All vulnerabilities
CVE-2026-78660

HTTP/2 transport accepts malformed framing-related headers in net/http

Go standard library net/http
Open in ThreatlineRecord JSON
CVSS
7.5High
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.30%Chance of exploitation activity in the next 30 days, higher than 21% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in1.26.9Also 1.27.2, 0.60.0CVE List
Published8 Oct 2026Updated 9 Oct 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

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.

Text from CVE List

Affected versions 3

  • net/httpaffected: all versions before 1.26.9CVE List
  • net/http/internal/http2affected: 1.27.0-0 before 1.27.2CVE List
  • golang.org/x/net/http2affected: all versions before 0.60.0CVE List

References 5