CVE-2026-39835: Invoking server panic during CheckHostKey/Authenticate in golang.org/x/crypto/ssh

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-22 · updated 2026-09-18
Weakness: CWE-295

Description

SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or IsHostAuthority could be caused to panic by a client presenting a certificate. CertChecker now returns an error instead of panicking when these callbacks are nil.

Affected products

golang.org/x/crypto/ssh: before 0.52.0 — fixed in 0.52.0
Golang.Org/X/Crypto: before 0.52.0 — fixed in 0.52.0

How to fix

Upgrade to a fixed version: golang.org/x/crypto/ssh 0.52.0; Golang.Org/X/Crypto 0.52.0. Check the vendor advisory for mitigations.

References

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