Ubuntu alert USN-8447-2 (lxd)

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[USN-8447-2] LXD vulnerabilities
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Thu, 18 Jun 2026 20:31:04 +0000
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==========================================================================
Ubuntu Security Notice USN-8447-2
June 18, 2026

lxd vulnerabilities
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in LXD.

Software Description:
- lxd: Container hypervisor based on LXC

Details:

USN-8447-1 fixed vulnerabilities in Go Cryptography. This update provides
the corresponding updates for Go Cryptography code embedded in LXD for
CVE-2026-39830, CVE-2026-39833, CVE-2026-39834, and CVE-2026-42508.

Original advisory details:

 It was discovered that Go Cryptography did not properly handle SSH global
 request responses. A remote attacker could possibly use this issue to cause
 a denial of service. (CVE-2026-39830)

 It was discovered that Go Cryptography did not properly verify user
 presence when using FIDO/U2F security keys. An attacker could possibly use
 this issue to bypass user presence verification for hardware security keys.
 This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04
 LTS, and Ubuntu 26.04 LTS. (CVE-2026-39831)

 It was discovered that Go Cryptography did not properly serialize SSH agent
 key constraint extensions. An attacker could possibly use this issue to
 bypass intended key usage restrictions. This issue only affected Ubuntu
 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS.
 (CVE-2026-39832)

 It was discovered that Go Cryptography did not properly enforce the
 confirm-before-use constraint in the SSH agent keyring. An attacker could
 possibly use this issue to use SSH keys without the required user
 confirmation. (CVE-2026-39833)

 It was discovered that Go Cryptography had an integer overflow when
 handling large SSH channel writes. A remote attacker could possibly use
 this issue to cause a denial of service. (CVE-2026-39834)

 It was discovered that Go Cryptography did not properly check certificate
 authority key revocation. An attacker could possibly use this issue to
 bypass certificate authority revocation checks. This issue only affected
 Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and
 Ubuntu 26.04 LTS. (CVE-2026-42508)

 It was discovered that Go Cryptography did not properly enforce the source-
 address critical option for all SSH server callback types. An attacker
 could possibly use this issue to bypass source address authorization
 restrictions. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-46595)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS
  lxd                             3.0.3-0ubuntu1~18.04.2+esm3
                                  Available with Ubuntu Pro

Ubuntu 16.04 LTS
  lxd                             2.0.11-0ubuntu1~16.04.4+esm3
                                  Available with Ubuntu Pro

In general, a standard system update will make all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-8447-2
  https://ubuntu.com/security/notices/USN-8447-1
  CVE-2026-39830, CVE-2026-39833, CVE-2026-39834, CVE-2026-42508


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