Ravie LakshmananJun 03, 2026Vulnerability / Server Security
Cybersecurity researchers have discovered a remote denial-of-service exploit that affects major web servers, including NGINX, Apache HTTPD, Microsoft IIS, Envoy, and Cloudflare Pingora.
The vulnerability has been codenamed HTTP/2 Bomb by Calif.
"The vulnerable behavior exists in each server's default HTTP/2 configuration," the company said, adding it was discovered by OpenAI Codex by chaining together two known techniques: a compression bomb and a Slowloris-style hold.
"The bomb targets HPACK, HTTP/2's header compression scheme: one byte on the wire becomes one full header allocation on the server, repeated thousands of times per request," Calif added. "The hold is a zero-byte flow-control window that keeps the server from ever freeing any of it."
