Bug 2487465 (CVE-2026-47774)

Summary: CVE-2026-47774 envoy: envoy: HTTP/2 Remote Denial of Service via HPACK compression bomb and Slowloris-style attack
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: kaycoth
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A denial-of-service vulnerability was found in Envoy's HTTP/2 HPACK header compression implementation. A remote attacker could send a specially crafted HTTP/2 request that triggers disproportionately large memory allocations on the server, leading to resource exhaustion and denial of service.
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Description OSIDB Bzimport 2026-06-10 11:18:33 UTC 
A denial-of-service vulnerability was found in Envoy's HTTP/2 implementation. The attack chains two techniques: an HPACK compression bomb that exploits header compression to amplify a single byte on the wire into a full header allocation on the server (repeated thousands of times per request), and a Slowloris-style hold using a zero-byte HTTP/2 flow-control window that prevents the server from ever freeing the allocated memory.

A remote attacker can exploit this in Envoy's default HTTP/2 configuration to consume and hold large amounts of server memory (up to 32GB in approximately 20 seconds), rendering the server inaccessible.

This vulnerability exists in each server's default HTTP/2 configuration and requires no authentication to exploit.

External Reference: https://blog.calif.io/p/codex-discovered-a-hidden-http2-bomb