CVE-2026-78660: Go Standard Library Net/http

High severity, CVSS 7.5. EPSS: 0.3% chance of exploitation in the next 30 days.

Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such headers to an HTTP/1 client when acting as a reverse proxy. If the HTTP/1 client also does not behave strictly enough, this can result in response smuggling.

Affected products

• Go Standard Library Net/http: before 1.26.9 (fixed in 1.26.9)
• Go Standard Library net/http/internal/http2: from 1.27.0-0, before 1.27.2 (fixed in 1.27.2)
• Golang.org/x/net golang.org/x/net/http2: before 0.60.0 (fixed in 0.60.0)

Published 2026-10-08. Last modified 2026-10-09.