New ‘HTTP/2 Rapid Reset’ zero-day attack breaks DDoS records

A new DDoS technique named ‘HTTP/2 Rapid Reset’ has been actively exploited as a zero-day since August, breaking all previous records in magnitude.

Since late August, Cloudflare has detected and mitigated over a thousand ‘HTTP/2 Rapid Reset’ DDoS attacks that surpassed 10 million rps, with 184 breaking the previous 71 million rps record.

Cloudflare is confident that as further threat actors employ more expansive botnets along with this new attack method, HTTP/2 Rapid Reset attacks will continue to break even greater records.

The novel attack exploits a zero-day vulnerability tracked as CVE-2023-44487, which abuses a weakness in the HTTP/2 protocol.

Simply put, the attack method abuses HTTP/2’s stream cancellation feature to continuously send and cancel requests, overwhelming the target server/application and imposing a DoS state.

All three firms conclude that the best approach for clients to counter HTTP/2 Rapid Reset attacks is to use all available HTTP-flood protection tools and bolster their DDoS resilience with multifaceted mitigations.

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