Linux web browser station (formerly "The Linux Public Web Browser mini-HOWTO")
Anton Chuvakin, v0.0.5 10 October 2000
Describes the setup of Internet kiosk-type system based on Linux to be deployed to provide public Internet/webmail access.
- 1.1 Disclaimer
- 1.2 Credits
- 1.3 New versions of this document
- 1.4 Changes Fri Sep 22 14:32:32 EDT 2000
- 1.5 TODO
- 1.6 Feedback
- 1.7 Copyright information
- 2.1 Copyright and Disclaimer
- 2.2 Introduction
- 2.3 Before you begin
- 2.4 Add the guest account
2.5 Create or edit the following files in
2.6 Make a
- 2.7 Try it
- 2.8 Changing preferences
- 3.1 Install RH
- 3.2 Clean-up packages
- 3.3 Install ssh
- 3.4 Make a boot floppy
- 3.5 Modify configs
- 3.6 Create user
- 3.7 Change Netscape settings
- 3.8 Chown the home directory
- 3.9 Config lilo
- 3.10 REMOVE binaries
- 3.11 Physical security
- 3.12 Some final touches
The directions below will produce the RedHat (currently version 6.2 is used, 7.0 is in development) Linux system that boots into the bare (=no window manager, like gnome, kde or fvwm2) X server and starts Netscape Navigator (not Communicator, which includes Main and News clients). Upon exiting the browser the X server is restarted and the new Netscape process is launched as needed. The system is intended for Internet Kiosks and similar applications. Security is emphasized at all the stages of the setup.
This HOWTO will be updated (maybe significantly) as long as more reports about the deployment of such boxes will arrive.
Use the information in this document at your own risk. I disavow any potential liability for the contents of this document. Use of the concepts, examples, and/or other content of this document is entirely at your own risk.
All copyrights are owned by their owners, unless specifically noted otherwise. Use of a term in this document should not be regarded as affecting the validity of any trademark or service mark.
Naming of particular products or brands should not be seen as endorsements.
You are strongly recommended to take a backup of your system before major installation and backups at regular intervals.
In this version I have the pleasure of acknowledging the previous maintainer of this HOWTO who nicely agreed to transfer it to me
New versions of this document can be found at
from 0.0.4 to 0.0.3
- Merged with old HOWTO
from 0.0.2 to 0.0.3
- references added
- abstract finished
- Write abstract
- Suggested hardware
.Xdefaultsdisable some keys (Alt-Ctrl-F1)
- X server port 6000 attacks, do something about them
- X server under root, bad
- Eliminate more unneeded RPMs
- Implement /etc/pam.d/limits.conf to prevent netscape bloat and system crash (well, by causing it to crash before bloat ;-) ), see Security HOWTO
- Protect some files with chattr is nice
- Provided CDROM booting considerations
- Redo everything for RedHat 7.0
All comments, error reports, additional information (very much
appreciated!!!) and criticism of all sorts should be directed to:
My PGP key is located at
This document is copyrighted (c) 2000 Anton Chuvakin, and parts of it are Copyright 1997 Donald B. Marti Jr. where marked as such
2. OLD GUIDE: The Linux Public Web
Browser mini-HOWTO by Donald B. Marti
v0.3, 5 January 1998
The basic idea here is to give web access to people who wander by, while limiting their ability to mess anything up.
Copyright 1997 Donald B. Marti Jr. This document may be redistributed under the terms of the Linux Documentation Project license.
This document currently contains information for Netscape Navigator only, but I plan to add notes for other browsers too as I get the necessary information. If you try this with a different browser, please let me know.
The basic idea here is to give web access to people who wander by, while limiting their ability to mess anything up.
This setup was originally intended for trade shows, but it might be applicable other places you want to have a web browser going without having to babysit a computer.
Following these instructions does not make your system bulletproof or idiot-proof.
You need a graphical browser
This document assumes that you already have a running graphical web browser, such as Netscape Navigator, on your system. You should have permission to use your graphical web browser. If you want to use Netscape Navigator in a commercial setting, you can buy a copy with appropriate license through Caldera.
You need to be able to add an account
If you don't have the right to be root, get the system
administrator to add the ``
guest'' account and give
you ownership of
guest's home directory. Skip to the
``Create or edit the following files'' step ( Create or edit the following files in
/home/guest) when he or she is done.
httpd for a stand-alone web browsing station
If you are setting up a web browsing station to run stand-alone,
without a network connection, you should have
working and the web documents installed. To tell if this is the
You should get the text of the home page on your system.
lynx -dump http://localhost/
As root, run
adduser to add a user named
guest. Then enter
to set the password for the
guestaccount. This should be something easy to remember, like ``
guest''. You will be telling people this password. Don't make it the same as your own password.
guest's home directory owned by you. Enter
chown me.mygroup /home/guest
me'' with your regular username and ``
mygroup'' with your group name. (On Red Hat Linux, these will be the same, since every user has his or her own group.)
You should now exit and do the rest of the steps as yourself, not root.
This means that when
guestlogs in, the login shell will start up the X Window System right away.
This means that when X starts,
guestjust gets the web browser, no window manager. If you prefer another web browser, do something else.
.Xclients should be executable by
to make it so.
chmod 755 /home/guest/.Xclients
If you use
xdm(1) to log people in, this file should make guest get the web browser as if he or she had logged in normally. The file
.xsessionshould be executable by
to make it so.
chmod 755 /home/guest/.xsession
This file disables blink tags, drag-to-select, and some of the keyboard commands. It also makes all mouse buttons do the same thing, hides the menu bar, and makes visited and unvisited links the same color, so each visitor gets nice clean blue links, not ones that other people have been thumbing through and staining purple.
! Disable drag-to-select. *hysteresis: 3000 ! Make visited and unvisited links the same color by default *linkForeground: #0000EE *vlinkForeground: #0000EE Netscape.Navigator.geometry: =NETSCAPE_GEOMETRY ! Disable some of the keyboard commands. *globalTranslations: ! Mouse bindings: make all mouse buttons do the same thing. *drawingArea.translations: #replace \ <Btn1Down>: ArmLink() \n\ <Btn2Down>: ArmLink() \n\ <Btn3Down>: ArmLink() \n\ ~Shift<Btn1Up>: ActivateLink() \ DisarmLink() \n\ ~Shift<Btn2Up>: ActivateLink() \ DisarmLink() \n\ ~Shift<Btn3Up>: ActivateLink() \ DisarmLink() \n\ Shift<Btn1Up>: ActivateLink() \ DisarmLink() \n\ Shift<Btn2Up>: ActivateLink() \ DisarmLink() \n\ Shift<Btn3Up>: ActivateLink() \ DisarmLink() \n\ <Btn1Motion>: DisarmLinkIfMoved() \n\ <Btn2Motion>: DisarmLinkIfMoved() \n\ <Btn3Motion>: DisarmLinkIfMoved() \n\ <Motion>: DescribeLink() \n\
You should replace the
NETSCAPE_GEOMETRY in this file
with an X geometry that looks like this:
X is the width of your screen and
is the height of your screen
+ 32. This will position
the Netscape menu bar off the top of the screen, so the user won't
be distracted. For example, if your screen is 800x600, the geometry
mkdir /home/guest/.netscape chmod 777 /home/guest/.netscape
.netscape directory and
make it world-writable.
Log out, then log in as
Since you won't be able to use the menu bar as
you should edit guest's preferences manually if you need to change
them, or change your own preferences to what you want
guest's to be and copy the preferences file.
Install RedHat (further just RH) Linux on the box. Make sure shadow and MD5 passwords are enabled. And have a nice long root password! Refer to corresponding installation guides.
RH Linux was and is *really* buggy out of the box (both local and remote exploits are discovered every day, see BugTRAQ database), and many software packages installed by default can be used to obtain root shell from non-privileged account or in the worst cases across the network (or just mess up the box). Thus special attention should be given to package selection on the browser workstation.
- Use workstation or custom installation mode. The latter is recommended, when selecting groups of packages, only choose base-system, networked workstation, mail/www services (make sure you later replace Communicator with Navigator) and X packages and then erase the unneeded RPMs. If using workstation mode you will have to (possibly manually) remove about 300 packages.
- When partitioning the disk follow the scheme below. The sizes
are appropriate for the 3 GB disk, scale the sizes accordingly for
bigger drive but this is really not needed for this setup as the
whole Linux system is squeezed to under 200MB. Make sure those
partitions (/,/home,/var and /tmp) are present! Separate
/usr is not necessary! Remember to create a generous swap partition
(at least the size of RAM).
Partitions mount points and sizes used for a test system:
Filesystem 1k-blocks Used Available Use% Mounted on /dev/hda1 1571528 184184 1307512 12% / /dev/hda7 300603 309 284773 0% /home /dev/hda6 300603 20 285062 0% /tmp /dev/hda5 809556 4640 763792 1% /var
- Remove all RPMs but those (list might be shortened later and
automatic RPM-removal shell script might be written as well)
MAKEDEV-2.5.2-1 SysVinit-2.78-5 X11R6-contrib-3.3.2-11 XFree86-100dpi-fonts-3.3.6-20 XFree86-3.3.6-20 XFree86-75dpi-fonts-3.3.6-20 XFree86-S3-3.3.6-20 XFree86-SVGA-3.3.6-20 XFree86-VGA16-3.3.6-20 XFree86-libs-3.3.6-20 XFree86-xfs-3.3.6-20 Xconfigurator-4.3.5-1 apmd-3.0final-2 ash-0.2-20 at-3.1.7-14 audiofile-0.1.9-3 authconfig-3.0.3-1 basesystem-6.0-4 bash-1.14.7-22 bc-1.05a-5 bdflush-1.5-11 binutils-188.8.131.52.22-6 bzip2-0.9.5d-2 chkconfig-1.1.2-1 chkfontpath-1.7-2 console-tools-19990829-10 cracklib-2.7-5 cracklib-dicts-2.7-5 crontabs-1.7-7 dev-2.7.18-3 diffutils-2.7-17 e2fsprogs-1.18-5 ed-0.2-13 eject-2.0.2-4 etcskel-2.3-1 file-3.28-2 filesystem-1.3.5-1 fileutils-4.0-21 findutils-4.1-34 freetype-1.3.1-5 gawk-3.0.4-2 gd-1.3-6 gdbm-1.8.0-3 getty_ps-2.0.7j-9 glib-1.2.6-3 glib10-1.0.6-6 glibc-2.1.3-15 gmp-2.0.2-13 gpm-1.18.1-7 grep-2.4-3 groff-1.15-8 gtk+-1.2.6-7 gzip-1.2.4a-2 hdparm-3.6-4 imlib-1.9.7-3 indexhtml-6.2-1 info-4.0-5 initscripts-5.00-1 iputils-20000121-2 isapnptools-1.21b-1 kbdconfig-184.108.40.206-1 kernel-2.2.14-5.0 kernel-utils-2.2.14-5.0 krb5-configs-1.1.1-9 krb5-libs-1.1.1-9 kudzu-0.36-2 ld.so-1.9.5-13 ldconfig-1.9.5-16 less-346-2 libc-5.3.12-31 libgr-2.0.13-23 libgr-progs-2.0.13-23 libjpeg-6b-10 libpng-1.0.5-3 libstdc++-2.9.0-30 libtermcap-2.0.8-20 libtiff-3.5.4-5 libungif-4.1.0-4 libxml-1.8.6-2 lilo-0.21-15 logrotate-3.3.2-1 losetup-2.10f-1 mailcap-2.0.6-1 man-1.5h1-1 mingetty-0.9.4-11 mkbootdisk-1.2.5-3 mkinitrd-2.4.1-2 mktemp-1.5-2 modutils-2.3.9-6 mount-2.10f-1 mouseconfig-4.4-1 ncompress-4.2.4-15 ncurses-5.0-11 net-tools-1.54-4 netscape-common-4.72-6 netscape-navigator-4.72-6 newt-0.50.8-2 ntsysv-1.1.2-1 pam-0.72-6 passwd-0.64.1-1 pciutils-2.1.5-2 popt-1.5-0.48 procps-2.0.6-5 psmisc-19-2 pwdb-0.61-0 raidtools-0.90-6 rdate-1.0-1 readline-2.2.1-6 redhat-logos-1.1.0-2 redhat-release-6.2-1 rootfiles-5.2-5 rpm-3.0.4-0.48 rpmfind-1.4-3 rxvt-2.6.1-8 sash-3.4-2 sed-3.02-6 setup-2.1.8-1 setuptool-1.2-5 sh-utils-2.0-5 shadow-utils-19990827-10 slang-1.2.2-5 slocate-2.1-2 stat-1.5-12 sysklogd-1.3.31-16 tar-1.13.17-3 tcl-8.0.5-35 tcp_wrappers-7.6-10 termcap-10.2.7-9 textutils-2.0a-2 time-1.7-9 timeconfig-3.0.3-2 tmpwatch-2.2-1 utempter-0.5.2-2 util-linux-2.10f-7 vixie-cron-3.0.1-40 which-2.9-2 words-2-12 xinitrc-2.9-1 xpm-3.4k-2 zlib-1.1.3-6
Install ssh-server RPM for remote administration. Do NOT use inetd daemon mode, make sshd run standalone and use /etc/hosts.allow for access control (ssh daemon will read the file upon startup)
Make sure you create a boot floppy using a mkbootdisk command as errors in LILO configuration might render the system unbootable.
Make the following modifications to configuration files
#=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- /dev/hda1 / ext2 defaults,ro 1 1 /dev/hda7 /home ext2 defaults,nodev,noexec,nosuid 1 2 /dev/hda6 /tmp ext2 defaults,nodev,noexec,nosuid 1 2 /dev/hda5 /var ext2 defaults,nodev,noexec,nosuid 1 2 #=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- #/dev/cdrom /mnt/cdrom iso9660 noauto,owner,ro 0 0 #/dev/fd0 /mnt/floppy auto noauto,owner 0 0 #=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- none /proc proc defaults 0 0 none /dev/pts devpts gid=5,mode=620 0 0 /dev/hda8 swap swap defaults 0 0 #=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
- For / : mounted read-only (ro), just to make it a little bit harder to do Bad Things
- For /home, /tmp and /var :
nodev,noexec,nosuid will prevent (a) starting executable
from them (download and run through netscape attack), (b)running
suid executables (well, redundant in presence of the above but nice
to have too) (c)creating devices by makedev (no faked /dev/mem for
kernel module attack)
Making /home read-only might be good idea too as no netscape is not supposed to write anything while running.
- Remember to REMOVE floppy and CDROM physically and disable partitions (commented out)!
Create file xbrowser in /etc/rc.d/init.d and symlink (
cd /etc/rc.d/rc4.d ; ln -s /etc/rc.d/init.d/xbrowser S99xbrowser)it as S99xbrowser in /etc/rc.d/rc4.d so that directory /etc/rc.d/rc4.d looks like this
drwxrwxrwx 2 root root 4096 Sep 10 15:30 . drwxrwxrwx 10 root root 4096 Sep 10 15:30 .. lrwxrwxrwx 1 root root 1179 Sep 10 15:30 S05kudzu-> ../init.d/kudzu lrwxrwxrwx 1 root root 5094 Sep 10 15:30 S10network-> ../init.d/network lrwxrwxrwx 1 root root 1367 Sep 10 15:30 S16apmd-> ../init.d/apmd lrwxrwxrwx 1 root root 1542 Sep 10 15:30 S20random-> ../init.d/random lrwxrwxrwx 1 root root 3217 Sep 10 15:30 S25netfs-> ../init.d/netfs lrwxrwxrwx 1 root root 1024 Sep 10 15:30 S30syslog-> ../init.d/syslog lrwxrwxrwx 1 root root 989 Sep 10 15:30 S40atd-> ../init.d/atd lrwxrwxrwx 1 root root 1031 Sep 10 15:30 S40crond-> ../init.d/crond lrwxrwxrwx 1 root root 1203 Sep 10 15:30 S75keytable-> ../init.d/keytable lrwxrwxrwx 1 root root 1261 Sep 10 15:30 S85gpm-> ../init.d/gpm lrwxrwxrwx 1 root root 1956 Sep 10 15:30 S90xfs-> ../init.d/xfs lrwxrwxrwx 1 root root 650 Sep 10 15:30 S99xbrowser-> ../init.d/xbrowser
xbrowser file looks like this
#!/bin/bash # --anton: Init the box into X with browser, no login script echo "Starting standalone browser....." #put a mark into log echo %%%%%%Reboot%%%%% >> /var/log/xlog #this file marks X startrup using out xinitrc touch /tmp/startOK #--main loop, indefinite with the presence of /tmp/startOK file ------------------ while [ -f /tmp/startOK ] ; do #put a mark into log echo %%%%%%Restart%%%%% >> /var/log/xlog #kill stuck netscape if any (this doesnt help if it turn zombie) killall -9 netscape >& /dev/null #clear netscape lock if [ -f ~netscape/.netscape/lock ]; then /bin/rm ~netscape/.netscape/lock fi #start X windows, no winman, using the config that starts only netscape #config is in root home dir!! #X server runs as root, sort of BAD /usr/X11R6/bin/xinit /root/.xinitrc -- /usr/X11R6/bin/X bc done #main loop end-------------------------------
- Make sure /etc/sysctl.conf looks like this
# Disables packet forwarding net.ipv4.ip_forward = 0 # Enables source route verification net.ipv4.conf.all.rp_filter = 1 # Disables automatic defragmentation (needed for masquerading, LVS) net.ipv4.ip_always_defrag = 0 # Disables the magic-sysrq key #--anton: this IS important kernel.sysrq = 0
Make changes to /etc/X11/XF86Config that was automatically created during install to look have those in:
# File generated by XConfigurator. ...whatever... # ********************************************************************** # Server flags section. # ********************************************************************** Section "ServerFlags" # Uncomment this to cause a core dump at the spot where a signal is # received. This may leave the console in an unusable state, but may # provide a better stack trace in the core dump to aid in debugging #NoTrapSignals # Uncomment this to disable the <Ctrl><Alt><BS> server abort sequence # This allows clients to receive this key event. #--anton -- no X server kill #--another option is to have a kill as a means to fight broken/stuck netscape, #--restart will bring it back after cleanup DontZap # Uncomment this to disable the <Crtl><Alt><KP_+>/<KP_-> mode switching # sequences. This allows clients to receive these key events. #--anton -- kinda bad too DontZoom EndSection ...whatever...
Make sure that /root/.xinitrc looks like
/bin/rm -f ~netscape/.netscape/lock >& /dev/null #--anton: otherwise non-root netscape cant run #--anton only allow local but from all users #--anton the name of test box was "afc" thus the line below xhost +afc #--anton:starts netscape as user "netscape" and full screen!! #make sure 1024x768 matches your monitor su netscape -c "netscape -no-about-splash -geometry 1024x768+0+0" #---------------TESTING--------------------------- #these commands were used in testing to set netscpae preferences #same as having "netscape" uiser home dir writable for this user #export HOME=/home/netscape #netscape -no-about-splash -geometry 1024x768+0+0 >& /tmp/LOG #---------------TESTING--------------------------- #also needed: X as user "guest" eventually
Create user netscape, his home directory will be /home/netscape.
Start netscape and apply a restricted settings as:
- no Java (known big risks, recently really big holes discovered in Netscape Java implementation),
- no cache (some Java bugs will access cache objects and then bypass JVM restrictions),
- no cookies (might not be possible though, low risk),
- remove all launches of nonstandard applications (ideally-all applications) with file types (by going to Netscape->Edit->Preferences->Navigator->Applications),
- history length set to 0 (next user can't see what previous was doing, the risk is in seeing URL-encoded passwords sometimes)
Do chown to root on /home/netscape (by
root.root /home/netscape). Make sure that his home directory
belongs to root, there are no world-writable files and
subdirectories there and permission are at least
/home/netscape/: total 9 drwxr-xr-x 4 root root 1024 Sep 7 18:29 . drwxr-xr-x 4 root root 1024 Sep 7 18:30 .. -rw-r--r-- 1 root root 16 Sep 7 18:29 .bash_history -rw-r--r-- 1 root root 24 Sep 5 08:21 .bash_logout -rw-r--r-- 1 root root 230 Sep 5 08:21 .bash_profile -rw-r--r-- 1 root root 124 Sep 5 08:21 .bashrc -rw-r--r-- 1 root root 93 Sep 7 18:25 .mailcap -rw-r--r-- 1 root root 0 Sep 7 18:25 .mime.types drwxr-xr-x 4 root root 1024 Sep 10 08:38 .netscape drwxr--r-- 2 root root 1024 Sep 6 00:04 .xauth /home/netscape/.netscape: total 264 drwxr-xr-x 4 root root 1024 Sep 10 08:38 . drwxr-xr-x 4 root root 1024 Sep 7 18:29 .. drwxr--r-- 2 root root 1024 Sep 6 00:04 archive -rw------- 1 root root 14757 Sep 7 18:38 bookmarks.html drwxr--r-- 3 root root 1024 Sep 7 18:24 cache -rw-r--r-- 1 root root 188416 Sep 6 00:05 cert7.db -rw-r--r-- 1 root root 16384 Sep 7 18:30 history.dat -rw-r--r-- 1 root root 111 Sep 7 16:20 history.list -rw-r--r-- 1 root root 16384 Sep 6 00:05 key3.db -rw-r--r-- 1 root root 0 Sep 6 00:04 nswrapper.copy_defs -rw-r--r-- 1 root root 279 Sep 10 08:38 plugin-list -rw-r--r-- 1 root root 3398 Sep 7 18:29 preferences.js -rw-r--r-- 1 root root 741 Sep 7 18:29 registry -rw-r--r-- 1 root root 16384 Sep 7 18:29 secmodule.db
Carefully test netscape functionality upon doing the chown to root! At present, I have not found a way to avoid periodic Netscape complaints about "Can't write preferences".
Another note is appropriate. Netscape is VERY buggy (last example is Red Hat Linux Security Advisory presents a way to crash and exploit netscape using a specially crafted JPEG image) and is likely to crash periodically, possibly producing a buffer overflow with shell access for the intruder. This shell will have the netscape user as owner. Thus the absence of xterm and rxvt on the system is absolutely crucial as it provides another line of defense. Permission on the system should also be set very conservatively (no world-writable files). Ideally, NO files should be owned by user "netscape" on the system AT ALL (do a find / -user netscape command to confirm this, also check for world writable files with find / -perm -2 ! -type l -ls).
The word restricted will cause password prompting in order to enter non-standard runlevel (e.g. linux init 0 from LILO: prompt).
boot=/dev/hda map=/boot/map install=/boot/boot.b prompt timeout=50 default=linux image=/boot/vmlinuz-2.2.14-5.0 label=linux read-only root=/dev/hda1 restricted
That implies using stock RH 6.2 kernel. Kernel upgrade to 2.2.16 might be a good idea as some bugs were found in early 2.2.14 kernels (low risk).
REMOVE /usr/X11R6/bin/xterm xterm executable COMPLETELY! This is REALLY IMPORTANT as shell will be much harder to obtain in this case. Make sure its clone, rxvt, is not installed! Ideally, all programs that can spawn a shell should be removed.
Some physical security
- Secure reset button
- Remove CDROM and floppy disk drive
- Prevent access to the box to avoid hard drive replacement
Some final touches (nice but not essential for system functionality)
- Implement free disk space monitor top avoid partition overflows
- Enable remote logging (preferably to some dedicated box with host-based IDS that analyzes the logs)
It just might work ;-)
- Web Kiosk HOWTO Similar HOWTO, main differences: no keyboard, uses fvwm2
- Public Web Browser HOWTO Similar HOWTO, older and less security oriented
- Security HOWTO Linux Security HOWTO
- NIC Site You can buy something similar to what is described in the HOWTO for $199 (I am not affiliated with the company in any way)
- http://www.chuvakin.org/ispdoc I also maintain a Linux ISP HOWTO.
- http://www.chuvakin.org/books I also maintain a list of computer/network security related books with (where available) reviews and online availability. If you have a book that I don't list please use the form on the page and I will add it to the list and maybe review it later.