Bug 2485556

Summary: nginx: HTTP/2: Remote Denial of Service via compression bomb and Slowloris-style attack
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: kaycoth, rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in HTTP/2, affecting various web servers including NGINX. A remote attacker can exploit this vulnerability by combining an HPACK compression bomb with a zero-byte flow-control window. This technique allows a small amount of data to expand into large memory allocations on the server, which are then held, leading to a denial of service (DoS) by rendering the server inaccessible.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2485558    
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Description OSIDB Bzimport 2026-06-05 19:37:35 UTC 
We’re publishing HTTP/2 Bomb, a remote denial-of-service exploit against most major web servers, including:

nginx

Apache httpd

Microsoft IIS

Envoy

Cloudflare Pingora

The vulnerable behavior exists in each server's default HTTP/2 configuration.

The attack was discovered by Codex, which chained two techniques known to humans for a decade: 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. The hold is a zero-byte flow-control window that keeps the server from ever freeing any of it.

A curious search on Shodan revealed 880,000+ websites supporting HTTP/2 and running one of these servers, though many sit behind a CDN, which is much harder to bring down.

A home computer on a 100Mbps connection can render a vulnerable server inaccessible within seconds. Against Apache httpd and Envoy, a single client can consume and hold 32GB of server memory in roughly 20 seconds.
Comment 2 Marco Benatto 2026-06-05 20:20:55 UTC 
Upstream commit for this fix:
https://github.com/nginx/nginx/commit/365694160a85229a7cb006738de9260d49ff5fa2