CVE-2026-39835: crypto Cert Validation Flaw — Fix

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.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0021

Probability of exploitation

0.11%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-295 CWE-295

Affected Products

Vendor	Product	Versions
golang	crypto	< 0.52.0

References

Advisories & Patches

https://pkg.go.dev/vuln/GO-2026-5015

Other References

https://go.dev/cl/781660 https://go.dev/issue/79563 https://groups.google.com/g/golang-announce/c/a082jnz-LvI

Frequently Asked Questions

What is CVE-2026-39835? +

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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-39835? +

CVE-2026-39835 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0021, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-39835? +

CVE-2026-39835 affects products from golang, specifically: crypto. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-39835? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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