Cloudflare blocks largest recorded DDoS attack peaking at 11.5 Tbps

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).

In volumetric DDoS attacks, attackers overwhelm the target with massive amounts of data, consuming the bandwidth or exhausting system resources, leaving legitimate users with no access to the targeted servers and services.

"Cloudflare's defenses have been working overtime. Over the past few weeks, we've autonomously blocked hundreds of hyper-volumetric DDoS attacks, with the largest reaching peaks of 5.1 Bpps and 11.5 Tbps," the company said in a Tuesday tweet.

While Cloudflare initially stated that the 11.5 Tbps UDP flood attack lasted approximately 35 seconds and primarily originated from Google Cloud, the company later issued a correction, saying that the "attack in fact came from a combination of several IoT and cloud providers."

"Our abuse defenses detected the attack, and we followed proper protocol in customer notification and response. Initial reports suggesting that the majority of traffic came from Google Cloud are not accurate," a Google Cloud spokesperson also told BleepingComputer.

This comes two months after Cloudflare announced another record-breaking 7.3 Tbps DDoS attack targeting an unnamed hosting provider in June. The previous record was of 3.8 Tbps and two billion packets per second (pps) in an attack that Cloudflare also blocked in October 2024.

Microsoft also mitigated a 3.47 Tbps volumetric DDoS attack in January 2022, when the attackers targeted an Azure customer from Asia. Another massive DDoS attack took down and disrupted multiple Microsoft 365 and Azure services worldwide in July 2024.

​In April, Cloudflare also revealed in its 2025 Q1 DDoS Report that it mitigated a record number of DDoS attacks in 2024, with a 198% quarter-over-quarter increase and a massive 358% year-over-year jump.

As the company stated, it mitigated a total of 21.3 million DDoS attacks that targeted Cloudflare's customers last year, as well as its own infrastructure in 6.6 million attacks over an 18-day multi-vector campaign.

"Of the 20.5 million DDoS attacks, 16.8M were network-layer DDoS attacks, and of those 6.6M targeted Cloudflare's network infrastructure directly," Cloudflare said at the time.

"These attacks were part of an 18 day multi-vector DDoS campaign comprising SYN flood attacks, Mirai-generated DDoS attacks, SSDP amplification attacks to name a few."

The most significant spike was seen by network-layer attacks, which also saw the sharpest growth since the start of 2025, reaching a 509% YoY increase.

Update September 03, 01:35 EDT: Added Google statement.