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CVE-2026-39831VulnerabilityPublished Updated

Lxd: The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com

Affects lxdSource GCVE Database

0
Authoritative record:CVE-2026-39831· Critical 9.1

Not known to be exploited · CVSS 9.1 Critical · fixed in 20240716.00-0ubuntu1~16.04.0+esm3 : patch lxd as a priority.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score
9.1Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 20240716.00-0ubuntu1~16.04.0+esm3, 20241011.01-0ubuntu1~18.04.0+esm3, 20250116.00-0ubuntu1~20.04.0+esm3 +8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 22 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Ubuntu 26.10snapdpkg:deb/ubuntu/snapd?arch=source&distro=stonkingOther threatsAffected
  • 2.74.1+ubuntu26.04.4 – 2.77.1+ubuntu26.10.1
5 affected builds
Fixed in–
Ubuntu 26.04 LTSgoogle-guest-agentpkg:deb/ubuntu/google-guest-agent?arch=source&distro=resoluteOther threatsAffected
  • <20250506.01-0ubuntu2.1
Fixed in
  • 20250506.01-0ubuntu2.1
Ubuntu 26.04 LTSsnapdpkg:deb/ubuntu/snapd?arch=source&distro=resoluteOther threatsAffected
  • 2.71.1+ubuntu25.10.1 – 2.77.1+ubuntu26.04.2
12 affected builds
Fixed in–
Ubuntu Pro 26.04 LTSgolang-go.cryptopkg:deb/ubuntu/golang-go.crypto?arch=source&distro=esm-apps/resoluteOther threatsAffected
  • <1:0.47.0-1ubuntu0.1~esm1
Fixed in
  • 1:0.47.0-1ubuntu0.1~esm1
Ubuntu 25.10golang-go.cryptopkg:deb/ubuntu/golang-go.crypto?arch=source&distro=questingOther threatsAffected
  • =1:0.25.0-1
  • =1:0.25.0-1ubuntu0.1
Fixed in–
Ubuntu 25.10google-guest-agentpkg:deb/ubuntu/google-guest-agent?arch=source&distro=questingOther threatsAffected
  • <20250506.01-0ubuntu1.2
Fixed in
  • 20250506.01-0ubuntu1.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

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.

References

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