CVE-2026-78660 HTTP/2 transport accepts malformed framing-related headers in net/http
Attackers can exploit response smuggling in Go's HTTP/2 reverse proxy by sending malformed headers, potentially compromising data integrity and confidentiality.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-78660?
CVE-2026-78660 is a high-severity vulnerability in golang.org/x/net/http2, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-444
Which versions are affected by CVE-2026-78660?
4 open source packages ship an affected version, including stdlib, golang and golang.org/x/net.
| Package | Affected | Fixed in |
|---|---|---|
stdlib Go | All versions | 1.26.9 |
stdlib Go | From 1.27.0-0 | 1.27.2 |
golang Bitnami | All versions | 1.26.9, 1.27.2 |
golang.org/x/net Go | All versions | 0.60.0 |
Linux distribution packages (1)
prometheus-ha_cluster_exporter openSUSE:Tumbleweed | All versions | 1.4.3-1.1 |
How do I fix CVE-2026-78660?
Upgrade stdlib to a fixed version for your release line: 1.26.9 or 1.27.2.
Is CVE-2026-78660 being exploited?
There is no known exploitation of CVE-2026-78660 in the wild and no public exploit code.
Sources
Also known as AZL-107033, AZL-107036, AZL-107054, AZL-107096, AZL-107105, AZL-107141 and 1101 more.