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LxdApplication · Canonical

CVE-2023-48733

MEDIUM · 6.7 CVSS v3.1 Published 2024-02-14
Fix available
A fix is available. Upgrade to after 2023.11-8 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 Ubuntu's EDK2. 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

Ubuntu's EDK2 firmware implementation contains an insecure default configuration that leaves the UEFI Shell enabled. This allows an attacker with OS-level privileges to execute the UEFI Shell and potentially bypass Secure Boot protections by modifying boot variables or executing unsigned code at the firmware level.

MitigationDisable UEFI Shell in UEFI/BIOS settings or update EDK2 to a version that disables the UEFI Shell by default. Verify Secure Boot is properly enabled and configured.

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= 5.21
Debian LinuxOperating system
Affected:= 10.0
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. Identify the EDK2 firmware version
    Check the EDK2 version by reading /sys/firmware/efi/fw_version or using 'dmidecode -s bios-version' if available. On Ubuntu/Debian systems, also check /usr/share/edk2/ovmf/ or similar firmware package directories for version files.
    Affected if The installed EDK2 version is 2023.11-8 or earlier (for Tianocore Edk2), or if running Canonical LXD versions 5.0 or 5.21 specifically.
  2. Locate UEFI Shell binary on the system
    Search for shell.efi or Shell.efi in the EFI System Partition: 'find /boot/efi -iname "*shell*.efi"' or mount the ESP partition and look in /efi/ and /efi/tools/ directories.
    Affected if A UEFI Shell binary (shell.efi) exists in any accessible EFI directory, indicating the shell may be available for execution.
  3. Check UEFI Boot Manager for Shell entry
    Run 'efibootmgr -v' to list all UEFI boot entries. Look for entries named 'UEFI Shell', 'Shell', or similar that point to shell.efi.
    Affected if A boot entry for UEFI Shell appears in the boot manager list, meaning it can be launched at boot time.
  4. Verify Secure Boot status
    Check if Secure Boot is enabled by running 'mokutil --sb-state' or checking '/sys/firmware/efi/secureboot' status. Also verify with 'bootctl status' if available.
    Affected if Secure Boot is disabled or not properly configured (mokutil shows 'Secure Boot disabled' or the secureboot file shows 0).

The environment is affected if UEFI Shell is present/enabled (shell.efi found or Shell boot entry exists) AND Secure Boot is disabled or not properly enforced, particularly on systems with vulnerable EDK2 versions or the specified LXD versions.

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 a release after 2023.11-8
Interim mitigation

Disable UEFI Shell in UEFI/BIOS settings or update EDK2 to a version that disables the UEFI Shell by default. Verify Secure Boot is properly enabled and configured.

Recommended fix Moderate confidence

EDK2 version greater than 2023.11-8 (or system vendor-specific UEFI firmware update containing the fix)

  1. Identify the EDK2/UEFI firmware version currently installed on affected systems
  2. Obtain and apply the latest EDK2 firmware update from the system vendor (OEM/ODM) or Ubuntu security repositories
  3. Verify that the UEFI Shell is disabled in the firmware settings after update
  4. Ensure Secure Boot is enabled in UEFI settings post-update
  5. Confirm the UEFI firmware version reflects the patched release (greater than 2023.11-8)
Caveat UEFI firmware updates carry risk of system unbootability if interrupted or incompatible; ensure backups and recovery options are available

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

Fix this in Lxd Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2023-48733 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
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