How severe is CVE-2026-39831?

CVE-2026-39831 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-39831 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (40th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-39831?

CVE-2026-39831 affects Golang Crypto. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-39831?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-39831 have an EU (EUVD) identifier?

Yes. CVE-2026-39831 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31395.

When was CVE-2026-39831 published?

CVE-2026-39831 was published on 2026-05-22 and last updated on 2026-07-23.

CVE-2026-39831

Q: What is CVE-2026-39831?

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

CVE-2026-39831 is a critical-severity vulnerability in Golang Crypto with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-862.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (40th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-31395
Weakness: CWE-862
Affected product: Golang Crypto
Published: 2026-05-22
Last modified: 2026-07-23

Description

The Verify() method for FIDO/U2F security key types ([email protected], [email protected]) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

Frequently asked questions

What is CVE-2026-39831?: The Verify() method for FIDO/U2F security key types ([email protected], [email protected]) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.
How severe is CVE-2026-39831?: CVE-2026-39831 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-39831 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (40th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-39831?: CVE-2026-39831 affects Golang Crypto. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-39831?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-39831 have an EU (EUVD) identifier?: Yes. CVE-2026-39831 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-31395.
When was CVE-2026-39831 published?: CVE-2026-39831 was published on 2026-05-22 and last updated on 2026-07-23.

References

Affected products (1)

cpe:2.3:a:golang:crypto:*:*:*:*:*:go:*:*

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