CVE-2026-39830 Invoking client can cause server deadlock on unexpected responses in golang.org/x/crypto/ssh

Critical 9.1 Published 22 May 2026 Updated 18 Sep 2026

A malicious SSH peer can cause a server deadlock and resource leak by sending unsolicited global request responses, requiring a patch to 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-2026-39830?

CVE-2026-39830 is a critical denial of service vulnerability in golang.org/x/crypto/ssh, published on 22 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.

Weakness: CWE-772, CWE-119

Which versions are affected by CVE-2026-39830?

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

Package	Affected	Fixed in
`golang.org/x/crypto` Go	All versions	`0.52.0`
`golang.org/x/crypto` Go	All versions	`0.52.0`
`golang.org/x/crypto` Go	All versions	`0.52.0`

Products include Golang Crypto.

How do I fix CVE-2026-39830?

Upgrade golang.org/x/crypto to 0.52.0 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-2026-39830 being exploited?

There is no known exploitation of CVE-2026-39830 in the wild and no public exploit code.

Sources

Also known as AZL-87182, AZL-87236, AZL-87311, AZL-87399, AZL-87453, AZL-87633 and 1130 more.