sources/techleaddigest)** · 1 min read · 0 upvotes · 0 comments ## Summary A zero-day vulnerability in Cloudflare's WAF allowed attackers to bypass security rules and access origin servers globally through the /.well-known/acme-challenge/ path. The vulnerability exploited the ACME HTTP-01 certificate validation mechanism, exposing protected origins despite WAF protections. Cloudflare has since patched the issue, but the discovery highlights critical security considerations for certificate validation paths and WAF rule configurations. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [How we mitigated a vulnerability in Cloudflare’s ACME validation logic](https://daily.dev/posts/how-we-mitigated-a-vulnerability-in-cloudflare-s-acme-validation-logic-u8zxtoxa2) · Cloudflare · 0 upvotes · 0 comments - [The Cloudflare Outage May Be a Security Roadmap – Krebs on Security](https://daily.dev/posts/the-cloudflare-outage-may-be-a-security-roadmap-krebs-on-security-a9zczwqjp) · Krebs on Security · 0 upvotes · 0 comments - [You Don’t Need a 0-Day for RCE: A Real-World Kill Chain](https://daily.dev/posts/you-don-t-need-a-0-day-for-rce-a-real-world-kill-chain-dhogdo4ll) · InfoSec Write-ups · 0 upvotes · 0 comments --- Tags: [#security](https://daily.dev/tags/security), [#vulnerability](https://daily.dev/tags/vulnerability), [#cloudflare](https://daily.dev/tags/cloudflare), [#web-security](https://daily.dev/tags/web-security) [View this post on daily.dev](https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Cloudflare Zero-day: Accessing Any Host Globally","url":"https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq"},"datePublished":"2026-01-25T19:14:22.089Z","dateModified":"2026-02-28T04:40:21.095Z","description":"A zero-day vulnerability in Cloudflare's WAF allowed attackers to bypass security rules and access origin servers globally through the...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/bdc07c228bdae7a3656829abe48b96ea?_a=AQAEulh","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/bdc07c228bdae7a3656829abe48b96ea?_a=AQAEulh","isAccessibleForFree":true,"articleSection":"Tech Lead Digest","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Tech Lead Digest","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/6ed1ee1a2e5c49f698265a6b2912b80d","url":"https://daily.dev/sources/techleaddigest"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/cloudflare-zero-day-accessing-any-host-globally-sa1915uiq","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"security,vulnerability,cloudflare,web-security","timeRequired":"PT1M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Tech Lead Digest","item":"https://daily.dev/sources/techleaddigest"},{"@type":"ListItem","position":3,"name":"Cloudflare Zero-day: Accessing Any Host Globally"}]} ```