How severe is CVE-2026-39835?

CVE-2026-39835 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-39835?

CVE-2026-39835 affects the following packages: golang.org/x/crypto (Go). Ecosystems affected: Go.

How do I fix CVE-2026-39835?

Update golang.org/x/crypto to 0.52.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39835 is resolved across your whole dependency graph.

How do I detect CVE-2026-39835 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for golang.org/x/crypto, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-39835 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-39835 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-39835 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-39835?

CVE-2026-39835 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 42th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-39835?

CVE-2026-39835 is classified as CWE-295 (CWE-295), NULL Pointer Dereference (CWE-476). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-39835 published, and has it been updated?

CVE-2026-39835 was published on May 22, 2026 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2026-39835 — x/crypto

MEDIUM

CVE-2026-39835 is a medium-severity (CVSS 5.3) CWE-295 vulnerability in golang.org/x/crypto. A fix is available for golang.org/x/crypto — see the affected versions and patch details below.

Invoking server panic during CheckHostKey/Authenticate in golang.org/x/crypto/ssh

Also known asGHSA-78mq-xcr3-xm33GO-2026-5015

Published

May 22, 2026

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39835.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk-0.16%

Lower risk than most CVEs42th percentile — riskier than 42% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-39835 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹golang.org/x/crypto

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`golang.org/x/crypto`	all versions	0.52.0`go get golang.org/x/crypto@v0.52.0`

Affected Products

1 product · 1 configurations

Application

cryptogolang

< 0.52.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for golang.org/x/crypto, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update golang.org/x/crypto to 0.52.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39835 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This is an Important denial of service flaw in `golang.org/x/crypto/ssh` affecting SSH servers that utilize `CertChecker` as a public key callback without explicitly configuring `IsUserAuthority` or `IsHostAuthority`. A remote, unauthenticated attacker can trigger a server panic by presenting a specially crafted…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-39835 (CC BY 4.0)

Product	Fixed in	Advisory
Cryostat 4 on RHEL 9	`cryostat/cryostat-storage-rhel9:4.2.0-19`	RHSA-2026:48151
Red Hat Enterprise Linux 10	`buildah-2:1.43.1-3.el10_2`	RHSA-2026:36199
Red Hat Enterprise Linux 10	`podman-7:5.8.2-4.el10_2`	RHSA-2026:37072
Red Hat Enterprise Linux 8	`container-tools:rhel8-8100020260709093628.afee755d`	RHSA-2026:38504
Red Hat Enterprise Linux 9	`podman-6:5.8.2-4.el9_8`	RHSA-2026:37123
Red Hat Enterprise Linux 9	`buildah-2:1.43.1-3.el9_8`	RHSA-2026:37410
Red Hat OpenShift Container Platform 4.22	`openshift-0:4.22.0-202608010430.p2.g5f1e0e7.assembly.stream.el8`	RHSA-2026:51036
RHEM 1.0 for RHEL 9	`flightctl-0:1.0.3-1.el9em`	RHSA-2026:36796

Frequently Asked Questions

O3 Security · Impact-Aware SCA

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