CVE-2026-78660: HTTP/2 transport accepts malformed framing-related headers in net/http

Description

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

High

Availability

None

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.4% · higher than 37% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

GO

golang.org/x/net/http2 · golang.org/x/net

before 0.60.0 · source: vendor

NE

net/http · Go standard library

before 1.26.9 · source: vendor

NE

net/http/internal/http2 · Go standard library

1.27.0-0 before 1.27.2 · source: vendor