Ubuntu 16.04 — nova — multiple vulnerabilities (6 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: Ubuntu Security Notice USN-5866-1

Related CVEs: CVE-2015-9543 CVE-2017-18191 CVE-2020-17376 CVE-2021-3654 CVE-2022-37394 CVE-2019-14433

Upstream summary: It was discovered that Nova did not properly manage data logged into the
log file. An attacker with read access to the service's logs could exploit
this issue and may obtain sensitive information. This issue only affected
Ubuntu 16.04 ESM and Ubuntu 18.04 LTS. (CVE-2015-9543)

It was discovered that Nova did not properly handle attaching and
reattaching the encrypted volume. An attacker could possibly use this issue
to perform a denial of service attack. This issue only affec

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

On Ubuntu 16.04 hosts running nova, the vulnerable code is started by something else – a web or application server, or an on-demand supervisor such as inetd, xinetd or a systemd socket unit – rather than by a service of its own. Patching replaces the files on disk immediately, but a long-running parent that has already loaded them (PHP-FPM workers, an application server, a persistent worker pool) keeps serving the old code until it is recycled. Connection-per-process supervisors pick the fix up on the next connection, so the exposure window differs sharply between the two and is worth confirming rather than assuming. nova is started by a hosting server or an on-demand supervisor rather than by a unit of its own, so restart whatever launches it – not nova.

Environment & Reproduction

Reproduction targets Ubuntu 16.04 (xenial). Confirm release and installed package:

lsb_release -a
cat /etc/os-release
dpkg -l nova | tail -2
apt-cache policy nova
uname -r

Exercise the workload that uses nova while collecting:

needrestart -b -r l  # (pkg: needrestart) run as root; machine-readable. NEEDRESTART-SVC = units still mapping deleted libs, NEEDRESTART-SESS = login sessions, NEEDRESTART-KSTA = kernel state. -r l never restarts anything
needrestart -v -l -r l  # human-readable, libraries only (-l); names each PID and the obsolete file it still maps
checkrestart -v  # (pkg: debian-goodies) older alternative; add -p to report only deleted files owned by a dpkg package, -m for machine-readable
sudo journalctl -xe --no-pager | tail -200
sudo tail -200 /var/log/apt/history.log
sudo tail -200 /var/log/kern.log | grep -i apparmor

Root Cause Analysis

Root cause is documented in Ubuntu Security Notice USN-5866-1. Canonical security maintainers shipped fixes in the corresponding nova update for Ubuntu 16.04; running an outdated build leaves the host exposed to the failure modes described in the advisory. On this release the fix typically arrives via the Ubuntu Pro ESM (esm-infra / esm-apps) channels rather than the standard archive. Correlate apt history with the journal:

grep -A2 -B2 nova /var/log/apt/history.log
zgrep -A2 -B2 nova /var/log/apt/history.log.*.gz 2>/dev/null
cat /proc/sys/kernel/tainted   # non-zero = tainted kernel / out-of-tree modules

Quick Triage

Run these on Ubuntu 16.04 to capture the current state of nova:

dpkg -l nova | tail -1                  # installed version
dpkg -V nova                             # verify shipped files
sudo apt update && apt list --upgradable 2>/dev/null | grep -i security
systemctl daemon-reload  # only if the upgrade shipped changed unit files
systemctl daemon-reexec  # REQUIRED after a systemd / libsystemd upgrade: re-execs PID 1 against the new library without rebooting (needrestart flags this as 'systemd-manager')
needrestart -r i  # (pkg: needrestart) interactive: prompts per service. The safe default on a production box
needrestart -r a  # non-interactive: restarts EVERY flagged unit. Maintenance window only -- it will bounce databases and web servers without asking
sudo ufw status verbose 2>/dev/null | head -20
sudo aa-status 2>/dev/null | head -20
# If nova ships a service unit (unit/job name often differs from pkg name, e.g.
# bind9→named, apache2→apache2, postgresql-NN→postgresql@NN-main):
dpkg-query -L nova 2>/dev/null | grep -E '^/etc/init\.d/[^/]+$'  # legacy SysV init script; its basename is the service name for 'service <name> restart' on non-systemd hosts
systemctl list-unit-files --no-pager --type=service,socket,timer | grep -iF -- 'nova'  # fuzzy name match; -F is required because package names contain regex metacharacters ('+' in libstdc++6/g++-13 makes -E fail to match at all)

On xenial the standard archive no longer ships security fixes. Verify Ubuntu Pro ESM coverage:

# `pro` CLI not available on this release; check the older `ubuntu-advantage-tools`:
sudo ua status --format=json 2>/dev/null | head
apt-cache policy | grep -i esm

Step-by-Step Diagnosis

1. List failing services.

   systemctl --failed --no-pager

2. Tail the journal / syslog for nova.

   sudo journalctl -xe -f --no-pager

3. Inspect UFW (Uncomplicated Firewall) state.

   sudo ufw status numbered
   sudo ufw show added
   sudo iptables -L -n -v | head -30

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

   sudo journalctl -k 2>/dev/null | grep -i 'apparmor="DENIED"' | tail -30
   sudo aa-status
   # /etc/apparmor.d/usr.bin.nova or usr.sbin.nova — inspect first
   sudo aa-complain /etc/apparmor.d/usr.bin.nova 2>/dev/null || true

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

   sudo dpkg -V nova
   sudo debsums -c nova 2>/dev/null
   sudo apt install --reinstall -y nova

6. Correlate findings with /var/log/apt/history.log, /var/log/dpkg.log, and Ubuntu Security Notice USN-5866-1 to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective apt transaction referenced by Ubuntu Security Notice USN-5866-1, then reload the affected service:

sudo apt update
sudo apt -y install --only-upgrade nova
sudo systemctl daemon-reload
# Service name may differ from pkg name; check first:
dpkg -l nova | tail -1            # confirm new version

On xenial the standard archive is past EoL for security; enable Ubuntu Pro ESM to receive the fix:

# Older releases use the `ua` command:
sudo ua attach <token>
sudo ua enable esm-infra
sudo ua enable esm-apps
sudo apt update
sudo apt -y install --only-upgrade nova

For kernel / glibc / systemd / openssl advisories a reboot (or Livepatch) is required:

sudo apt install -y needrestart
sudo needrestart -r l       # list units that need restart
sudo systemctl reboot       # or: sudo shutdown -r now

Solution – Alternative Approaches

If the primary upgrade is not viable, pick from these:

• Hold the package so apt cannot upgrade it:

  sudo apt-mark hold nova
  apt-mark showhold | grep nova
  # Release the hold later with:
  sudo apt-mark unhold nova

• Pin a known-good version via apt preferences:

  # /etc/apt/preferences.d/nova.pref
  Package: nova
  Pin: version <good-version>
  Pin-Priority: 1001

• Downgrade to an older version if a regression is suspected:

  apt-cache madison nova
  sudo apt install --allow-downgrades -y nova=<older-version>

• Investigate AppArmor blocking the new binary; switch to complain briefly, capture denials, then re-enforce:

  sudo aa-complain /etc/apparmor.d/usr.bin.nova 2>/dev/null
  # reproduce the failure
  sudo journalctl -k | grep apparmor | tail
  sudo aa-enforce /etc/apparmor.d/usr.bin.nova 2>/dev/null

• Take only the security pocket update and defer the full point-release upgrade:

  sudo apt -y install --only-upgrade -t xenial-security nova

Verification & Acceptance Criteria

All of these should pass after the fix is applied:

dpkg -l nova | tail -1                                  # expected fixed version
apt list --upgradable 2>/dev/null | grep -i security || echo OK
sudo ufw status numbered | head
sudo aa-status 2>/dev/null | head -5

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

Rollback Plan

Capture state before any change:

apt list --installed 2>/dev/null > /root/apt-pre.txt
dpkg --get-selections > /root/dpkg-pre.txt
# ZFS-on-root (Ubuntu 20.04+ default installer option):
sudo zfs snapshot rpool/ROOT/ubuntu@pre-nova
# LVM-on-root:
sudo lvcreate -L 4G -s -n root_pre_patch /dev/<vg>/<root-lv>

To revert:

sudo apt install --allow-downgrades -y nova=<old-version>
sudo systemctl daemon-reload
# Kernel rollback: pick the prior kernel from the GRUB menu, then:
sudo systemctl reboot
# ZFS rollback (rolls the whole root dataset):
sudo zfs rollback -r rpool/ROOT/ubuntu@pre-nova

Prevention & Hardening

Reduce the chance of this recurring on Ubuntu 16.04 (xenial):

• Enable scheduled security updates via unattended-upgrades:

  sudo apt install -y unattended-upgrades update-notifier-common
  sudo dpkg-reconfigure -plow unattended-upgrades
  # /etc/apt/apt.conf.d/50unattended-upgrades:
  Unattended-Upgrade::Allowed-Origins { "${distro_id}:${distro_codename}-security"; };

• Install needrestart so services restart automatically after library upgrades:

  sudo apt install -y needrestart
  # /etc/needrestart/needrestart.conf -> $nrconf{restart} = 'a';

• Attach Ubuntu Pro for ESM (mandatory on this past-EoL release) and Livepatch where supported:

  sudo ua attach <token>
  sudo ua enable esm-infra
  sudo ua enable esm-apps

• Subscribe to ubuntu-security-announce and watch ubuntu.com/security/cves.

• Monitor file integrity with debsums and AIDE:

  sudo apt install -y debsums aide
  sudo debsums -ca
  sudo aideinit && sudo mv /var/lib/aide/aide.db.new /var/lib/aide/aide.db
  sudo aide --check

• For estate-wide patching, manage with Canonical Landscape:

  sudo apt install -y landscape-client
  sudo landscape-config

• Keep AppArmor profiles in enforce mode and apply CIS Ubuntu Linux Benchmark hardening.

Related Errors & Cross-Refs

Issues that commonly surface alongside a nova update: apt lock contention, broken dpkg state, systemd ordering cycles, AppArmor denials, and UFW rule drift. Useful triage:

sudo dpkg --configure -a
sudo apt --fix-broken install
systemd-analyze critical-chain
sudo journalctl -k 2>/dev/null | grep -i apparmor | tail
cat /proc/sys/kernel/tainted

View all ubuntu-16-04 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Primary reference: Ubuntu Security Notice USN-5866-1. Manual pages useful on Ubuntu 16.04:

man apt
man apt-get
man apt-mark
man dpkg
man systemctl
man journalctl
man ufw
man apparmor
man aa-status
man unattended-upgrades
man ua

Other resources: Ubuntu Security Notices, Ubuntu CVE Tracker, Ubuntu upgrade notes, and per-package notes in /usr/share/doc/nova/ for components implicated in this advisory.