yahoo-eng-team team mailing list archive

[Brian Murray <1918303@xxxxxxxxxxxxxxxxxx>]

cloud-init (21.1-19-gbad84ad4-0ubuntu1) hirsute; urgency=medium

  * d/cloud-init.postinst: Change output log permissions on upgrade
    (LP: #1918303)

** Also affects: cloud-init (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: cloud-init (Ubuntu)
       Status: New => Fix Released

-- 
You received this bug notification because you are a member of Yahoo!
Engineering Team, which is subscribed to cloud-init.
https://bugs.launchpad.net/bugs/1918303

Title:
  Randomly set credentials written in cleartext to world-readable file

Status in cloud-init:
  Fix Committed
Status in cloud-init package in Ubuntu:
  Fix Released

Bug description:
  ## Summary

  cloud-init allows administrators to set passwords for user accounts
  via the chpasswd configuration module. Administrators can instruct
  cloud-init to set a random password generated at runtime using the 'R'
  or 'RANDOM' keywords.

  However, cloud-init appears to write all randomly generated passwords
  in cleartext to stderr. Cloud-init's default logging configuration, in
  file /etc/cloud/cloud.cfg.d/05_logging.cfg, redirects both stdout and
  stderr to the log file /var/log/cloud-init-output.log. The file
  /var/log/cloud-init-output.log is world readable. Thus, any
  unprivileged account on the system can view the cleartext password for
  any account which had a random password generated at runtime. The
  credentials are not redacted in the log.

  ## Reproduction

  Pre-requisites: A device with Ubuntu Server 20.04 installed. Ubuntu
  Server comes with cloud-init pre-installed out of the box, but the
  latest release of cloud-init as of this report (21.1) is not available
  in 20.04's apt repositories. You may need to install v21.1 manually.
  You will also need an exsiting admin account with root privileges.

  1. Login as admin.
  2. Create an unprivileged user account, bob, and set a password. We will use this account to demonstrate unprivileged account access to generated passwords.
  sudo adduser bob
  3. Create another unprivileged user account, alice, and set a password. We will change this account's password with cloud-init.
  sudo adduser alice
  4. Create and open configuration file /etc/cloud/cloud.cfg.d/95_chpasswd.cfg using vim or other editor of your choice.
  sudo vim /etc/cloud/cloud.cfg.d/95_chpasswd.cfg
  5. Add the following chpasswd configuration content to the file then save and exit.
  chpasswd:
    list: |
      alice:RANDOM
  6. cloud-init only runs the chpasswd function on first boot of the OS that cloud-init knows about. For proof of concept purposes, we need to simulate a new instance. Run:
  sudo cloud-init clean
  to reset cloud-init's state.
  7. Reboot the system.
  sudo reboot
  8. Login as unprivileged user bob.
  9. View the password by runnnig
  cat /var/log/cloud-init-output.log | grep alice
  10. Alice's temporary password should appear on terminal in the form alice:<password>
  11. Logout and log back in to the system as alice using the temporary password. You should get access and prompted to set a new password, which confirms the password bob retrieved from the logs is the actual password for alice's account.

  ## Impact

  Any unprivileged user on the system can retrieve all cloud-init
  randomly set credentials. These could potentially be used to access
  other accounts.

  # Notes

  If 'expire: false' is added to the chpasswd config, then leaked
  passwords remain valid until manually changed and increases the risk
  of unauthorized account access. Otherwise, the default behaviour
  prompts accounts to set a new password at next login, reducing the
  time window for unauthorized access.

  Accounts not used for interactive login might not get passwords
  changed or accounts might get a password set but then not authenticate
  for some time. The precise impact and duration of valid exposed
  credentials appears dependent somewhat on each cloud-init customer's
  environment and how they use cloud-init to set credentials.

  I'm not sure the best approach to patch this but perhaps the
  credentials could be written to cloud-init's protected directories or
  files which restrict access to root users only, such as /var/run
  /cloud-init/instance-data-sensitive.json?

  Line 214 of https://github.com/canonical/cloud-
  init/blob/master/cloudinit/config/cc_set_passwords.py checks if any
  random passwords were set and if so prints each one to stderror. This
  might be the root cause.

  Tested on Ubuntu Server 20.04.02, cloud-init latest release 21.1 as of report time. If I can provide any further information please let me know. Thanks!
  -Carl

To manage notifications about this bug go to:
https://bugs.launchpad.net/cloud-init/+bug/1918303/+subscriptions