SLES 15 — tboot — vulnerability — patch and remediation guide

📖 ~4 min read  •  Source: SUSE advisory SUSE-SU-2017:3090-1 (see also SUSE bugzilla)

Related CVEs: CVE-2017-16837

Upstream summary: Certain function pointers in Trusted Boot (tboot) through 1.9.6 are not validated and can cause arbitrary code execution, which allows local users to overwrite dynamic PCRs of Trusted Platform Module (TPM) by hooking these function pointers.

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 tboot 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 SLES 15 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. tboot 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 SLES 15. Confirm release, registration, and installed package:

cat /etc/os-release
SUSEConnect --status-text
SUSEConnect --list-extensions 2>/dev/null | head -30
rpm -q tboot
zypper info tboot | head -20

Exercise the workload that uses tboot 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 tail -200 /var/log/audit/audit.log
# For SUSE support, bundle evidence with supportconfig:
sudo supportconfig -R /var/tmp -B tboot

Root Cause Analysis

Root cause is documented in SUSE advisory SUSE-SU-2017:3090-1. SUSE security maintainers shipped fixes in the corresponding tboot update for SLES 15; 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 tboot
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 SLES 15 to capture the current state of tboot:

rpm -q tboot                              # installed NVR
rpm -V tboot                              # verify shipped files
sudo zypper patch-check                    # open patches
sudo zypper lp -r SUSE-SLE-Server-15-* 2>/dev/null | head
systemctl --failed --no-pager
sudo firewall-cmd --list-all
sudo aa-status                              # AppArmor profiles
rpm -ql tboot | grep -E '^/(usr/lib|etc)/systemd/(system|user)/[^/]+\.(service|socket|timer|path|target|mount)$'  # the units tboot REALLY ships - NO OUTPUT means it ships no service at all, so never run systemctl on it
rpm -ql tboot | grep -E '^/usr/sbin/rc[^/]+$'  # 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 tboot and the system bus.

   sudo journalctl -xe -f --no-pager

3. Inspect firewall posture (firewalld is the default on SLES 15+).

   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 tboot integrity and reinstall if anything is altered.

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

6. Correlate findings with /var/log/zypp/history, zypper history, and SUSE advisory SUSE-SU-2017:3090-1 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective zypper transaction referenced by SUSE advisory SUSE-SU-2017:3090-1, 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 tboot
# Unit name may differ from pkg name; check first:
rpm -q tboot                           # confirm new NVR

For kernel / glibc / systemd / openssl advisories a reboot is required (or SLE Live Patching where licensed):

sudo zypper ps -s                      # services using deleted libs
sudo systemctl reboot                  # or: sudo shutdown -r now
# SUSE Live Patching (kgraft / klp) avoids reboot for kernel CVEs:
sudo zypper install -y kernel-livepatch-$(uname -r | tr - _)
klp -v patches                         # active livepatches

Solution – Alternative Approaches

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

• Roll back via Snapper (Btrfs snapshots taken automatically before zypper transactions on SLES 15):

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

• Lock the package so zypper cannot upgrade it:

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

• Install an older NVR if a regression is suspected:

  zypper se -s tboot                     # show all available versions
  sudo zypper install --oldpackage tboot-<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

• Where SLE Live Patching is licensed, apply kernel fixes without reboot:

  klp -v patches                         # active livepatches
  sudo zypper install -y kernel-livepatch-$(uname -r | tr - _)

Verification & Acceptance Criteria

All of these should pass after the fix:

rpm -q tboot                                            # 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 tboot across two consecutive runs.

Rollback Plan

Capture state before any change:

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-tboot'   # explicit named snapshot
sudo snapper list | head

To revert if the patch is bad:

# Preferred on Btrfs root — boot the prior snapshot:
sudo snapper rollback <snapshot-id>
sudo systemctl reboot
# Or downgrade just the package:
sudo zypper install --oldpackage tboot-<older-NVR>
# Custom security policy cleanup:

Prevention & Hardening

Reduce the chance of this recurring on SLES 15:

• 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 sle-security-updates and watch suse.com/support/update.

• Mirror through SUSE Manager or RMT (Repository Mirroring Tool) for controlled rollouts:

  sudo zypper install -y rmt-server rmt-cli
  sudo rmt-cli sync
  sudo rmt-cli products enable SLES/15/x86_64

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

  sudo zypper al tboot

• Ensure Snapper is enabled on the root subvolume and pre/post hooks run for every zypper transaction:

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

• 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

• Subscribe to SUSE Live Patching so kernel CVEs can be remediated without reboot:

  sudo SUSEConnect -p sle-module-live-patching/15.0/x86_64
  sudo zypper install -y kernel-livepatch-$(uname -r | tr - _)
  klp -v patches

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

• Apply CIS SUSE Linux Enterprise Server Benchmark hardening.

Related Errors & Cross-Refs

Issues that commonly surface alongside a tboot 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

View all sles-15 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Primary reference: SUSE advisory SUSE-SU-2017:3090-1 (see also SUSE bugzilla). Manual pages useful on SLES 15:

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

Other resources: SUSE Linux Enterprise Server 15 documentation, suse.com/security, SUSE security blog, and per-package notes in /usr/share/doc/packages/tboot/ for components implicated in this advisory.