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Cloudflare traced its November 18, 2025 outage to an internal permissions change that caused a Bot Management configuration file to grow beyond a software limit and trigger failures in its core proxy. The company said the incident was not caused by a cyberattack. The disruption affected Cloudflare services and customers that relied on them, with core traffic largely recovered before all systems were fully restored.
What caused the Cloudflare outage?
A gradual change to permissions in Cloudflare’s ClickHouse database system altered the output of a query that generated a feature file used by its Bot Management software. The query began producing duplicate entries, making the file too large for the software to load. Cloudflare’s postmortem describes the sequence in detail: Cloudflare’s November 18 outage report.
How a routine change led to proxy failures
The query ran every five minutes. As the permissions update spread across database nodes, some initially produced the faulty output while others continued producing the correct file. Cloudflare’s network therefore alternated between good and bad files, contributing to fluctuating failures and spikes in HTTP 5xx errors. Once all ClickHouse nodes were producing the faulty configuration, the failures stopped fluctuating and became easier to diagnose.
The oversized file crossed a software limit when loaded, causing failures in Cloudflare’s core proxy. The failure was therefore a chain of internal software and configuration effects, rather than an attack on the network.
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Was the Cloudflare outage a cyberattack?
No. Cloudflare said the problem was not caused, directly or indirectly, by a cyberattack or malicious activity. SANS NewsBites reproduced the company’s statement: “the issue was not caused, directly or indirectly, by a cyber attack or malicious activity of any kind.” SANS NewsBites’ November 21 account also summarized the incident and its operational implications.
When did the outage happen, and when was service restored?
The incident occurred on November 18, 2025. The sources give slightly different start times, so the most accurate summary is that it began between 11:20 and 11:28 UTC. Cloudflare’s postmortem, as recounted by Dark Reading, gives 11:20 UTC; SANS NewsBites gives 11:28 UTC. Dark Reading’s November 19 report covers the postmortem and the discrepancy.
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| Time (UTC) | What happened |
|---|---|
| 11:20–11:28 | Reported start of the incident: 11:20 in Cloudflare’s account as reported by Dark Reading, and 11:28 in SANS NewsBites. |
| 14:30 | Cloudflare said core traffic was largely flowing as normal. |
| 17:06 | Cloudflare said all systems were functioning normally; SANS described downstream services as restarted and operations fully restored. |
The distinction matters: core traffic was largely back to normal at 14:30 UTC, but full restoration was not reported until 17:06 UTC.
Who and what did the outage affect?
The failures affected Cloudflare network services and organizations and users relying on them. Contemporary reporting named X, Uber, Canva, and ChatGPT among services affected. These are examples, not a complete list. The sources cited here do not establish an outage-specific percentage of customers, websites, or Internet traffic affected, so a precise overall share cannot be stated from them.
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How did Cloudflare recover?
Cloudflare stopped generating and distributing the faulty file, put a known-good file back in place, and restarted its core proxy. That sequence addressed both the bad configuration and the software process that had loaded it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What can organizations learn from the outage?
For organizations that depend on cloud, security, or proxy providers, the practical response is to prepare for a provider failure before one occurs. SANS NewsBites editor John Pescatore recommended keeping an accurate, current inventory of security-as-a-service and proxy-based services, understanding common dependencies across suppliers, and maintaining outage workaround plans.
Rank #4
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Map critical dependencies
- Record which business services depend on each provider, including indirect dependencies such as shared infrastructure or security services.
- Identify whether apparently separate providers rely on the same underlying supplier or network, since that can limit the value of a backup.
Define and exercise workarounds
- Specify who can authorize a workaround, how it will be activated, and which functions may be degraded or unavailable during recovery.
- Exercise continuity and disaster-recovery procedures so teams can test decision-making and communications under realistic failure conditions.
- Assess security and performance trade-offs before rerouting traffic. Sending a site directly to its origin, for example, may remove protections and caching that a proxy provider supplies.
These measures reduce uncertainty and can improve recovery readiness; they cannot guarantee uninterrupted service. Cloudflare CEO Matthew Prince wrote in the postmortem, “Any outage of any of our systems is unacceptable.” The incident shows why operational resilience must account for the possibility that even a routine internal change can disrupt a widely used service.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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