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LxdApplication · Canonical

CVE-2023-49721

MEDIUM · 6.7 CVSS v3.1 Published 2024-02-14
Fix available
A fix is available. Upgrade to 5.21.0 or later.
See remediation →
69/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An insecure default to allow UEFI Shell in EDK2 was left enabled in LXD. This allows an OS-resident attacker to bypass Secure Boot.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

LXD ships with an insecure default configuration that enables the UEFI Shell in EDK2 firmware. Since the UEFI Shell provides an interactive command environment accessible at boot time, an attacker with OS-level code execution can leverage it to bypass Secure Boot protections and execute arbitrary unsigned code during the boot process.

MitigationDisable UEFI Shell in EDK2 via LXD configuration or update to a patched LXD version that disables this feature by default, then verify Secure Boot remains enforced.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
LxdApplication
Affected:>= 5.0.0, < 5.21.0
Edk2Application
Affected:<= 2023.11-8

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed LXD version
    Run 'lxd --version' or 'snap list lxd' to determine the installed version
    Affected if Version is >= 5.0.0 and < 5.21.0
  2. Identify LXD instances using UEFI firmware
    List LXD instances and inspect their configuration for firmware type using 'lxc config show <instance>' and checking for 'firmware' or 'uefi' settings
    Affected if Instances are configured to use UEFI firmware (OVMF/EDK2)
  3. Verify UEFI Shell is enabled in EDK2 configuration
    Inspect the EDK2 config file or LXD profile for the UEFI Shell setting. In LXD profiles this may appear under 'security.cpu.nesting' or firmware-related config keys, or in the OVMF/EDK2 varstore file
    Affected if UEFI Shell is explicitly enabled or not disabled in the firmware configuration
  4. Confirm reliance on Secure Boot protection
    Check if LXD instances have Secure Boot enforcement enabled via 'lxc config get <instance> security.secureboot' or similar configuration keys
    Affected if Secure Boot is enabled and enforced on the instances

You are affected if you run LXD version 5.0.0 through 5.20.x with UEFI-enabled instances where the UEFI Shell remains enabled in the EDK2 configuration and you rely on Secure Boot for boot integrity.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.21.0 or later
Fixed in 5.21.0
Interim mitigation

Disable UEFI Shell in EDK2 via LXD configuration or update to a patched LXD version that disables this feature by default, then verify Secure Boot remains enforced.

Recommended fix High confidence

LXD 5.21.0 or later

  1. Check current LXD version using: lxd version
  2. Upgrade LXD to version 5.21.0 or later. For snap installations, run: sudo snap refresh lxd --channel=5.21/stable or a later stable channel
  3. For non-snap installations, follow your distribution's package upgrade procedure to obtain LXD 5.21.0 or newer
  4. After upgrade, verify the LXD version is >= 5.21.0 using: lxd version
  5. If using custom EDK2 builds, ensure the OVMF package is also updated to a version that disables UEFI Shell by default
Caveat Minor: If existing workloads relied on UEFI Shell being accessible, they will need to be reconfigured to use a custom EDK2 build with Shell enabled if truly needed

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Lxd Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-49721 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data