PatchTheCVECVE-2026-39831: The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openss
CVE-2026-39831 is a critical-severity flaw (CVSS 9.1) affecting crypto. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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.
Why this priority
- Critical severity
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.1 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.5% (top 59%) |
| CISA exploited list | No |
| Weakness | CWE-862 |
| Published | 2026-05-22 |
| Last modified | 2026-07-23 |
Last updated 2026-07-23 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-39831?
crypto: upgrade to 0.52.0. Exact commands for each OS are on this page.
Is CVE-2026-39831 being exploited?
CVE-2026-39831 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-39831 affect?
CVE-2026-39831 affects crypto. Severity is critical (CVSS 9.1). 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
How urgent is CVE-2026-39831?
Priority 52/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist
Software pages
OpenSSH vulnerabilities · Go (Golang) vulnerabilities
Related CVEs
- CVE-2026-39835 MEDIUM 5.3 UPGRADE SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or IsHostAuthority
- CVE-2026-39830 CRITICAL 9.1 UPGRADE A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the
- CVE-2026-39829 HIGH 7.5 UPGRADE The RSA and DSA public key parsers did not enforce size limits on key parameters
- CVE-2026-42508 CRITICAL 9.1 UPGRADE Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation
- CVE-2026-39832 CRITICAL 9.1 UPGRADE When adding a key to a remote agent constraint extensions such as restrict-destination-v00@openssh.com were no