The Cloudflare Global Outage of November 18, 2025: An In-Depth Analysis of Impact, Causes, and Future Implications for Internet Resilience

Accident Overview: The Cloudflare Global Outage of November 18, 2025

On November 18, 2025, Cloudflare experienced a significant global outage that severely impacted its network and the numerous internet services relying on its infrastructure. This incident was characterized by widespread 500 errors and affected millions of users and thousands of websites worldwide .

Timeline of the Outage

The disruption commenced at approximately 11:20 UTC on November 18, 2025, with Cloudflare's network beginning to experience significant failures in delivering core network traffic 1. Cloudflare officially acknowledged internal service degradation and initiated an investigation around 11:40-11:48 UTC 2. The timeline of key events is detailed below:

The period of significant impact lasted approximately 3 hours and 10 minutes, from 11:20 UTC to 14:30 UTC, while full restoration of all systems took about 5 hours and 46 minutes, concluding at 17:06 UTC 1.

Specific Cloudflare Services Impacted

The outage led to significant failures across Cloudflare's global network, affecting both its internal services and a vast array of customer-facing platforms. Cloudflare's own services experienced degraded performance, including Cloudflare Sites and Services, Bot Management, CDN/Cache, Dashboard, Firewall, Network, and Workers 2. Additionally, Cloudflare Access and WARP were affected, with WARP access being temporarily disabled in London during the incident 2.

Customers encountered prevalent errors such as "Internal server error Error code 500" 4 and a high volume of 5xx HTTP status codes 1. Numerous external platforms and applications that rely on Cloudflare's infrastructure became inaccessible, including major services like X (formerly Twitter), ChatGPT, Canva, Grindr 4, Discord , and Shopify . Even outage tracking sites such as Downdetector.com and Pingdom.com appeared to experience issues themselves 3. Cloudflare's own status page also went down temporarily, which initially complicated their response and led them to suspect a broader attack 1.

Geographical Scope of the Disruption

The disruption was global, affecting websites and users across the entire world 3. Cloudflare's status page reported a "Partial Outage" in numerous cities spanning Africa, Asia, Europe, Latin America & the Caribbean, the Middle East, North America, and Oceania 2. London was specifically noted as WARP access was temporarily disabled there 2.

Initial Technical Trigger and Underlying Cause

Cloudflare confirmed that the outage was not the result of a cyberattack or malicious activity 1. The technical trigger was identified as an inadvertent change to permissions within one of Cloudflare's database systems 1. This permission modification caused the ClickHouse database to output multiple, duplicate entries into a "feature file" utilized by the Bot Management system 1.

The underlying cause lay within a specific Rust code component in the Bot Management system, specifically within the fl2_worker_thread 1. This component had a hard limit on the size of the feature file it processed 1. When the influx of duplicate entries caused the file to exceed this size limit, the Rust code, instead of handling the error gracefully, invoked Result::unwrap on an Err value, leading the thread to panic and crash the core proxy modules 1. The duplication of entries in the feature file was traced back to a database migration involving ClickHouse, where a query against system.columns returned duplicate rows because users had been granted access to an additional backing database 1.

Public Reactions and Media Coverage

The global outage immediately triggered widespread public reaction and extensive media coverage. Users across the internet reported "widespread 500 errors" and often initially suspected issues with their own internet connections before realizing the scale of the Cloudflare problem . Social media platforms, particularly X (formerly Twitter), saw over 11,500 problem reports 7, with major media outlets quickly highlighting disruptions to prominent services like ChatGPT and X . The inaccessibility of Cloudflare's own status page for parts of the incident compounded user frustration and prevented timely updates . Within online technical communities, such as r/sysadmin and Hacker News, administrators engaged in discussions that blended "hugops" (sympathetic support) with "gallows humor" regarding the initial panic before the cause was known 7.

Media commentary frequently underscored the "fragility" and "interconnectedness" of the modern digital ecosystem, drawing parallels to recent outages at Amazon Web Services and Microsoft Azure in October 2025 . While Cloudflare's team initially suspected a hyper-scale DDoS attack due to the fluctuating nature of the errors and the coincident unavailability of its status page 6, external commentary largely confirmed the reported impact and Cloudflare's rapid efforts toward resolution . There were no external critiques contradicting Cloudflare's eventual detailed technical explanation of the root cause 8. Instead, expert and media commentary broadened the discussion to emphasize the critical need for "cyber resilience," highlighting how "one small mistake gets amplified everywhere at once" in highly automated, globally distributed systems 8.

Impact Assessment: Economic and Operational Consequences of the Cloudflare Outage

The Cloudflare outage on November 18, 2025, caused widespread disruption across the internet, highlighting the critical dependency of numerous online services on its infrastructure and underscoring the potential for cascading failures within the internet ecosystem 9. Lasting approximately four hours and ten minutes for significant impact, with full restoration taking about 5 hours and 46 minutes, the incident broadly affected thousands of websites and applications globally .

Operational Disruptions and End-User Impact

The outage led to extensive operational disruptions and negative impacts on end-users and internet traffic flow worldwide .

• Service Unavailability: End-users encountered "widespread 500 errors" and were unable to access numerous websites and applications, often being met with error pages . Many initially suspected their own internet connections before realizing it was a broader Cloudflare issue 7.
• Increased Latency: Cloudflare's network experienced significant failures to deliver core network traffic and observed substantial increases in latency of responses from its Content Delivery Network (CDN) during the incident .
• Productivity Losses: Businesses heavily reliant on affected platforms, such as ChatGPT for content creation or Canva for design, experienced work stoppages as employees could not perform core job functions 9.
• Authentication Failures: Cloudflare Access users faced widespread authentication failures, which prevented logins to target applications 6.
• Reduced Spam Detection: The Email Security service temporarily lost access to an IP reputation source, leading to reduced spam-detection accuracy, though no critical customer impact was reported 6.
• Dashboard Issues: Cloudflare's own dashboard was affected, making it impossible for users to log in due to Turnstile being unavailable. It later experienced elevated latency from a backlog of login attempts 6.

Major Websites and Services Affected

The outage broadly impacted thousands of websites and applications that rely on Cloudflare's CDN and other services . Services exhibiting degraded performance included Cloudflare Sites and Services, Bot Management, CDN/Cache, Dashboard, Firewall, Network, and Workers 2. External platforms relying on Cloudflare became inaccessible, leading to a significant list of disrupted services:

Estimated Financial Losses and Quantifiable Metrics

The financial impact of the Cloudflare outage was substantial for businesses globally, underscoring the high cost of downtime in the digital economy 9:

• Downtime Costs:
  • Large enterprises reportedly lose an average of $5,600 to $9,000 per minute of downtime 9.
  • A significant 93% of enterprises report downtime costs exceeding $300,000 per hour 9.
  • Nearly half (48%) of enterprises experience hourly costs surpassing $1 million 9.
  • For Fortune 500 companies, average costs range from $500,000 to $1 million per hour 9.
• Aggregate Impact: Given the approximately 4-hour duration of significant impact and the thousands of websites affected, the total aggregate global economic impact likely exceeded hundreds of millions of dollars 9.
• Cloudflare's Market Share: Cloudflare's substantial market presence, powering over 20% of all websites globally and processing an estimated 20% of all internet traffic, means its failures have widespread and severe implications .

Broader Economic and Operational Consequences

Beyond direct revenue loss and service unavailability, the outage incurred several hidden costs and broader consequences:

• Customer Trust Erosion: Studies indicate that 88% of users are less likely to return to a website after a poor experience, directly impacting customer loyalty and future business 9.
• SEO Penalties: Extended downtime can negatively affect search engine rankings, as site availability is a crucial ranking factor, potentially leading to long-term visibility issues 9.
• Support Costs: Customer service teams across various affected organizations were overwhelmed with inquiries, leading to increased labor costs and strain on resources 9.
• Reputation Damage: In an "always-on" digital economy, widespread outages generate negative social media coverage and can significantly harm brand perception for both Cloudflare and its customers 9.
• Single Point of Failure Vulnerability: The incident starkly underscored the internet's vulnerability to single points of failure in critical infrastructure 9. Media commentary frequently emphasized the "fragility" and "interconnectedness" of the modern digital ecosystem, drawing parallels to previous significant outages involving Amazon Web Services (October 20, 2025), Fastly (June 2021), and Dyn (October 2016) . Experts highlighted the "paradox of centralization," where a handful of companies control infrastructure for millions of websites, leading to cascading failures when one experiences an issue 9. This serves as a potent reminder for businesses about the critical importance of infrastructure resilience, redundancy planning, and understanding the hidden risks of centralized internet services 9.

Root Cause Analysis and Resolution Process

The global outage experienced by Cloudflare on November 18, 2025, was not the result of a cyberattack or malicious activity, but rather a complex chain of technical failures originating from an inadvertent configuration change 1. This section details the immediate trigger, underlying vulnerabilities, specific technical failures, and the subsequent diagnostic and resolution processes employed by Cloudflare.

Technical Root Cause

The immediate trigger for the outage was an "inadvertent change to permissions within one of Cloudflare's database systems" 6, which affected a ClickHouse database cluster 1. This permission change, made around 11:05 UTC, allowed ClickHouse queries to run under initial user accounts and explicitly access metadata for tables in the r0 database 6.

This seemingly minor modification exposed a pre-existing vulnerability in a query used to construct a "feature file" for Cloudflare's Bot Management system 1. The query, SELECT name, type FROM system.columns WHERE table = 'http_requests_features' order by name;, lacked a filter for database name 6. Consequently, with the new r0 access, the query began returning duplicate entries from the r0 schema, effectively doubling the number of rows (features) in the final output file 6. This oversized feature file was then propagated to all network machines running traffic routing software 6.

A critical underlying vulnerability was a hardcoded size limit within a specific Rust code component of the Bot Management system, residing in the fl2_worker_thread 1. This limit, set to 200 machine learning features, was intended for memory preallocation to optimize performance 6. When the expanded feature file, containing more than 200 entries, exceeded this preallocated memory limit, the Rust code failed to handle the error gracefully 6. Instead, it called Result::unwrap on an Err value, causing the fl2_worker_thread to panic and crash core proxy modules across Cloudflare's network 1. This cascading failure led to widespread service degradation and HTTP 5xx errors 1.

The bug was classified as a "latent bug"—an error hidden within the system that only manifested under a specific and unusual combination of conditions, in this case, a routine configuration change interacting with an underlying query flaw 11.

Diagnosis and Resolution Process

Cloudflare's engineering teams initiated an immediate investigation upon detecting internal service degradation and unusual traffic spikes around 11:40-11:48 UTC 2. The intermittent nature of the initial outage, with systems recovering and then failing again every five minutes due to the periodic regeneration of the faulty feature file, initially led Cloudflare to suspect a hyper-scale Distributed Denial of Service (DDoS) attack 6. Further complicating diagnostics was the concurrent, unrelated outage of Cloudflare's independently hosted status page, which initially suggested a broader attack 1.

The core issue was identified as a faulty configuration file 2, specifically the oversized bot management feature file 1. Resolution efforts faced challenges as there was no immediate mechanism to "insert a good file into the queue" 1. To rectify the situation, Cloudflare's team resorted to rebooting processes across a multitude of machines globally to force them to flush the corrupted configuration files 1. This process also involved isolating the malfunctioning component and temporarily disabling WARP services in London as a remediation step 2. By stopping the propagation of the faulty feature file and manually inserting a known good version, the core issue was effectively addressed 6.

Restoration Timeline

The restoration process unfolded over several hours:

The period of significant impact lasted approximately 3 hours and 10 minutes (from 11:20 UTC to 14:30 UTC), while full restoration of all systems took about 5 hours and 46 minutes (from 11:20 UTC to 17:06 UTC) 1. After the fix, teams continuously monitored the system for errors and latency, confirming a return to normal service levels 2.

Communication Strategies

Throughout the incident, Cloudflare maintained a transparent communication strategy:

• Status Page Updates: Regular updates were posted on the Cloudflare System Status page, progressing from "Investigating" to "Identified," "Update," "Monitoring," and "Operational" 2.
• Emailed Statements: Emailed statements were issued, confirming internal service degradation and initial observations of unusual traffic spikes 5.
• Rapid Post-Mortem Release: A detailed post-mortem report was published within 24 hours of the outage, providing significant technical detail on the cause, impact, and remediation efforts 1.
• Leadership Involvement and Transparency: Cloudflare's CEO, Matthew Prince, was directly involved in authoring the post-mortem, collaborating with the former CTO and Chief Legal Officer to ensure accuracy. He emphasized the company's commitment to transparency 1. The company's CTO also issued a public apology and committed to transparent communication 11.

Preventative Measures and Lessons Learned

To prevent similar incidents, Cloudflare outlined several hardening measures and lessons learned:

• Configuration File Ingestion: Hardening the ingestion process for Cloudflare-generated configuration files 1.
• Global Kill Switches: Enabling more global kill switches for features to allow for faster mitigation of problematic deployments 1.
• Error Report Management: Eliminating the ability for error reports to overwhelm system resources 1.
• Failure Mode Review: Thoroughly reviewing failure modes for error conditions across all core proxy modules 1.
• Robust Error Handling: Implementing more robust error handling and boundary checks in critical software components to prevent unhandled panics 6.

The incident also served as a broader reminder of the internet's dependence on central providers like Cloudflare and underscored the importance of cyber resilience, advocating for diversification, redundant DNS providers, multi-CDN strategies, and robust incident response plans 8.

Preventative Measures and Future Implications

The Cloudflare outage of November 18, 2025, served as a stark reminder of the internet's inherent vulnerabilities, prompting significant introspection within Cloudflare and across the broader industry. This section details the corrective actions and new protocols initiated by Cloudflare, examines the industry-wide dialogue on internet resilience, draws comparisons to previous outages to distill critical lessons, and outlines recommendations for building a more robust and fault-tolerant internet infrastructure.

Cloudflare's Post-Incident Remediation and Proactive Measures

Following the November 2025 incident, Cloudflare immediately outlined several key remediation and follow-up steps to address the root causes and enhance system stability. These measures, alongside prior initiatives, aim to fortify their infrastructure against future disruptions.

Key Remediation Efforts Post-November 2025 Outage

The primary cause of the outage was a permissions change in a database system, leading to an oversized "feature file" that caused the software (FL2 Rust code) to panic and generate HTTP 5xx errors across the network 6. In response, Cloudflare has committed to:

• Configuration File Hardening: Treating Cloudflare-generated configuration files with the same rigor as user-generated input 6.
• Global Kill Switches: Implementing more global kill switches for features, allowing for rapid disabling of problematic components 6.
• Resource Protection: Eliminating the potential for core dumps or other error reports to overwhelm system resources 6.
• Error Condition Review: A thorough review of failure modes for error conditions across all core proxy modules 6.
• Panic Handling: Discussions on platforms like Hacker News highlighted the use of .unwrap in the Rust code as a panic trigger, rather than a mechanism for graceful error handling. This spurred suggestions for improved error handling and panic isolation, potentially by implementing clippy::unwrap_used or utilizing expect with descriptive messages 1.
• Deployment Methodology: Critics also pointed out the absence of explicit mentions for canary deployments, incremental or wave-based configuration rollouts, and rapid rollback methodologies in Cloudflare's initial remediation plan, questioning how the blast radius would be contained 1.

Prior Initiatives for Enhanced Resilience

Prior to the November 2025 event, Cloudflare had already embarked on several significant initiatives following earlier incidents to improve its resilience:

• "Code Orange" Process: A plan to implement a crisis response process akin to Google's, enabling the shift of engineering resources to address significant events 15.
• Distributed Control Plane: Efforts to decouple the control plane configuration from core data centers, ensuring its functionality even if central facilities are offline 15.
• High Availability Enforcement: Mandating that all Generally Available (GA) products and features rely on a high availability cluster, minimizing dependencies on specific facilities 15.
• Disaster Recovery Planning: Requiring all GA products to possess a reliable and tested disaster recovery plan 15.
• Chaos Testing: Implementing more rigorous chaos testing across all data center functions, including the simulated complete removal of core data center facilities 15.
• Auditing and Logging: Conducting thorough audits of core data centers and establishing a disaster recovery plan for logging and analytics to prevent data loss 15.
• Workers KV Redesign: Following a June 2025 outage, Cloudflare redesigned Workers KV to store all data on its own infrastructure, eliminating reliance on a single third-party cloud provider and serving all requests from its own infrastructure for enhanced redundancy and high availability. This involved a distributed database sharded across multiple clusters and a hybrid storage architecture leveraging R2 for larger objects, alongside dual-provider capabilities for writes and raced reads to maintain consistency 16.

Broader Industry Dialogue on Internet Resilience

The November 2025 outage reignited critical industry discussions regarding internet resilience, emphasizing distributed architectures and the mitigation of single points of failure.

The Centralization Paradox and Distributed Models

The incident underscored the "centralization paradox," where the efficiency and performance benefits offered by major providers like Cloudflare and AWS inadvertently create systemic vulnerabilities that can cascade across the internet during failures 9. This has highlighted the benefits of truly distributed or decentralized systems, with observations that "legacy setups" or systems running on bare metal without reliance on such centralized services often survived outages, suggesting a move towards more distributed models 17.

Automation Risks and Dependency Management

The root cause, an automatically generated configuration file, emphasized that while automation boosts efficiency, it can amplify errors without robust safeguards like oversight, size limits, and validation checks 9. The discussion extended to concerns about "Vibe Coding" or AI-generated code potentially leading to hard-to-debug infrastructure issues 17. Furthermore, the outage demonstrated how many services not directly using Cloudflare were still affected due to indirect dependencies, underscoring the necessity of understanding the complete dependency chain 9. There is also an ongoing debate regarding balancing the need for rapid configuration updates to combat evolving threats against the safety concerns of pushing potentially flawed updates quickly to a global network 1.

Lessons from Major Infrastructure Outages: A Comparative Analysis

The November 18, 2025, Cloudflare outage shares commonalities with, and offers distinct lessons from, previous major internet infrastructure failures.

Recurring Themes: Configuration Errors and Centralized Failures

Several recurring themes emerge when comparing this incident to past outages:

• Configuration Errors as Root Causes: Similar to the June 2021 Fastly outage 9 and a July 2019 Cloudflare outage 9, the November 2025 event was traced to a configuration file error. This highlights the vulnerability of even sophisticated systems to human or automated configuration mistakes.
• Centralized Dependencies: Like the AWS outage in October 2025 (DNS and DynamoDB API failures) 9 and the Dyn DDoS attack in October 2016 9, the Cloudflare outage showcased how failures in a central infrastructure provider can have a massive, cascading impact across numerous internet services.
• Cascading Failures: The oversized configuration file didn't solely impact one service but triggered crashes across multiple interconnected systems, illustrating how single points of failure can amplify problems in complex architectures 9.
• No Provider is Immune: The incident reaffirms that even large, well-resourced providers like Cloudflare and AWS are susceptible to failures 9.

Unique Insights from the November 2025 Incident

The November 2025 outage also provided unique lessons:

• Rust .unwrap and Panic: The technical details, specifically the .unwrap call in Rust code leading to a system panic when a size limit was exceeded, spurred extensive discussions among developers about best practices for error handling in Rust in production environments 6.
• Bot Management System Context: The failure originated in the bot management system, which relies on rapidly updated feature files to counter evolving threats 6. This introduces a unique challenge in balancing the need for quick updates against the risk of rapid propagation of flawed configurations.
• Severity: Cloudflare's CEO described it as their "worst outage since 2019," noting that previous outages had primarily impacted dashboards or newer features, rather than the core traffic flow to this extent 6.

Strategies for Building Resilient Internet Infrastructure

Experts and industry bodies emphasize several best practices to enhance internet infrastructure resilience and incident preparedness.

Redundancy and Multi-CDN Approaches

To mitigate the risks associated with centralized dependencies, organizations should consider:

• Multi-CDN Architecture: Distributing traffic across multiple Content Delivery Network (CDN) providers using primary/backup configurations with DNS failover, active/active setups based on real-time performance, or geographic distribution to minimize localized outage impact 9.
• DNS-Based Failover: Implementing automated DNS failover with continuous health checks for HTTP/HTTPS availability, response times, and content validation. Utilizing low Time-To-Live (TTL) values (60-300 seconds) for critical services ensures faster failover propagation, with services like AWS Route 53, NS1, and Cloudflare offering these capabilities 9.
• Origin Shield Implementation: Employing an intermediate caching layer between CDN edge servers and the origin infrastructure to reduce origin load and maintain caching even if the primary CDN fails 9.
• Edge Computing and Distributed Architecture: Processing data and application logic closer to users to reduce latency and improve resilience, enabling applications to function even if central locations are affected. Examples include Cloudflare Workers, AWS Lambda@Edge, and Fastly Compute@Edge 9.
• Decentralized CDN Architecture: Exploring emerging technologies like peer-to-peer (e.g., IPFS) and blockchain-based CDNs (e.g., Theta Network) to eliminate central points of failure and enhance decentralization 9.

Robust Incident Response and Operational Best Practices

Beyond architectural redundancy, operational excellence and preparedness are crucial:

• Comprehensive Monitoring and Alerting: Implementing multi-layer monitoring, including synthetic monitoring, Real User Monitoring (RUM), infrastructure monitoring, and CDN-specific monitoring. Alert configurations should include escalation chains, threshold-based alerts, alert grouping, and runbooks for incident response 9.
• Disaster Recovery and Business Continuity Planning: Documenting clear procedures for infrastructure failures, including risk assessment, defining Recovery Time Objectives (RTO) and Recovery Point Objectives (RPO), establishing incident response procedures, regular testing (quarterly drills, tabletop exercises, full-scale failover tests), and preparing communication plans for status page updates, internal notifications, and external communications 9.
• Automation with Safeguards: Ensuring automated systems have robust oversight, size limits, validation checks, canary deployments, and circuit breakers to prevent cascading failures 9.
• Understand Service Level Agreements (SLAs): Organizations must be aware of CDN provider SLAs, their limitations (e.g., credits often limited to service fees, not business losses), and the process for claiming credits 9.
• Dependency Mapping: Understanding the complete chain of dependencies for all services is essential to identify and mitigate hidden risks 9.

The table below summarizes key recommendations for resilient infrastructure:

Conclusion

The November 2025 Cloudflare outage underscores the persistent challenges in maintaining robust internet infrastructure. Cloudflare's detailed remediation efforts, focusing on configuration hardening, enhanced error handling, and robust deployment practices, alongside its ongoing commitment to distributed architectures and chaos testing, are crucial steps towards mitigating future incidents. The broader industry conversation highlights the critical need to address the "centralization paradox" and actively pursue truly distributed models, recognizing the inherent risks of automation without sufficient safeguards. By learning from past mistakes, both common (configuration errors, centralized dependencies) and unique (Rust .unwrap impact), the industry can advance towards more resilient systems. Implementing comprehensive strategies for redundant infrastructure, multi-CDN approaches, rigorous monitoring, and meticulous disaster recovery planning, coupled with an understanding of evolving regulatory landscapes and future technologies like AI-powered traffic management, will be paramount in safeguarding the future of the interconnected internet. The takeaway is clear: continuous vigilance, architectural foresight, and operational discipline are non-negotiable for internet infrastructure providers and consumers alike.