CVE-2026-39834 Invoking infinite loop on large channel writes in golang.org/x/crypto/ssh

Critical 9.1 Published 22 May 2026 Updated 22 May 2026

An attacker can cause a denial of service by triggering an infinite loop via large SSH channel writes due to an integer overflow.

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

What is CVE-2026-39834?

CVE-2026-39834 is a critical 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

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

Weakness: CWE-190

Which versions are affected by CVE-2026-39834?

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-2026-39834?

Upgrade golang.org/x/crypto to 0.52.0 or later.

Is CVE-2026-39834 being exploited?

There is no known exploitation of CVE-2026-39834 in the wild and no public exploit code.

Sources

Also known as AZL-87203, AZL-87233, AZL-87302, AZL-87423, AZL-87441, AZL-87648 and 1132 more.