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README.Debian
fail2ban (>=0.7.0) for Debian ----------------------------- This package is ~99% identical to the upstream version. Few features could have been added but not yet propagated into upstream version and some modifications might be Debian-specific. Debian specific jail.conf file is shipped. Original upstream file is available from /usr/share/doc/fail2ban/examples/jail.conf Currently, the major difference with upstream: python libraries are placed under /usr/share/fail2ban instead of /usr/lib/fail2ban to comply with policy regarding architecture independent resources. Upgrade from 0.6 versions: ------------------------- * New Config Files Format: If you had introduced your own sections in /etc/fail2ban.conf, you would need manually to convert them into a new format. At minimum you need to create /etc/fail2ban/filter.d/NAME.local (leave .conf files for me and upstream please to avoid any conflicts -- introduce your changes in .local) with failregex in [Definition] section. And provide appropriate jail definition in /etc/fail2ban/jail.local * Enabled Sections: Only handling of ssh files is enabled by default. If you want to use fail2ban with apache, please enable apache section manually in /etc/fail2ban/jail.local by including next lines: [apache] enabled = true NOTE: -e command line parameter is non existent in 0.7.x * Interpolations vs actions/filters parameters: For details see #398739 or wait for a closure of #400416 Every pair of .conf and then .local (if exists) files is read separately from any other configuration file, so interpolations cannot penetrate from jail.* into actions.d/*. To overcome this, it is necessary to create a PARAMETER which can be substituted in actions [Definition] section, if it is also defined in the [Init] section of that file and is used in place of necessary allocation as <PARAMETER> tag. Parameters can be specified in the definitions within jail.{conf,local}. For instance, 1 lengthy example, where the same name "fwchain" is used both as interpolation (in jail.local) and as a parameter (in iptables-flex.local) (from #398739) ==> /etc/fail2ban/jail.local <== [DEFAULT] action = iptables-flex[name=%(__name__)s, port=%(port)s, fwchain=%(fwchain)s, post_start_commands=%(post_start_commands)s, pre_end_commands=%(pre_end_commands)s] fwchain = INPUT [ssh] fwchain = ssh-tarpit ==> /etc/fail2ban/action.d/iptables-flex.local <== [Definition] actionstart = iptables -N fail2ban-<name> iptables -I <fwchain> -m state --state NEW -p <protocol> --dport <port> -j fail2ban-<name> iptables -I <fwchain> -j <whitelist> actionstop = iptables -D <fwchain> -j <whitelist> iptables -D <fwchain> -m state --state NEW -p <protocol> --dport <port> -j fail2ban-<name> iptables -F fail2ban-<name> iptables -X fail2ban-<name> actioncheck = iptables -n -L <fwchain> | grep -q fail2ban-<name> actionban = iptables -I fail2ban-<name> 1 -s <ip> -j DROP actionunban = iptables -D fail2ban-<name> -s <ip> -j DROP [Init] whitelist = ssh-whitelist fwchain = INPUT name = default port = ssh protocol = tcp * Multiport banning: Comment for #373592, #545971 iptables-multiport action is now default banaction (file jail.conf, to be customized within jail.local). Therefore assure that you have built multiport module if you use custom kernel. If you would like to ban all ports for that host, just redefine fwban/fwunban commands to don't have --dport %(port)s statement at all, or use shorewall, where actionban bans whole IP. * Blocking of NEW connections only Comment for the wishlist #350746. It might be benefitial in some cases to ban only new connections. For that just use iptables-new action instead of default banaction /etc/fail2ban/jail.local: [DEFAULT] banaction=iptables-new (you can override banaction within interesting for you section). Also you can redefine the whole action parameter if you like. * Interaction with ipmasq Comment to #461417 Although fail2ban should detect and recreate missing chains if the external command wipes out iptables, it is better to explicitly to force-reload fail2ban. For this reason there is examples/ipmasq-ZZZzzz|fail2ban.rul file is shipped along to be installed under name ZZZzzz|fail2ban.rul within /etc/ipmasq. * Interaction with logrotate with custom logtarget Comment to #631917 if you use an alternative logtarget (e.g. SYSLOG) thus not using /var/log/fail2ban.log you should divert logrotate configuration into a disabled state, e.g. sudo dpkg-divert --rename --divert \ /etc/logrotate.d/fail2ban.disabled /etc/logrotate.d/fail2ban Troubleshooting: --------------- * Updated failregex: To resolve the security bug #330827 [1] failregex expressions must provide a named group (?P<host>...) as a placeholder of the abuser's host. Alternative tag (since 0.7.5) can be "<HOST>". The naming of the group was introduced to capture possible future generalizations of failregex to provide even more information. [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=330827 You might benefit from using fail2ban-regex command shipped along to construct and debug your failregex statements. * "Interpolations" in the config file: Since version 0.6.0-3 to reduce duplication, thus to improve readability of the config file, interpolations provided by the module ConfigParser are used. If you had custom sections defined before, you might benefit from updating config file and adding appropriate information for the new sections. N.B. If you have some nice additional sections defined, I would really appreciate if you share them with me or upstream author, so they could be eventually included in the fail2ban package for general use by the rest of the community. * Mailing: Since actions.d/mail*.conf commands rely on presence of "mail" command, mailx package (or another package providing mailx functionality such as mailutils) is required if those actions are activated in jail.{conf,local}. * Dirty exit: If firewall rules gets cleaned out before fail2ban exits (like was happening with firestarter), errors get reported during the exit of fail2ban, but they are "safe" and can be ignored. ** SSHD Configuration Specific Problems * Ban "Not allowed" attempts: Make sure that you have ChallengeResponseAuthentication no PasswordAuthentication yes Details from the bug report #350980 [2] [2] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=350980 * Not caught attempts to login as root On the boxes running older versions of openssh (e.g. sarge distribution) in the case when PermitRootLogin is set to something else than "yes" and iff AllowUsers is active, failed root logins do not confirm to the standard logging message -- they omit the source IP, thus allowing attack to persist since such messages are not caught by fail2ban. * Bantime: An IP is banned for "bantime" not since the last failed login attempt from the IP, but rather since the moment when failed login was detected by fail2ban. Thus, if fail2ban gets [re]started, any IP which had enough of failed logins with durations less than "findtime" between them prior to the [re]start moment, will be banned for "bantime" since [re]start moment, not since the last failed login time. * Findtime: "Findtime" option of a jail actually defines a duration to reset the counter of failed login attempts, if no new attempt was detected within that time frame (i.e. within "findtime"). See http://www.fail2ban.org/wiki/index.php/MANUAL_0_8#Jail_Options for more information on jail options. * Syslog entries can be 'forged' by a regular user From http://www.fail2ban.org/wiki/index.php/MANUAL_0_8#Possibility_of_DOS_attack_by_a_local_user Especially on systems which provide ssh/CGI/PHP services to unknown users it is possible to block other users from ssh and probably other access as a unprivileged user may issue: logger -p auth.warning -t 'sshd[123]' 'Illegal user user1 from 1.2.3.4' N.B. chmod o-x /usr/bin/logger should provide at least obfuscation solution Or the malicious user may write via PHP's openlog()/syslog() to syslog. P.S. Anyone is welcome to recommend proper security solution to this issue, such as an alternative to sysklogd which allows better control over users logging to specific facilities (such as AUTH) -- Yaroslav Halchenko <debian@onerussian.com>, Fri, 15 Jul 2016 08:59:10 -0400