Debian 10 — qemu — multiple vulnerabilities (6 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: Debian Security Tracker

Related CVEs: CVE-2019-12068 CVE-2019-13164 CVE-2019-15890 CVE-2020-10756 CVE-2020-12829 CVE-2020-8608

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

Nothing visibly changes on a Debian 10 host until qemu is next invoked: it runs, exits and leaves no daemon behind, so there is no restart loop or service log to watch. Exposure is per-invocation, and the invocations that matter are the unattended ones — cron jobs, backup and deployment scripts, CI runners, and anything passing attacker-influenced input such as a remote URL, a supplied archive or an untrusted filename. Where qemu is run under sudo or from a privileged job, the same flaw becomes local privilege escalation. qemu ships command-line programs that run when invoked and then exit, so there is no unit to restart — systemctl and journalctl -u have nothing to act on; only the next invocation matters.

Environment & Reproduction

Reproduction targets Debian 10 (buster). Confirm release and installed package:

cat /etc/debian_version
lsb_release -a 2>/dev/null || cat /etc/os-release
dpkg -l qemu | tail -2
apt-cache policy qemu
dpkg-query -W -f='${Status}\n' qemu

Exercise the workload that uses qemu while collecting:

sudo journalctl -xe --no-pager | tail -200
sudo tail -200 /var/log/apt/history.log
sudo tail -200 /var/log/dpkg.log

Root Cause Analysis

Root cause is tracked at Debian Security Tracker. The Debian Security Team shipped fixes in the corresponding qemu point release for Debian 10 (suite buster-security); running an outdated build leaves the host exposed to the failure modes referenced above. Correlate apt history with the journal:

grep -A2 -B2 qemu /var/log/apt/history.log
zgrep -A2 -B2 qemu /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 Debian 10 to capture the current state of qemu:

dpkg -l qemu | tail -1                   # installed version
dpkg -V qemu                              # verify shipped files
sudo apt update && apt list --upgradable 2>/dev/null | grep -i security
systemctl --failed --no-pager
sudo iptables -L -n -v 2>/dev/null | head -30
sudo aa-status 2>/dev/null | head -20      # AppArmor profiles
dpkg-query -L qemu 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 -- 'qemu'  # fuzzy name match; -F is required because package names contain regex metacharacters ('+' in libstdc++6/g++-13 makes -E fail to match at all)

Step-by-Step Diagnosis

1. List failed systemd units.

   systemctl --failed --no-pager

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

   sudo journalctl -xe -f --no-pager

3. Inspect firewall state (this OS defaults to iptables-legacy).

   sudo iptables -L -n -v
   sudo iptables-save | head

4. Verify qemu file integrity and reinstall if anything is altered.

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

5. Check AppArmor denials (Debian 11+ default-enabled).

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

6. Correlate findings with /var/log/apt/history.log, /var/log/dpkg.log, and Debian Security Tracker to pin the change that introduced the regression.

Solution – Primary Fix

Apply the corrective apt transaction documented in Debian Security Tracker from the security suite, then reload the affected unit:

sudo apt update
sudo apt -y install --only-upgrade qemu
# Unit name may differ from package name; check first:
dpkg -l qemu | tail -1                # confirm new version

For Debian 9/10 (LTS): the fixed package may live in the Freexian LTS suite. Ensure your sources list includes:

# /etc/apt/sources.list.d/buster-lts.list
deb http://deb.freexian.com/extended-lts buster-lts main contrib non-free

For kernel / glibc / systemd / openssl advisories a reboot is required:

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

Solution – Alternative Approaches

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

• Pin a known-good version via apt preferences:

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

• Mark the package on hold so apt cannot upgrade it:

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

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

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

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

  # /etc/apt/sources.list.d/buster-security-only.list
  deb http://security.debian.org/debian-security buster-security main contrib non-free
  # then:
  sudo apt update && sudo apt -y install --only-upgrade -t buster-security qemu

• Investigate AppArmor blocking the new binary; switch the profile to complain mode briefly:

  # reproduce, capture denials, then re-enforce:

Verification & Acceptance Criteria

All of these should pass after the fix is applied:

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

The conditions described in the advisory must no longer be reported for qemu 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
# LVM snapshot of the root LV (only if root sits on LVM):
sudo lvcreate -L 4G -s -n root_pre_patch /dev/<vg>/<root-lv>

To revert:

sudo apt install --allow-downgrades -y qemu=<old-version>
# If a kernel was rolled back, reboot and select the previous kernel from GRUB:
sudo systemctl reboot
# LVM snapshot merge (offline / on next reboot):
sudo lvconvert --merge /dev/<vg>/root_pre_patch

Prevention & Hardening

Reduce the chance of this recurring on Debian 10:

• Enable scheduled security updates via unattended-upgrades:

  sudo apt install -y unattended-upgrades apt-listchanges
  sudo dpkg-reconfigure -plow unattended-upgrades
  # /etc/apt/apt.conf.d/50unattended-upgrades:
  Unattended-Upgrade::Origins-Pattern { "origin=Debian,codename=${distro_codename},label=Debian-Security"; };

• Install needrestart so services restart automatically after library upgrades:

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

• Subscribe to debian-security-announce and watch security-tracker.debian.org.

• Mirror locally for controlled rollouts:

  sudo apt install -y apt-mirror
  # /etc/apt/mirror.list:
  deb http://deb.debian.org/debian buster main contrib non-free
  deb http://security.debian.org/debian-security buster-security main contrib non-free
  sudo apt-mirror

• Monitor file integrity with debsums and AIDE:

  sudo apt install -y debsums aide
  sudo debsums -ca           # report only changed conffile-less files
  sudo aideinit && sudo mv /var/lib/aide/aide.db.new /var/lib/aide/aide.db
  sudo aide --check

• Apply CIS Debian Linux Benchmark hardening and review auditd rules in /etc/audit/rules.d/.

• For Debian 9/10 LTS, subscribe to Freexian Extended LTS so that buster keeps getting security fixes past Debian end-of-life.

Related Errors & Cross-Refs

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

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

View all debian-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Primary reference: Debian Security Tracker. Manual pages useful on Debian 10:

man apt
man apt-get
man apt-mark
man dpkg
man systemctl
man journalctl
man iptables
man apparmor
man unattended-upgrades

Other resources: The Debian Administrator’s Handbook, Debian Security FAQ, Debian Security Tracker, and per-package notes in /usr/share/doc/qemu/ for components implicated in this advisory.