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

Source: https://junglewise.ai/threats/cve-2026-39835-go-x-crypto-ssh-denial-of-service-in-certchecker  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-22. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/golang-org-x-crypto), [golang.org/x/crypto/ssh (Go)](https://junglewise.ai/threats/technologies/golang-org-x-crypto-ssh). Vendors: [Go](https://junglewise.ai/threats/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

  ```sh
  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

- [https://go.dev/cl/781660](https://go.dev/cl/781660)
- [https://go.dev/issue/79563](https://go.dev/issue/79563)
- [https://groups.google.com/g/golang-announce/c/a082jnz-LvI](https://groups.google.com/g/golang-announce/c/a082jnz-LvI)
- [https://pkg.go.dev/vuln/GO-2026-5015](https://pkg.go.dev/vuln/GO-2026-5015)

## Related threats

- [Go SSH deadlock vulnerability in channel handling](https://junglewise.ai/threats/cve-2026-56855-go-ssh-deadlock-vulnerability-in-channel-handling)
- [Go x/crypto/ssh deadlock denial of service on undecided channel](https://junglewise.ai/threats/cve-2026-78662-go-2026-6354-prevent-dos-on-deadlocked-undecided-channel-in)
- [Go SSH source-address permission validation bypass in authentication callbacks](https://junglewise.ai/threats/cve-2026-56854-go-ssh-source-address-permission-validation-bypass-in)
- [GO-2026-5932 - The golang.org/x/crypto/openpgp package is unmaintained, unsafe by design, and has known security issues](https://junglewise.ai/threats/go-2026-5932-the-golang-org-x-crypto-openpgp-package-is-unmaintained-7e8ca4de)
- [Go x/crypto denial of service in SSH agent Ed25519 parsing](https://junglewise.ai/threats/cve-2026-46598-go-x-crypto-denial-of-service-in-ssh-agent-ed25519-parsing)