CVE-2026-39831: CWE-290: Authentication Bypass by Spoofing in golang.org/x/crypto golang.org/x/crypto/ssh
A critical authentication bypass vulnerability (CVE-2026-39831) exists in golang.org/x/crypto/ssh affecting FIDO/U2F security key types. The Verify() method fails to check the User Presence flag, allowing signatures generated without physical user interaction to be accepted. This flaw enables unauthorized use of hardware security keys without user touch unless mitigated by a specific extension in Permissions.Extensions. The vulnerability has a high CVSS score of 9.1 and impacts authentication security.
AI Analysis
Technical Summary
CVE-2026-39831 is an authentication bypass vulnerability in the golang.org/x/crypto/ssh package related to FIDO/U2F security keys. The Verify() method does not verify the User Presence flag, which is intended to ensure that a physical user touch occurred during signature generation. As a result, signatures created without user presence are accepted, allowing potential unauthorized use of hardware security keys. Mitigation is possible by returning a specific extension in Permissions.Extensions, but no official patch or remediation level has been disclosed at this time.
Potential Impact
This vulnerability allows attackers to bypass authentication mechanisms relying on FIDO/U2F security keys by accepting signatures generated without physical user presence. This undermines the security guarantees of hardware security keys, potentially enabling unauthorized access without user interaction. The CVSS score of 9.1 reflects a critical impact on confidentiality and integrity with no required privileges or user interaction.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Mitigation can be applied by returning a specific extension in Permissions.Extensions to enforce user presence checks. Until an official fix is available, implement this mitigation if possible. Monitor vendor communications for updates on patches or official fixes.
CVE-2026-39831: CWE-290: Authentication Bypass by Spoofing in golang.org/x/crypto golang.org/x/crypto/ssh
Description
A critical authentication bypass vulnerability (CVE-2026-39831) exists in golang.org/x/crypto/ssh affecting FIDO/U2F security key types. The Verify() method fails to check the User Presence flag, allowing signatures generated without physical user interaction to be accepted. This flaw enables unauthorized use of hardware security keys without user touch unless mitigated by a specific extension in Permissions.Extensions. The vulnerability has a high CVSS score of 9.1 and impacts authentication security.
CVSS v3.1
Score 9.1critical
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-39831 is an authentication bypass vulnerability in the golang.org/x/crypto/ssh package related to FIDO/U2F security keys. The Verify() method does not verify the User Presence flag, which is intended to ensure that a physical user touch occurred during signature generation. As a result, signatures created without user presence are accepted, allowing potential unauthorized use of hardware security keys. Mitigation is possible by returning a specific extension in Permissions.Extensions, but no official patch or remediation level has been disclosed at this time.
Potential Impact
This vulnerability allows attackers to bypass authentication mechanisms relying on FIDO/U2F security keys by accepting signatures generated without physical user presence. This undermines the security guarantees of hardware security keys, potentially enabling unauthorized access without user interaction. The CVSS score of 9.1 reflects a critical impact on confidentiality and integrity with no required privileges or user interaction.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Mitigation can be applied by returning a specific extension in Permissions.Extensions to enforce user presence checks. Until an official fix is available, implement this mitigation if possible. Monitor vendor communications for updates on patches or official fixes.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Go
- Date Reserved
- 2026-04-07T18:13:03.528Z
- Cvss Version
- null
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a0fcdabe1370fbb487d5010
Added to database: 05/22/2026, 03:29:47 UTC
Last enriched: 07/08/2026, 13:55:13 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 58
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