openSUSE Leap 15.5 — grub2 — multiple vulnerabilities (2 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: SUSE advisory SUSE-IU-2023:774-1 (see also SUSE bugzilla)

Related CVEs: CVE-2023-4692 CVE-2023-4693

Upstream summary: An out-of-bounds write flaw was found in grub2's NTFS filesystem driver. This issue may allow an attacker to present a specially crafted NTFS filesystem image, leading to grub's heap metadata corruption. In some circumstances, the attack may also corrupt the UEFI firmware heap metadata. As a result, arbitrary code execution and secure boot protection bypass may be achieved.

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

A flaw in grub2 sits underneath every process on the host: local privilege escalation to root, container escape from an unprivileged namespace, memory corruption reachable from a crafted packet, or — in microcode, firmware and bootloader components — a weakness below openSUSE Leap 15.5 entirely. The update only stages files on disk: kernel and initramfs in /boot, blobs under /lib/firmware. The vulnerable code stays resident until the host boots it, which is why a package-database scan calls a host patched while it still runs the flaw. grub2 is boot-time code — kernel, modules, device firmware, microcode or bootloader — not a service, so there is no unit to restart; only a reboot (or a livepatch, where one applies) loads the new build.

Environment & Reproduction

Reproduction targets openSUSE Leap 15.5. Confirm release and installed package:

cat /etc/os-release
rpm -q grub2
zypper info grub2 | head -20
zypper lr -E                              # enabled repositories
SUSEConnect --status-text 2>/dev/null || echo 'SCC not connected (optional on openSUSE Leap)'

Exercise the workload that uses grub2 while collecting:

sudo zypper needs-rebooting; echo "exit=$?"  # SLE15 SP1 / Leap 15.1+ / Tumbleweed: exit 102 (ZYPPER_EXIT_INF_REBOOT_NEEDED) = reboot required, exit 0 = not required
ls -l /run/reboot-needed /var/run/reboot-needed 2>/dev/null  # marker file left by an earlier zypper transaction (path varies by release); 'zypper needs-rebooting' is the authoritative check
sudo journalctl -xe --no-pager | tail -200
sudo tail -200 /var/log/zypp/history
sudo journalctl -k | grep -i apparmor | tail -100
# Bundle evidence for SUSE / community support:
sudo supportconfig -R /var/tmp -B grub2

Root Cause Analysis

Root cause is documented in SUSE advisory SUSE-IU-2023:774-1. openSUSE security maintainers shipped fixes in the corresponding grub2 update for openSUSE Leap 15.5; running an outdated build leaves the host exposed to the failure modes described in the advisory. Correlate zypper history with system logs:

sudo zypper history | grep grub2
sudo zypper history --since='-7 days' | tail -40
sudo journalctl -k | grep -i apparmor | tail -100
cat /proc/sys/kernel/tainted   # non-zero = tainted kernel / out-of-tree modules

Quick Triage

Run these on openSUSE Leap 15.5 to capture the current state of grub2:

rpm -q grub2                              # installed NVR
rpm -V grub2                              # verify shipped files
sudo zypper patch-check                    # open patches
sudo zypper lp 2>/dev/null | head
systemctl --failed --no-pager
sudo firewall-cmd --list-all
sudo aa-status                             # AppArmor profiles
rpm -ql grub2 | grep -E '^/(usr/lib|etc)/systemd/(system|user)/[^/]+\.(service|socket|timer|path|target|mount)$'  # the units grub2 REALLY ships - NO OUTPUT means it ships no service at all, so never run systemctl on it
rpm -ql grub2 | grep -E '^/usr/sbin/rc[^/]+$'  # SUSE-only rcNAME compat symlink (it points at /usr/sbin/service, not at a unit): the NAME after 'rc' IS the service name - bind ships /usr/sbin/rcnamed, so the unit is named.service

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

2. Tail the journal for grub2 and the system bus.

   sudo journalctl -xe -f --no-pager

3. Inspect firewall posture (firewalld is the default on openSUSE).

   sudo firewall-cmd --list-all-zones --permanent
   sudo nft list ruleset 2>/dev/null | head -50

4. Surface AppArmor denials and switch the profile to complain mode if needed.

   sudo journalctl -k | grep -i 'apparmor="DENIED"' | tail -30
   sudo aa-status

5. Verify grub2 integrity and reinstall if anything is altered.

   sudo rpm -V grub2
   sudo zypper verify
   sudo zypper install --force grub2

6. Inspect Snapper snapshots to know exactly which transaction introduced the regression.

   sudo snapper list | tail -20
   sudo snapper status <pre-id>..<post-id>

7. Correlate findings with /var/log/zypp/history, zypper history, and SUSE advisory SUSE-IU-2023:774-1 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective zypper transaction referenced by SUSE advisory SUSE-IU-2023:774-1, then reload affected systemd units:

sudo zypper ref                        # refresh repos
sudo zypper -n patch                   # apply ALL open patches (recommended)
# Or target a single package:
sudo zypper -n update grub2
# Unit name may differ from pkg name; check first:
rpm -q grub2                           # confirm new NVR

For kernel / glibc / systemd / openssl advisories a reboot is required. Snapper takes pre/post snapshots on Btrfs root automatically, giving a safety net:

sudo zypper ps -s                      # services using deleted libs
sudo snapper list | tail -5            # pre/post snapshots around the patch
sudo systemctl reboot                  # or: sudo shutdown -r now

Solution – Alternative Approaches

If the primary fix is not viable, choose from these:

• Roll back via Snapper (Btrfs snapshots are taken automatically before zypper transactions on openSUSE Leap 15.5). This is the primary safety net for openSUSE administrators:

  sudo snapper list
  sudo snapper status <pre-id>..<post-id>   # diff between two snapshot numbers
  sudo snapper undochange <pre-id>..<post-id>
  sudo snapper rollback <pre-id>            # boot the host into the chosen snapshot
  sudo systemctl reboot

• Lock the package so zypper cannot upgrade it:

  sudo zypper al grub2                   # add lock
  zypper ll | grep grub2                 # list locks
  sudo zypper rl grub2                   # remove lock

• Install an older NVR if a regression is suspected:

  zypper se -s grub2                     # show all available versions
  sudo zypper install --oldpackage grub2-<older-NVR>

• Disable the AppArmor profile briefly to confirm policy is the cause, then re-enable:

  # reproduce, capture denials in the journal:
  sudo journalctl -k | grep apparmor | tail

• openSUSE Leap follows the SUSE Linux Enterprise patch stream. Sync against the official update repository if a mirror has drifted:

  sudo zypper mr -e repo-update          # ensure update repo is enabled
  sudo zypper ref repo-update
  sudo zypper -n patch

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q grub2                                            # expected fixed NVR
sudo zypper patch-check                                  # 0 critical patches outstanding
sudo firewall-cmd --list-services
sudo aa-status | head -5
sudo zypper ps -s                                        # any services still using deleted libs

The conditions described in the advisory must no longer be reported for grub2 across two consecutive runs.

Rollback Plan

Capture state before any change. On openSUSE, Snapper is the canonical rollback path:

rpm -qa > /root/rpm-pre.txt
sudo zypper history list > /root/zypper-history-pre.txt
# Snapper takes pre/post snapshots automatically on Btrfs root.
sudo snapper create -d 'pre-patch-grub2'   # explicit named snapshot
sudo snapper list | head

To revert if the patch / roll is bad:

# Preferred on Btrfs root — boot the prior snapshot:
sudo snapper list
sudo snapper rollback <pre-id>
sudo systemctl reboot
# Or downgrade just the package:
sudo zypper install --oldpackage grub2-<older-NVR>
# Custom AppArmor profile cleanup:

Prevention & Hardening

Reduce the chance of this recurring on openSUSE Leap 15.5:

• Enable automatic patch installation:

  sudo zypper install -y zypper-automatic
  sudo systemctl enable --now zypper-automatic.timer
  # Or use YaST: yast2 online_update_configuration

• Subscribe to opensuse-security-announce and watch suse.com/support/update.

• Lock sensitive packages so they cannot be auto-upgraded:

  sudo zypper al grub2

• Ensure Snapper is enabled on the root subvolume and pre/post hooks run for every zypper transaction. This is the cornerstone of safe openSUSE patching:

  sudo snapper -c root get-config | head
  # Default zypper plugin: /usr/lib/zypp/plugins/commit/snapper.zypp-commit-plugin
  sudo snapper list | tail -10

• Monitor file integrity with AIDE:

  sudo zypper install -y aide
  sudo aide --init && sudo mv /var/lib/aide/aide.db.new /var/lib/aide/aide.db
  sudo aide --check

• Keep AppArmor profiles in enforce; review /etc/apparmor.d/ after every package upgrade.

• Apply CIS / openSUSE hardening guidance and use salt or ansible to enforce baseline state across the fleet.

Related Errors & Cross-Refs

Issues that commonly surface alongside a grub2 update: zypper lock contention, systemd unit ordering cycles, AppArmor denials, firewalld zone drift, and kernel taint flags. Useful triage:

sudo zypper ps -s
systemd-analyze critical-chain
sudo journalctl -k | grep apparmor | tail
sudo firewall-cmd --get-active-zones
cat /proc/sys/kernel/tainted
sudo snapper list | tail

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References & Further Reading

Primary reference: SUSE advisory SUSE-IU-2023:774-1 (see also SUSE bugzilla). Manual pages useful on openSUSE Leap 15.5:

man zypper
man zypper.conf
man systemctl
man journalctl
man firewall-cmd
man snapper
man apparmor
man aa-status

Other resources: openSUSE documentation, suse.com/security, openSUSE security portal, and per-package notes in /usr/share/doc/packages/grub2/ for components implicated in this advisory.

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