CVE-2026-39830: Go x/crypto/ssh resource leak via unsolicited global request responses

CVE-2026-39830 · Severity: critical · CVSS 9.1 · Published 2026-05-22

A vulnerability in the Go SSH library could allow a malicious user to cause a server to stop responding or leak system resources. By sending unexpected messages, an attacker can block the server's ability to process connections, potentially leading to a complete service outage. This affects any Go-based application or service that uses this library to handle SSH connections.

Technologies: golang.org/x/crypto (Go), golang.org/x/crypto/ssh (Go). Vendors: Go.

Quick answers

Is CVE-2026-39830 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-39830 being exploited in the wild.
How severe is CVE-2026-39830?
Critical severity, with a CVSS score of 9.1, published 22 May 2026.
Which products and versions are affected?
golang.org/x/crypto (Go) SEMVER:introduced=0,fixed=0.52.0; golang.org/x/crypto/ssh (Go) < 0.52.0.
Is there a fix for CVE-2026-39830?
Yes. golang.org/x/crypto (Go): upgrade to 0.52.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-39830 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-39830?
Check whether you run golang.org/x/crypto (Go) or golang.org/x/crypto/ssh (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • golang.org/x/crypto (Go): upgrade to 0.52.0 or later
    go get golang.org/x/crypto@v0.52.0

Technical details

A vulnerability in the golang.org/x/crypto/ssh package allows a malicious SSH peer to trigger a deadlock in the connection's read loop. By sending unsolicited global request responses, an attacker can fill an internal buffer, blocking the associated goroutine. This blocked state cannot be recovered by calling Close(), leading to a persistent resource leak and potential denial of service for the server. The issue is rooted in improper handling of unexpected global responses, which are now discarded in patched versions. The vulnerability is reachable over the network without authentication.

Affected products

  • Go Project golang.org/x/crypto/ssh < 0.52.0

Identifiers

  • CVE-2026-39830
  • GHSA-vgwf-h737-ff37
  • GO-2026-5017

Timeline

  • 2026-05-21: other: Issue reported by NCC Group Cryptography Services
  • 2026-05-22: disclosed: NVD publication date
  • 2026-06-25: advisory: GitHub Advisory published

References

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