Is CVE-2026-39835 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-39835 being exploited in the wild.

How severe is CVE-2026-39835?

Medium severity, with a CVSS score of 5.3, 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-2026-39835?

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-2026-39835 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-39835?

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.

CVE-2026-39835: Go x/crypto/ssh denial of service in CertChecker

Q: Is there a fix for CVE-2026-39835?

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.

Q: How is CVE-2026-39835 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-39835?

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.

CVE-2026-39835 · Severity: medium · CVSS 5.3 · Published 2026-05-22

A vulnerability in the Go SSH library can allow a remote attacker to crash an SSH server. This occurs when the server is configured to use a specific certificate checking component without certain security settings enabled. An exploit would result in a denial-of-service, making the SSH service unavailable to legitimate users.

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

Quick answers

Is CVE-2026-39835 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-39835 being exploited in the wild.
How severe is CVE-2026-39835?: Medium severity, with a CVSS score of 5.3, 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-2026-39835?: 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-2026-39835 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-39835?: 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 panic (crash) exists in the golang.org/x/crypto/ssh package within the CertChecker.Authenticate and CertChecker.CheckHostKey flows. The issue occurs when CertChecker is used as a public key callback but the IsUserAuthority or IsHostAuthority fields are left as nil. A remote, unauthenticated attacker can trigger this panic by presenting a certificate during the handshake, leading to a denial-of-service. The fix, introduced in version 0.52.0, ensures that CertChecker returns an error instead of panicking when these callbacks are not configured.

Affected products

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

Identifiers

CVE-2026-39835
GHSA-78mq-xcr3-xm33
GO-2026-5015

Timeline

2026-05-22: disclosed: NVD publication date
2026-06-25: advisory: GitHub Advisory published

References

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