Cloudflare Says It Mitigated Record 11.5 Tbps Volumetric DDoS Attack

What Cloudflare reported

Internet infrastructure company Cloudflare said it recently blocked the largest recorded volumetric distributed denial-of-service (DDoS) attack, which peaked at 11.5 terabits per second (Tbps).

Cloudflare said it recently blocked the largest recorded volumetric distributed denial-of-service (DDoS) attack, which peaked at 11.5 terabits per second (Tbps).

The company did not disclose detailed attribution in the public summary, but the announcement underscores continued escalation in raw attack bandwidth confronting internet-facing services and edge providers.

Background and context: why this matters

DDoS attacks flood a target with traffic or requests to exhaust its network, compute, or application capacity and render services unavailable. Over the last decade the metric for “largest” attacks has shifted from gigabits per second (Gbps) to terabits per second (Tbps) as attackers and botnets have leveraged more powerful amplification vectors and larger compromised infrastructure.

• Scale matters because volumetric attacks at Tbps size can saturate transit links, overwhelm peering and scraping protections, and create collateral damage for networks and third parties.
• Even when a protected service is insulated by a mitigation provider, upstream congestion and cross‑traffic effects can interrupt unrelated customers and degrade internet performance regionally.
• The growing scale reflects both the availability of amplification techniques and the proliferation of misconfigured or compromised internet‑facing devices that can be leveraged as reflectors or botnet endpoints.

Technical analysis and expert commentary for practitioners

For network operators, CDN engineers, and security teams, the headline number (11.5 Tbps) is a prompt to reassess capacity planning, mitigation playbooks and telemetry. Key considerations:

• Edge and backbone capacity: Any mitigation strategy depends on headroom—either within an edge network or by steering traffic to resilient scrubbing centers. Providers that operate large anycast networks and have extensive peering relationships are better positioned to absorb and disperse very large volumetric attacks.

• Detection and telemetry: Early, high-fidelity telemetry is essential. Teams should instrument both flow-level (NetFlow/IPFIX) and application-level metrics to detect sudden shifts in traffic composition and to distinguish legitimate spikes (e.g., flash crowds) from malicious floods.

• Automated mitigation orchestration: Manual responses are too slow at Tbps events. Automated playbooks that can trigger routing changes, apply scrubbing rules, or scale scrubbing capacity reduce time-to-mitigation and collateral impact.

• Rate limiting vs scrubbing: Simple rate limiting at origin can be counterproductive for large attacks because it can fragment legitimate traffic. Dedicated scrubbing—identifying malicious flows and separating them from legitimate traffic—is the more robust approach.

• Upstream coordination: When attacks approach backbone capacity, coordination with transit providers, IXPs and peers is necessary. Techniques such as BGP announcements to steer traffic to mitigation clouds, Flowspec rules, and temporary blackholing of specific prefixes can be part of a layered response.

Comparable cases and observed trends

Public DDoS records over the last decade show a steady increase in peak attack volumes. A widely reported example from 2018 targeted GitHub via memcached amplification and reached more than 1 Tbps, a level that at the time shattered previous records. The 11.5 Tbps event Cloudflare describes is several times larger, illustrating how the upper bounds of volumetric attacks have expanded.

Trends practitioners should note:

• Amplification vectors remain a key driver of volumetric scale. Misconfigured UDP-based services and reflective protocols can multiply attacker bandwidth many times over.
• Botnets of compromised hosts (IoT devices, poorly secured servers) continue to provide attacker foot soldiers, and their size and distribution enable multi-vector, multi-protocol campaigns.
• Attackers increasingly combine high-volume flooding with application-layer probing to force defenders to choose between blocking aggressive layers and risking collateral damage to legitimate users.

Potential risks, implications and actionable recommendations

Risks from large volumetric DDoS attacks extend beyond immediate service outages:

• Collateral disruption to ISPs and shared infrastructure when transit and peering links are saturated.
• Operational strain and human error during high-pressure mitigation events, which may lead to misconfigurations or prolonged outages.
• Ransom and extortion dynamics where attackers threaten sustained or repeated high‑capacity attacks.

Actionable recommendations for organizations and network teams:

• Engage a proven DDoS mitigation partner and conduct regular tabletop exercises. Test escalation paths, automated rule sets, and the operational handoffs between on‑call engineers and mitigation services.

• Audit and harden exposure to amplification vectors. Close or properly configure UDP services that can be used for reflection/amplification (e.g., memcached, CLDAP, NTP). Where services must remain open, apply access controls and monitoring.

• Design networks for diversity and absorbency: multiple transit providers, strong peering relationships, and capacity planning that accounts for regional surges and the possibility of Tbps-class events.

• Implement granular, telemetry-driven scrubbing rather than blunt blackholing. Preserve legitimate traffic where possible and document fallback procedures for when full scrubbing is not feasible.

• Share intelligence with industry partners, ISPs and national CERTs. Large volumetric attacks often leverage common infrastructure; collective action can reduce reuse of reflectors and slow attackers’ ability to scale.

• Prepare communications templates for customers and stakeholders so that during an event accurate status updates and guidance can be issued without delaying technical responses.

Conclusion

Cloudflare’s report that it blocked an 11.5 Tbps volumetric DDoS attack highlights how attack capacity has grown into the multiple‑terabit range. For defenders this escalation is a reminder to invest in layered mitigation—capacity, telemetry, automation, and upstream coordination—rather than relying on ad hoc responses. Regular testing, hardening of amplification vectors, and partnerships with experienced scrubbing providers remain the most effective ways to maintain availability and limit collateral damage when attacks scale to these unprecedented sizes.

Source: www.bleepingcomputer.com