Shell Command Injection with the hostname

I can't imagine the effort involved in hardening all applications to treat the hostname as untrusted input.

ISPs that sell vservers are really no different from Intel or AMD or whoever makes your CPU -- you trust them completely and totally with your data, your executables, and your entire operating environment. They can inject anything they wish into your system's memory whenever they wish.

Making sure the dhcp clients don't allow setting these kinds of hostnames however, that might be a good idea. Enforcing the usual dns guidelines of a-zA-Z0-9-_ might be worthwhile..

Thanks

I agree,
i think the hostname should be in the hands of the kernel only.
Should not be overwritten by /etc/hostname.sh.

typo ... the path is
/etc/init.d/hostname.sh

german demo video
https://www.youtube.com/watch?v=qYuVzHsklS8

Patch :

HOSTNAME=${HOSTNAME//[^A-Za-z0-9-_]/_}

Thats better ... (the "-" was wrong in my previous posting )

HOSTNAME="${HOSTNAME//[^A-Za-z0-9_\-]/x}"

i attached a modified hostname.sh wich uses bash.

it can be startet manualy with

sudo /etc/init.d/hostname.sh start

The command should somehow run at startup ... but does not by default ?

Workaround ...
to make my modified "hostname.sh" script run at startup, i changed the file /etc/rc.local

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

/etc/init.d/hostname.sh start

exit 0

#! /bin/sh
# run this as root early in the boot order. No other script like hostname.sh should run later
HOSTNAME="$(hostname|sed 's/[^A-Za-z0-9_\-\.]/x/g')";hostname "$HOSTNAME"

script

I'm not sure what the attack vector here is. /etc/hostname is only writeable by root.

Is there any way for an attacker to control /etc/hostname?

@Marc
Yes , if some application has a bug , for example MintNanny :
https://bugs.launchpad.net/linuxmint/+bug/1460835

This issue was assigned CVE-2016-0634. See the oss-security notice here:

  http://openwall.com/lists/oss-security/2016/09/16/8

This bug was fixed in the package bash - 4.3-15ubuntu1.1

---------------
bash (4.3-15ubuntu1.1) yakkety-security; urgency=medium

  * SECURITY UPDATE: word expansions on the prompt strings (LP: #1507025)
    - debian/patches/bash43-047.diff: add quoting to parse.y, y.tab.c.
    - CVE-2016-0634
  * SECURITY UPDATE: code execution via crafted SHELLOPTS and PS4
    (LP: #1689304)
    - debian/patches/bash43-048.diff: check for root in variables.c.
    - CVE-2016-7543
  * SECURITY UPDATE: restricted shell bypass via use-after-free
    - debian/patches/bash44-006.diff: check for negative offsets in
      builtins/pushd.def.
    - CVE-2016-9401

 -- Marc Deslauriers <email address hidden> Tue, 16 May 2017 07:44:56 -0400

This bug was fixed in the package bash - 4.3-7ubuntu1.7

---------------
bash (4.3-7ubuntu1.7) trusty-security; urgency=medium

  * SECURITY UPDATE: word expansions on the prompt strings (LP: #1507025)
    - debian/patches/bash43-047.diff: add quoting to parse.y, y.tab.c.
    - CVE-2016-0634
  * SECURITY UPDATE: code execution via crafted SHELLOPTS and PS4
    (LP: #1689304)
    - debian/patches/bash43-048.diff: check for root in variables.c.
    - CVE-2016-7543
  * SECURITY UPDATE: restricted shell bypass via use-after-free
    - debian/patches/bash44-006.diff: check for negative offsets in
      builtins/pushd.def.
    - CVE-2016-9401

 -- Marc Deslauriers <email address hidden> Tue, 16 May 2017 07:52:48 -0400

This bug was fixed in the package bash - 4.3-14ubuntu1.2

---------------
bash (4.3-14ubuntu1.2) xenial-security; urgency=medium

  * SECURITY UPDATE: word expansions on the prompt strings (LP: #1507025)
    - debian/patches/bash43-047.diff: add quoting to parse.y, y.tab.c.
    - CVE-2016-0634
  * SECURITY UPDATE: code execution via crafted SHELLOPTS and PS4
    (LP: #1689304)
    - debian/patches/bash43-048.diff: check for root in variables.c.
    - CVE-2016-7543
  * SECURITY UPDATE: restricted shell bypass via use-after-free
    - debian/patches/bash44-006.diff: check for negative offsets in
      builtins/pushd.def.
    - CVE-2016-9401

 -- Marc Deslauriers <email address hidden> Tue, 16 May 2017 07:51:45 -0400

Even our oldest supported (as extended security maintenance) release Ubuntu 12.04 had bash 4.2 (https://launchpad.net/ubuntu/+source/bash) - so whether this affects bash 3.2.57 is not relevant to Ubuntu anymore.