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[Dan Streetman <ddstreet@xxxxxxxxxxxxx>]

** Changed in: sudo (Ubuntu Disco)
       Status: In Progress => Won't Fix

** Changed in: sudo (Ubuntu Cosmic)
       Status: In Progress => Won't Fix

** Changed in: sudo (Ubuntu Bionic)
     Assignee: Dan Streetman (ddstreet) => (unassigned)

** Changed in: sudo (Ubuntu Xenial)
     Assignee: Dan Streetman (ddstreet) => (unassigned)

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https://bugs.launchpad.net/bugs/1556302

Title:
  Ubuntu patch to add HOME to env_keep makes custom commands vulnerable
  by default

Status in Release Notes for Ubuntu:
  New
Status in sudo package in Ubuntu:
  Fix Released
Status in sudo source package in Xenial:
  In Progress
Status in sudo source package in Bionic:
  In Progress
Status in sudo source package in Cosmic:
  Won't Fix
Status in sudo source package in Disco:
  Won't Fix
Status in sudo source package in Eoan:
  Fix Released

Bug description:
  [impact]

  sudo does not set HOME to the target user's HOME

  [test case]

  ddstreet@thorin:~$ sudo printenv | grep HOME
  HOME=/home/ddstreet

  [regression potential]

  this is a significant behavior change.  As mentioned in comment 11
  (and later, and other bugs duped to this, and the mailing list
  discussion, etc) users of Ubuntu so far have been used to running sudo
  with their own HOME set, not root's HOME.  Therefore, it's
  inappropriate to change this behavior for existing releases; this
  should be changed starting in Eoan, and only the sudo and sudoers man
  pages changed in previous releases to indicate the actual behavior of
  sudo in those releases.

  [other info]

  Shortly after upstream changed the behavior, the patch to keep HOME as
  the calling (instead of target) user was added in bug 760140.

  For quick reference to anyone coming to this bug, the pre-19.10
  behavior (of sudo keeping the calling user's $HOME) can be disabled by
  running 'sudo visudo' and adding this line:

  Defaults        always_set_home

  or, run sudo with the -H param.

  --
  original description:
  --

  I wanted to allow certain users to execute a python script as another user, so I created the following sudoers config:
  Defaults env_reset
  source_user ALL=(target_user) NOPASSWD: /home/target_user/bin/script.py

  This results in a highly insecure Python environment because the
  source user can set HOME and override any Python package by putting
  files in $HOME/.local/lib/python*/site-packages/.

  This should be a safe configuration because the default behaviour (as
  specified in the man page) is that env_reset will replace HOME with
  the target user's home directory. The "env_reset" option even has
  special behaviour for bash which has its own potential environment
  vulnerabilities.

  However there is an Ubuntu-specific patch in the package
  (keep_home_by_default.patch) that makes sudo preserve HOME by default,
  which negates the correct behaviour of "env_reset". It should not be
  necessary to explicitly specify the "always_set_home" option in order
  to negate this patch.

  The patch should be removed and the default /etc/sudoers should
  explicitly add HOME to "env_keep" for the "allow admins to run any
  command as root" entries, to get the desired behaviour without
  creating security issues for other sudoers commands.

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