CVE-2026-78662 Prevent DoS on deadlocked undecided channel in golang.org/x/crypto/ssh

High 7.5 Published 2 Sep 2026 Updated 3 Sep 2026

A malicious peer can cause a denial of service by flooding a deadlocked undecided channel in the Go SSH library.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-78662?

CVE-2026-78662 is a high-severity denial of service vulnerability in golang.org/x/crypto/ssh, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Previously, a channel registered in the mux's chanList is not usable until it is established. A malicious peer was able flood the channel's incomingRequests, deadlocking the entire connection. Now, we add an atomic established state, set when a channel becomes usable. Until such a time, handlePacket drops every packet other than the open confirmation/failure, without blocking and without tearing down the connection.

Weakness: CWE-770

Which versions are affected by CVE-2026-78662?

1 open source package ship an affected version, including golang.org/x/crypto. It affects 1 product.

Package	Affected	Fixed in
`golang.org/x/crypto` Go	All versions	`0.56.0`

Products include Golang Crypto.

How do I fix CVE-2026-78662?

Upgrade golang.org/x/crypto to 0.56.0 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-78662 being exploited?

There is no known exploitation of CVE-2026-78662 in the wild and no public exploit code.

Sources

Also known as AZL-99126, AZL-99129, AZL-99144, AZL-99156, AZL-99165, AZL-99195 and 1492 more.