What is the CVSS score of EUVD-2026-31395?

EUVD-2026-31395 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.0%.

How to fix or mitigate EUVD-2026-31395?

Within 24 hours: Identify all systems and applications using Go x/crypto/ssh versions before 0.52.0 through dependency scanning and software inventory tools. Within 7 days: Upgrade all affected applications and services to Go x/crypto/ssh 0.52.0 or later and redeploy; prioritize SSH servers and authentication infrastructure. Within 30 days: Validate upgrades through security key authentication testing and review SSH key management policies for all privileged accounts.

golang.org/x/crypto/ssh EUVD-2026-31395

Q: Which versions of golang.org/x/crypto/ssh are affected by EUVD-2026-31395?

Go x/crypto/ssh versions before 0.52.0 fail to verify the User Presence flag in FIDO/U2F security key signatures, allowing SSH servers to accept signatures from stolen or relayed hardware tokens…. A patch is available.

| CVE-2026-39831 CRITICAL

Missing Authorization (CWE-862)

2026-05-22 Go

GHSA-89gr-r52h-f8rx

Authentication Bypass SSH Red Hat Golang Org X Crypto Ssh Golang Org X Crypto

9.1

CVSS 3.1 · Vendor: Go

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Compromise host with plugged-in FIDO key
Delivery

Invoke authenticator without touch or replay captured signature
Exploit

Connect to Go-based SSH server
Execution

Server's Verify() skips User Presence check
Persist

Authenticate as victim
Impact

Access shell or git/CI resources

Vulnerability Assessment

Weakness	CWE CWE-862 OWASP Top 10:2025 A01:2025 - Broken Access Control ASVS 5.0 V8 - Authorization Authorization checks on every request MITRE ATT&CK 1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Exploitation Conditions	The target server must be built against golang.org/x/crypto/ssh prior to 0.52.0, must run an SSH server using this library's verification path (not OpenSSH itself), and must accept FIDO/U2F key types sk-ecdsa-sha2-nistp256@openssh.com or sk-ssh-ed25519@openssh.com for authentication. The attacker must already possess a valid signature blob or have the ability to invoke the authenticator without touch - typically via local malware on a host where the security key is inserted, a hijacked ssh-agent forwarding session, or a captured/replayable signature - so although CVSS rates PR:N/UI:N, real-world abuse presupposes prior proximity to the victim's key material. Servers that do not accept sk-* algorithms, or clients (which are unaffected by the missing server-side check), are not exploitable.
Impact	Signals are mixed and worth disentangling. CVSS 9.1 (AV:N/AC:L/PR:N/UI:N/C:H/I:H/A:N) reflects that an attacker who possesses or can relay an attestation/signature blob can authenticate over the network without privileges or interaction, and SSVC backs this with 'Automatable: yes, Technical Impact: total.' However, EPSS is only 0.01% (2nd percentile), there is no KEV listing, and exploitation status is 'none' - consistent with a vulnerability that weakens a defense-in-depth control (the touch requirement) rather than providing direct unauthenticated RCE. Real-world risk is concentrated in environments that rely on FIDO touch as the sole barrier against signature reuse, malware on the workstation hosting the security key, or hijacked agent-forwarded sessions; for deployments that also require valid private keys or PINs, impact is meaningfully smaller than CVSS suggests. The CVSS A:N is consistent with this being an auth-bypass, not a DoS.
Exploit ScenarioDerived	An attacker who compromises an endpoint with a plugged-in FIDO security key, or who intercepts a previously generated sk-* SSH signature blob, replays or generates a signature with the User Presence flag cleared and authenticates to a Go-based SSH server (bastion, Git server, CI agent) as the legitimate user - bypassing the physical-touch guarantee the user believed was protecting them. No public exploit is identified at time of analysis, but the cryptographic mechanics are straightforward and SSVC marks the issue automatable.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.

Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Jun 02, 2026

Authentication bypass in the Go x/crypto/ssh library (versions before 0.52.0) allows SSH servers to accept FIDO/U2F security key signatures that were generated without the required physical user touch. The Verify() method for sk-ecdsa-sha2-nistp256@openssh.com and sk-ssh-ed25519@openssh.com key types failed to check the User Presence flag, enabling unattended use of stolen or relayed hardware-token signatures. No public exploit identified at time of analysis and EPSS is very low (0.01%), but SSVC rates technical impact as total with automatable exploitation.

RemediationAI

Vendor-released patch: golang.org/x/crypto v0.52.0. Update the module with 'go get golang.org/x/crypto@v0.52.0' (or higher) and rebuild and redeploy all SSH server binaries; the Go team's announcement at https://groups.google.com/g/golang-announce/c/a082jnz-LvI, issue tracker entry https://go.dev/issue/79566, and the fix CL https://go.dev/cl/781662 document the change. After upgrading, the library enforces user-presence by default; operators who legitimately enrolled no-touch FIDO credentials must explicitly opt back in by returning a 'no-touch-required' extension in Permissions.Extensions from their PublicKeyCallback, accepting the trade-off that those specific keys regain pre-patch behavior. If upgrading is blocked, a workable compensating control is to reject sk-ecdsa-sha2-nistp256@openssh.com and sk-ssh-ed25519@openssh.com algorithms in PublicKeyCallback and require traditional ed25519/ecdsa keys instead, at the cost of losing FIDO-backed SSH on those servers; further references at https://vuldb.com/vuln/365122 and https://pkg.go.dev/vuln/GO-2026-5019.

Affected VersionsENISA

golang.org/x/crypto/ssh 0 <0.52.0

Affected Packages

go golang.org/x/crypto fix: 0.52.0

go golang.org/x/crypto/ssh fix: 0.52.0

euvd golang_org_x_crypto_ssh fix: 0.52.0

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 3 packages in go, euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The vulnerability lives in golang.org/x/crypto/ssh, the Go ecosystem's primary SSH implementation used by countless server tools, CI runners, bastions, and DevOps utilities (Terraform providers, Kubernetes tooling, Drone, etc.). FIDO/U2F SSH key types defined by OpenSSH embed a flags byte in each signature; bit 0x01 (User Presence) attests that the user physically touched the authenticator. Per CWE-862 (Missing Authorization), the library's Verify() routine for the sk-* SSH algorithms decoded the signature blob but never enforced that this flag was set, so signatures forged or captured without touch passed validation. The fix in https://go.dev/cl/781662 introduces a default touch-required check, with an opt-out via a 'no-touch-required' extension returned from PublicKeyCallback for callers that intentionally provisioned no-touch credentials.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (Go) PRIMARY 9.1 CRITICAL

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

SUSE CRITICAL

Red Hat 8.1 HIGH

Primary rating from Vendor (Go).

CVSS VectorVendor: Go

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

CVSS changed

Jun 02, 2026 - 16:37 NVD

9.1 (None) 9.1 (CRITICAL)

Patch available

May 22, 2026 - 04:31 EUVD

CVE Published

May 22, 2026 - 02:31 nvd

UNKNOWN (no severity yet)

DescriptionCVE.org

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.

Executive ViewAI

Why It Matters

Go x/crypto/ssh versions before 0.52.0 fail to verify the User Presence flag in FIDO/U2F security key signatures, allowing SSH servers to accept signatures from stolen or relayed hardware tokens without physical user interaction. This authentication bypass undermines a core security property of hardware-based authentication across affected systems, risking unauthorized access if security keys are compromised. Vendor-released patch version 0.52.0 is available and requires immediate deployment.

Business Impact: High

Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score

0.0%

Top 98% exploitable

Threat Intel

1 sources

Data Quality

7 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

Vulnrichment GHSA MSRC Vendor

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity CRITICAL

CISA KEV No

Public POC No

EPSS 0.0%

Patch available Yes

Active threat No

Deciding rule

CRITICAL severity

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact

High

Technical Impact

Total

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +46

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

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Vendor StatusVendor

SUSE

Severity: Critical

Product	Status
openSUSE Leap 16.0	Fixed
openSUSE Tumbleweed	Fixed
SUSE Linux Enterprise Module for HPC 15 SP7	Affected
SUSE Linux Enterprise High Performance Computing 15 SP7	Affected
SUSE Linux Enterprise Server 15 SP6-LTSS	Affected

References

Advisories & patches

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