doc:howto:secure.access

Secure your router's access

There are some possibilities to grant access to the router (or to any PC/Server): ask for nothing: anybody who can establish a connection gets access ask for username and password on an unsecured connection (e.g. telnet) ask for username and password on an encrypted connection (e.g. SSH) (e.g. by following firstlogin signature instead of a password (e.g. SSH with ask for username and merely ainstead of a(e.g. SSH with signature.authentication If you ask for username/password, an attacker has to guess the combination. If you use an unencrypted connection, he could eavesdrop on you and obtain them. If you use an encrypted connection, any eavesdropper would have to decrypt the packets first. This is always possible. How long it takes to decrypt the content, depends on the algorithm and key length you used. Also, as long as an attacker has network access to the console, he can always run a brute-force attack to find out username and password. He does not have to do that himself: he can let his computer(s) do the guessing. To render this option improbable or even impossible you can: not offer access from the Internet at all, or restrict it to certain IP addresses or IP address ranges by letting the SSH server dropbear and the web-Server uhttpd not listen on the external/WAN port by blocking incoming connections to those ports (TCP 22, 80 and 443 by default) in your firewall make it more difficult to guess: don't use the username root don't use a weak password with 8 or less characters don't let the SSH server dropbear listen on the default port (22) use the combination of username different than root dropbear to listen on a random port (should be >1024): System → Administration → Dropbear Instance → Port tellto listen on a random port (should be >1024): System → Administration → Dropbear Instance → Port public key authentication. Your public keys can be specified in Administation → System → SSH-keys. An older guide to DropBear SSH public key authentication has detailed information on generating SSH keypairs which include the public key(s) you should upload to your configuration.

System Hardening

If you have an external disk you may want to encrypt it.

Network hardening

Create a non-privileged user in OpenWrt

Example that adds a user called nicolaus: opkg update opkg install shadow-useradd useradd nicolaus Or add the user by hand (Take care that uid/gid (e.g.=1000) are not already in use!) /etc/passwd: USER:x:1000:1000:GROUP:/mnt/usb:/bin/false /etc/group: GROUP:x:1000: /etc/shadow: USER:RANDOMSTUFWillBeUpdatedWithPasswd:16666:0:99999:7::: passwd USER However, you can't ssh to this user yet. To enable ssh access, you should make a password for that user, create his home folder and most importantly indicate the shell of that user: passwd nicolaus mkdir /home mkdir /home/nicolaus chown nicolaus /home/nicolaus vi /etc/passwd nicolaus:x:1000:1000:nicolaus:/home/nicolaus:/bin/ash Or add the user by hand (Take care that(e.g.=1000) are not already in use!)However, you can't ssh to this user yet. To enable ssh access, you should make a password for that user, create his home folder and most importantlyof that user:

Allow temporary privileged access using sudo

First, you should install sudo : opkg install sudo Additionally, you must allow your desired user by manipulating '/etc/sudoers ' by tool visudo . Now you can follow ONE of the methods below to choose how the user should be able to run commands as root : Additionally, you must allow your desired user by manipulating' by tool. Now you can followof the methods below to choose how the user should be able to run commands as

Method 1: 'sudo'ing by any user with root password (more secure)

In this method any user can temporarily run commands as root only if he knows the root password. This way when the user runs a command with sudo he should enter root's password instead of his password. For enabling this method you should open the file '/etc/sudoers ' by entering the command visudo Then uncomment the 2 lines below in that file and then save ## Uncomment to allow any user to run sudo if they know the password ## of the user they are running the command as (root by default). Defaults targetpw # Ask for the password of the target user ALL ALL=(ALL) ALL # WARNING: only use this together with 'Defaults targetpw' This method is more secure because you don't need to protect both root and privileged (sudoer) users to keep the whole system safe. Then uncomment the 2 lines below in that file and then saveThis method is more secure because you don't need to protect both root and privileged (sudoer) users to keep the whole system safe. One usecase can be allowing remote ssh with password from WAN: For more security (still less than RSA key) you can only allow users other than root to ssh with their password (optionally on a custom port) from WAN. And for even more security you can request root's password after running sudo . Therefor in this scenario a hacker should find 3 different strings user's username, user's password and root's password to get full access to the system. Even if the user's account get compromised, then the intruder still can't damage your system because he doesn't have root password yet.

Method 2: 'sudo'ing with the user's password

In this method, after logging in by the desired user, when you enter sudo you should enter the user's password again. The end result is similar to how you use sudo in Ubuntu or other popular Linux disros, but this method doesn't utilize group 'sudo' for this purpose. For enabling this method you should also enter the command visudo And then add a line allowing your user, under comment "## User privilege specification": ## ## User privilege specification ## root ALL=(ALL) ALL nicolaus ALL=(ALL) ALL And then add a line allowing your user, under comment "## User privilege specification":

Method 3: 'sudo'ing with the user's password if he is member of group 'sudo' (needs installing some packages)

This method is very similar to Method 2, except that it allows any member of group 'sudo' to use sudo with their own password. This method is exactly the same one used in Ubuntu and other popular Linux distros to allow 'sudo ' access for a user. For activating this method first you should allow group 'sudo' to use command sudo by entering visudo And then uncomment the line below: ## Uncomment to allow members of group sudo to execute any command %sudo ALL=(ALL) ALL Second you should create group 'sudo'. You can do it by manually editing '/etc/group ' but it's more standard to install and use tools for this purpose: opkg install shadow-groupadd groupadd --system sudo And finally add your current user to the group 'sudo'. You can directly append your user to '/etc/group ' but again it's better to use usermod : opkg install shadow-usermod usermod -a -G sudo nicolaus This method is more convenient because you can simply allow sudo access for any user you want, just by usermod -a -G sudo <USER> but takes more space (for installing new packages) than method 2 which may be more suitable for systems with very limited space.

ppp

If you are using ppp in the default configuration with username and password in /etc/config/network , then the unprivileged user can read it from pppd's command line (with e.g. ps w ). To prevent that, you can add " user <username> " to /etc/ppp/options and " <username> * <password> " to /etc/ppp/{chap|pap}-secrets and then remove the username / password options from uci configuration. Of course /etc/ppp/{chap|pap}-secrets should not be world readable: chmod go-rw /etc/ppp/chap-secrets

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