Why does sudo change the PATH?

Question

This is an annoying function a feature of sudo on many distributions.

To work around this "problem" on ubuntu I do the following in my ~/.bashrc

alias sudo='sudo env PATH=$PATH'

Note the above will work for commands that don't reset the $PATH themselves. However `su' resets it's $PATH so you must use -p to tell it not to. I.E.:

sudo su -p

In case someone else runs accross this and wants to just disable all path variable changing for all users.
Access your sudoers file by using the command:visudo. You should see the following line somewhere:

Defaults env_reset

which you should add the following on the next line

Defaults !secure_path

secure_path is enabled by default. This option specifies what to make $PATH when sudoing. The exclamation mark disables the feature.

PATH is an environment variable, and as such is by default reset by sudo.

You need special permissions to be permitted to do this.

From man sudo

       -E  The -E (preserve environment) option will override the env_reset
           option in sudoers(5)).  It is only available when either the match-
           ing command has the SETENV tag or the setenv option is set in sudo-
           ers(5).

       Environment variables to be set for the command may also be passed on
       the command line in the form of VAR=value, e.g.
       LD_LIBRARY_PATH=/usr/local/pkg/lib.  Variables passed on the command
       line are subject to the same restrictions as normal environment vari-
       ables with one important exception.  If the setenv option is set in
       sudoers, the command to be run has the SETENV tag set or the command
       matched is ALL, the user may set variables that would overwise be for-
       bidden.  See sudoers(5) for more information.

An Example of usage:

cat >> test.sh
env | grep "MYEXAMPLE" ;
^D

sh test.sh 
MYEXAMPLE=1 sh test.sh
# MYEXAMPLE=1
MYEXAMPLE=1 sudo sh test.sh 
MYEXAMPLE=1 sudo MYEXAMPLE=2 sh test.sh 
# MYEXAMPLE=2

update

man 5 sudoers : 

     env_reset       If set, sudo will reset the environment to only contain
                       the LOGNAME, SHELL, USER, USERNAME and the SUDO_* vari-
                       ables.  Any variables in the caller's environment that
                       match the env_keep and env_check lists are then added.
                       The default contents of the env_keep and env_check
                       lists are displayed when sudo is run by root with the
                       -V option.  If sudo was compiled with the SECURE_PATH
                       option, its value will be used for the PATH environment
                       variable.  This flag is on by default.

So may need to check that this is/is not compiled in.

It is by default in Gentoo

# ( From the build Script )
....
ROOTPATH=$(cleanpath /bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/opt/bin${ROOTPATH:+:${ROOTPATH}})
....
econf --with-secure-path="${ROOTPATH}" 

Looks like this bug has been around for quite a while! Here are some bug references you may find helpful (and may want to subscribe to / vote up, hint, hint...):

---

Debian bug #85123 ("sudo: SECURE_PATH still can't be overridden") (from 2001!)

It seems that Bug#20996 is still present in this version of sudo. The changelog says that it can be overridden at runtime but I haven't yet discovered how.

They mention putting something like this in your sudoers file:

Defaults secure_path="/bin:/usr/bin:/usr/local/bin"

but when I do that in Ubuntu 8.10 at least, it gives me this error:

visudo: unknown defaults entry `secure_path' referenced near line 10

---

Ubuntu bug #50797 ("sudo built with --with-secure-path is problematic")

Worse still, as far as I can tell, it is impossible to respecify secure_path in the sudoers file. So if, for example, you want to offer your users easy access to something under /opt, you must recompile sudo.

---

Yes. There needs to be a way to override this "feature" without having to recompile. Nothing worse then security bigots telling you what's best for your environment and then not giving you a way to turn it off.

---

This is really annoying. It might be wise to keep current behavior by default for security reasons, but there should be a way of overriding it other than recompiling from source code! Many people ARE in need of PATH inheritance. I wonder why no maintainers look into it, which seems easy to come up with an acceptable solution.

---

I worked around it like this:

mv /usr/bin/sudo /usr/bin/sudo.orig

then create a file /usr/bin/sudo containing the following:

#!/bin/bash
/usr/bin/sudo.orig env PATH=$PATH "$@"

then your regular sudo works just like the non secure-path sudo

---

Ubuntu bug #192651 ("sudo path is always reset")

Given that a duplicate of this bug was originally filed in July 2006, I'm not clear how long an ineffectual env_keep has been in operation. Whatever the merits of forcing users to employ tricks such as that listed above, surely the man pages for sudo and sudoers should reflect the fact that options to modify the PATH are effectively redundant.

Modifying documentation to reflect actual execution is non destabilising and very helpful.

---

Ubuntu bug #226595 ("impossible to retain/specify PATH")

I need to be able to run sudo with additional non-std binary folders in the PATH. Having already added my requirements to /etc/environment I was surprised when I got errors about missing commands when running them under sudo.....

I tried the following to fix this without sucess:

1. Using the "sudo -E" option - did not work. My existing PATH was still reset by sudo

2. Changing "Defaults env_reset" to "Defaults !env_reset" in /etc/sudoers -- also did not work (even when combined with sudo -E)

3. Uncommenting env_reset (e.g. "#Defaults env_reset") in /etc/sudoers -- also did not work.

4. Adding 'Defaults env_keep += "PATH"' to /etc/sudoers -- also did not work.

Clearly - despite the man documentation - sudo is completely hardcoded regarding PATH and does not allow any flexibility regarding retaining the users PATH. Very annoying as I can't run non-default software under root permissions using sudo.

This seemed to work for me

sudo -i 

which takes on the non-sudo PATH

I think it is in fact desirable to have sudo reset the PATH: otherwise an attacker having compromised your user account could put backdoored versions of all kinds of tools on your users' PATH, and they would be executed when using sudo.

(of course having sudo reset the PATH is not a complete solution to these kinds of problems, but it helps)

This is indeed what happens when you use

Defaults env_reset

in /etc/sudoers without using exempt_group or env_keep.

This is also convenient because you can add directories that are only useful for root (such as /sbin and /usr/sbin) to the sudo path without adding them to your users' paths. To specify the path to be used by sudo:

Defaults secure_path="/bin:/usr/bin:/usr/local/bin:/sbin:/usr/sbin"

Works now using sudo from the karmic repositories. Details from my configuration:

root@sphinx:~# cat /etc/sudoers | grep -v -e '^$' -e '^#'
Defaults    env_reset
Defaults    secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/grub-1.96/sbin:/opt/grub-1.96/bin"
root    ALL=(ALL) ALL
%admin ALL=(ALL) ALL
root@sphinx:~# cat /etc/apt/sources.list
deb http://au.archive.ubuntu.com/ubuntu/ jaunty main restricted universe
deb-src http://au.archive.ubuntu.com/ubuntu/ jaunty main restricted universe

deb http://au.archive.ubuntu.com/ubuntu/ jaunty-updates main restricted universe
deb-src http://au.archive.ubuntu.com/ubuntu/ jaunty-updates main restricted universe

deb http://security.ubuntu.com/ubuntu jaunty-security main restricted universe
deb-src http://security.ubuntu.com/ubuntu jaunty-security main restricted universe

deb http://au.archive.ubuntu.com/ubuntu/ karmic main restricted universe
deb-src http://au.archive.ubuntu.com/ubuntu/ karmic main restricted universe

deb http://au.archive.ubuntu.com/ubuntu/ karmic-updates main restricted universe
deb-src http://au.archive.ubuntu.com/ubuntu/ karmic-updates main restricted universe

deb http://security.ubuntu.com/ubuntu karmic-security main restricted universe
deb-src http://security.ubuntu.com/ubuntu karmic-security main restricted universe
root@sphinx:~# 

root@sphinx:~# cat /etc/apt/preferences 
Package: sudo
Pin: release a=karmic-security
Pin-Priority: 990

Package: sudo
Pin: release a=karmic-updates
Pin-Priority: 960

Package: sudo
Pin: release a=karmic
Pin-Priority: 930

Package: *
Pin: release a=jaunty-security
Pin-Priority: 900

Package: *
Pin: release a=jaunty-updates
Pin-Priority: 700

Package: *
Pin: release a=jaunty
Pin-Priority: 500

Package: *
Pin: release a=karmic-security
Pin-Priority: 450

Package: *
Pin: release a=karmic-updates
Pin-Priority: 250

Package: *
Pin: release a=karmic
Pin-Priority: 50
root@sphinx:~# apt-cache policy sudo
sudo:
  Installed: 1.7.0-1ubuntu2
  Candidate: 1.7.0-1ubuntu2
  Package pin: 1.7.0-1ubuntu2
  Version table:
 *** 1.7.0-1ubuntu2 930
         50 http://au.archive.ubuntu.com karmic/main Packages
        100 /var/lib/dpkg/status
     1.6.9p17-1ubuntu3 930
        500 http://au.archive.ubuntu.com jaunty/main Packages
root@sphinx:~# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/opt/grub-1.96/sbin:/opt/grub-1.96/bin
root@sphinx:~# exit
exit
abolte@sphinx:~$ echo $PATH
/home/abolte/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/opt/grub-1.96/sbin:/opt/grub-1.96/bin:/opt/chromium-17593:/opt/grub-1.96/sbin:/opt/grub-1.96/bin:/opt/xpra-0.0.6/bin
abolte@sphinx:~$ 

It's wonderful to finally have this solved without using a hack.