CVE-2026-78660

Summary

This vulnerability allows HTTP/2 implementations to forward malformed framing headers to HTTP/1 clients when acting as a reverse proxy, potentially enabling response smuggling attacks. The flaw occurs because HTTP/2 handling was too permissive with malformed headers that don't affect HTTP/2 framing but can interfere with HTTP/1 processing.

Exploitability

Exploitation requires a specific chain involving an HTTP/2 reverse proxy forwarding to an HTTP/1 client, with both sides having lax header validation, making it moderately difficult to exploit without specific conditions.

Blast radius

The impact is limited to environments using HTTP/2 reverse proxies that forward responses to HTTP/1 clients, potentially allowing attackers to smuggle responses and bypass security controls in vulnerable configurations.

Detection

No reliable host or network indicator is derivable from the published description.

Prioritized remediation

Upgrade to version 2.590 or later to fix the malformed header handling in HTTP/2 implementation.

Analysis generated locally by garnet-coder (no data left the box). AI-assisted — verify against primary sources before acting.