# Red Hat Security: Linux in Physical, Virtual and Cloud (RH415) _Last update: Mon Nov 18 05:32:46 UTC 2019 by [@luckylittle](https://github.com/luckylittle)_ --- ## 1. Managing Security & Risk ```bash # USING YUM TO MANAGE SECURITY ERRATA: yum updateinfo --security # security related updates/summary yum updateinfo list updates | grep Critical # identify critical RHSAs yum updateinfo RHSA-2018:1453 # view RHSA details and corresponding CVEs yum updateinfo list --cve CVE-2018-1111 # what needs to be updated to fix CVE yum update --cve CVE-2018-1111 # resolve CVE yum list updates --security # how many security updates are there? ``` ```bash # SECURING SERVICES: ss -tlw # open ports in the listening state # CUSTOMIZING YOUR SSH SERVICE CONFIGURATION: vi /etc/ssh/sshd_config PermitRootLogin no # do not allow root to SSH to this machine PasswordAuthentication no # force only key-based authentication # ALLOW/DENY USERS & GROUPS: # The allow/deny directives are processed in the following order: DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups. If specified, login is allowed ONLY for usernames that match one of the patterns! AllowUsers root@192.168.22.* # this would need PermitRootLogin yes AllowUsers James@host1.example.com AllowUsers root@192.168.22.0/24 James@host1.example.com AllowGroups wheel # If all of the criteria on the Match line are satisfied, the keywords on the following lines override those set in the global section of the config file, until either another Match line or the end of the file. The available criteria are User, Group, Host, LocalAddress, LocalPort, and Address: Match Address 192.168.0.? # 192.168.0.[0-9] network range PermitRootLogin yes systemctl reload sshd # SSH key filesystem permissions: ~/.ssh/ # 0700 ~/.ssh/id_rsa.pub # 0644 ~/.ssh/id_rsa # 0600 ``` ```bash # SUDO: su # switches to the target user (which is root by default), but provides a normal shell with the same environment as the user who invoked the su command su - # switches to the target user and invokes a login shell based on the target user's environment. A login shell resets most environment variables, including the target user's PATH visudo vi /etc/sudoers Defaults timestamp_timeout = 1 # require password every minute (0 = every time it's used) User_Alias FULLTIMERS = millert, mikef, dowdy Runas_Alias OP = root, operator Host_Alias SERVERS = master, mail, www, ns Cmnd_Alias REBOOT = /usr/sbin/reboot root ALL = (ALL) ALL # who where = (as_whom) what %wheel ALL = (ALL) ALL # we let any user in group wheel run any command on any host as any user FULLTIMERS ALL = NOPASSWD: ALL lisa SERVERS = ALL bob SERVERS = (OP) ALL : 128.138.242.0 = (OP) REBOOT # the user bob may run anything on the SERVERS and can run reboot on 128.138.242.0 machines as any user listed in the OP Runas_Alias (root and operator) sudo # resets the PATH variable based on the 'secure_path' directive in the /etc/sudoers file sudo -i # changes to the root user's home directory and opens an interactive login shell based on the root user's environment variables ``` ## 2. Automating Configuration & Remediation with Ansible ```bash # This chapter is not covered in large detail as it is part of a different document # An example of a typical 'ansible.cfg' file: [defaults] inventory = ./inventory remote_user = user ask_pass = false [privilege_escalation] become = true become_method = sudo become_user = root become_ask_pass = false ``` ```bash # Ansible role for SELinux remediation (yum install rhel-system-roles): linux-system-roles.selinux ``` ## 3. Protecting Data with LUKS & NBDE ```bash # CREATION OF ENCRYPTED DEVICES AT INSTALLATION USING KICKSTART: autopart --type=lvm --encrypted --passphrase=PASSPHRASE # use automated partitioning part /home --fstype=ext4 --size=10000 --onpart=vda2 --encrypted --passphrase=PASSPHRASE part pv.01 --size=10000 --encrypted --passphrase=PASSPHRASE # encrypting an LVM physical volume ``` ```bash # ENCRYPTING DEVICES WITH LUKS AFTER INSTALLATION: parted -l # lists partition layout on all block devices parted /dev/vdb mklabel msdos mkpart primary xfs 1M 1G # msdos label type, primary xfs type partition from 1M to 1G (or use fdisk) parted /dev/vdb print cryptsetup luksFormat /dev/vdb1 [--key-file /path/to/file] # this will encrypt the drive cryptsetup luksDump /dev/vdb1 cryptsetup luksOpen /dev/vdb1 example # this will decrypt the drive ls /dev/mapper/example mkfs.xfs /dev/mapper/example mount -t xfs /dev/mapper/example /encrypted umount /encrypted cryptsetup luksClose example cryptsetup luksAddKey --key-slot 1 /dev/vdb1 # enter original passhphrase (or key-file) and the new passphrase cryptsetup luksChangeKey /dev/vdb1 # change passphrase ``` ```bash # NBDE - UNATTENDED DEVICE DECRYPTION AT BOOT TIME: # Servers: yum -y install tang # Tang servers validate the keys systemctl enable tangd.socket --now # tangd service binds to the 80/TCP port firewall-cmd --zone=public --add-service=http --permanent ; firewall-cmd --reload cd /var/db/tang # cryptographic keys are generated at first start jose jwk gen -i '{"alg":"ES512"}' -o signature.jwk # creating new keys manually jose jwk gen -i '{"alg":"ECMR"}' -o exchange.jwk # creating new keys manually mv -v gxB7oqYiEu3zrLay.jwk .gxB7oqYiEu3zrLay.jwk # rename both old keys to have leading period mv -v k25k6PbmgUu-pWWUb210x.jwk .k25k6PbmgUu-pWWUb210x.jwk # Clients: yum install clevis clevis-luks clevis-dracut # Clevis clients reach out to tang servers clevis luks bind -d /dev/vda1 tang '{"url":"http://demotang.lab.example.com"}' luksmeta show -d /dev/vda1 # verify that Clevis key was placed in LUKS header dracut -f # enable Dracut to unlock encrypted partitions using NBDS, takse a while systemctl enable clevis-luks-askpass.path # when decrypting non-root file system, needs clevis-dracut ``` ```bash # PERSISTENTLY MOUNTING LUKS FILE SYSTEMS: cat /etc/crypttab decrypted1 /dev/vdb1 none _netdev decrypted2 UUID=43d8995e-b876-4385-b124-7e402446d6c7 none _netdev cat /etc/fstab /dev/mapper/decrypted1 /encrypted xfs _netdev 1 2 ``` ```bash # SSS policy which defines three Tang servers, and requires at least two of them to be available for automatic decryption to occur cfg=$'{"t":2,"pins":{"tang":[\n > {"url":"http://demotang1.lab.example.com"},\n > {"url":"http://demotang2.lab.example.com"},\n > {"url":"http://demotang3.lab.example.com"}]}}' clevis luks bind -d /dev/vdb1 sss "$cfg" ``` ```json # JSON format of the above cfg example, do not forget HTTP and quotes: { "t": 2, "pins": { "tang": [ { "url": "http://demotang1.lab.example.com" }, { "url": "http://demotang2.lab.example.com" }, { "url": "http://demotang3.lab.example.com" } ] } } ``` ## 4. Restricting USB Device Access ```bash # USBGUARD: yum -y install usbguard yum -y install usbutils udisks2 # provides lsusb, udisksctl (shows serial num + blk device) rpm -qd usbguard # document files for a package rpm -qc usbguard # shows all config files for a package usbguard systemctl start usbguard ^start^enable # this will run the previous command and replace the string usbguard generate-policy > /etc/usbguard/rules.conf # authorizes the currently connected USB devices systemctl restart usbguard usbguard list-rules # Rule output example: 1: allow id 1d6b:0002 serial "0000:00:04.7" name "EHCI Host Controller" hash "CsKOZ6IY8v3eojsc1fqKDW84V+MMhD6HsjjojcZBjSg=" parent-hash "qiR4Ubbd7AIXLCz201hJYzaO9KIrOvqqRgqs2vM2NOY=" with-interface 09:00:00 ``` ```bash # AUTHORIZING A DEVICE TO PERSISTENTLY INTERACT WITH THE SYSTEM: usbguard list-devices # if a new USB device is attached to the system after the default policy is generated it is not authorized to access the system and is assigned a block rule target usbguard allow-device 6 # will not persist across reboots usbguard allow-device -p 6 # will add it to /etc/usbguard/rules.conf and persist systemctl restart usbguard # when rule is added, either reboot the machine or this usbguard list-devices usbguard list-devices --blocked # only show blocked usbguard list-rules usbguard watch # watch terminal for IPC activity ``` ```bash # PREVENTING A DEVICE FROM INTERACTING WITH THE SYSTEM, WHITE/BLACKLISTING: usbguard block-device # set its rule target to block usbguard list-devices --blocked usbguard reject-device # set its rule target to reject usbguard generate-policy -X -t reject \ # -X = don't generate hash attribute for devices > /etc/usbguard/rules.conf # generate a new base policy with a reject rule target that will ignore any additional USB devices that'll try to interact with the system grep usbguard /etc/group # 'groupadd usbguard' & 'usermod -aG usbguard richard' if needed (who can modify policy) vi /etc/usbguard/usbguard-daemon.conf RuleFile=/etc/usbguard/rules.conf # do not edit this file directly, but rather elsewhere and then move it here (sudo install -m 0600 -o root -g root modified_rules.conf /etc/usbguard/rules.conf ; systemctl restart usbguard) IPCAccessControlFiles=/etc/usbguard/IPCAccessControl.d/ IPCAllowedGroups=usbguard usbguard add-user -g usbguard --devices=modify,list,listen --policy=list --exceptions=listen # RULE OPTIONS: # man usbguard-rules.conf allow/reject name serial via-port hash with-interface # RULE OPERATORS (via-port {...}, with-interface {...}): all-of # must contain all specified values to match one-of # must contain at least one none-of # must not contain any equals # must contain exactly the same equals-ordered # must contain exactly the same also in the same order # RULE CONDITIONS: localtime(time_range) # true if local time is in the range allowed-matches(query) # true if device matches query rule-applied # true if rule currently being evaluated ever matched device before rule-applied(past_duration) # same as above, but if it matched devce in the past duration of time rule-evaluated # true if was ever evaluated before rule-evaluated(past_duration) # same as above, but if it was evaluated in the past duration of time random # probability is 0.5 by default, can be changed by p_true true false ``` ```bash # CREATING POLICIES THAT MATCH A SPECIFIC DEVICE: allow 1050:0011 name "Yubico Yubikey II" serial "0001234567" via-port "1-2" hash "044b5e168d40ee0245478416caf3d998" reject via-port "1-2" # allow Yubikey on a specific port, reject all other devices on that port # CREATING POLICIES THAT MATCH MULTIPLE DEVICES `{ interface class:subclass:protocol }`: allow with-interface equals { 08:*:* } # allow USB mass storage devices (class 08), deny all other via implicit rule reject # this at the end will block everything (catch-all) # REJECT DEVICES WITH SUSPICIOUS COMBINATION OF INTERFACES: allow with-interface equals { 08:*:* } reject with-interface all-of { 08:*:* 03:00:* } reject with-interface all-of { 08:*:* 03:01:* } reject with-interface all-of { 08:*:* e0:*:* } reject with-interface all-of { 08:*:* 02:*:* } # this whole block allows keyboard-only USB if there's not one already plugged # APPLY THE POLICY CHANGES: install -m 0600 -o root -g root ~/rules.conf /etc/usbguard/rules.conf ; systemctl restart usbguard ``` ## 5. Controlling Authentication with PAM ```bash # DESCRIBING THE PAM CONFIGURATION FILE SYNTAX: # Application configuration files in /etc/pam.d/ follow a standard format for their rules - parsed and executed top to bottom: type control module [module arguments] # 'type' can only be auth, account, password, session - in this order # 'control' is usually just required, requisite, sufficient, optional, include, substack # A dash (-) character in front of a type (such as "-session" near the end of the /etc/pam.d/system-auth file) indicates to silently skip the rule if the module file is missing. # PAM looks for the modules in the /usr/lib64/security/ directory. man -k pam_ | grep # e.g.: man pam_faildelay # USING SSSD AND PAM: yum -y install sssd authconfig --enablesssd --enablesssdauth --update # don't forget to put both here (sssd & sssd auth) ``` ```bash # PREPARING FOR CONFIGURATION UPDATE: authconfig --savebackup=/root/pambackup authconfig --restorebackup=/root/pambackup # restore process doesn't remove the links to your *-local files. It only restored the *-ac files and preserved your custom modifications. # authconfig modifies only the *-ac files (/etc/pam.d/system-auth-ac and /etc/pam.d/password-auth-ac) # most of the PAM service configuration files include the system-auth and password-auth files, which are symlinks to *-ac files # ensure that a secondary root shell is open at all times to recover from potential errors ``` ```bash # ONLY ALLOWING MANUAL CONFIGURATION: cd /etc/pam.d cp system-auth-ac system-auth-local # Make a copy of the existing system-auth-ac cp password-auth-ac password-auth-local # ...and password-auth-ac files to use for manual configuration rm system-auth password-auth # Remove the symbolic links ln -s system-auth-local system-auth # Recreate the links to point to your custom system-auth-local and password-auth-local files ln -s password-auth-local password-auth # now you can edit the custom system-auth-local and password-auth-local files without risking an overwrite by authconfig # ALLOWING BOTH MANUAL AND AUTHCONFIG CONFIGURATION: cd /etc/pam.d cp system-auth-ac system-auth-local # Make a copy of the of the existing system-auth-ac cp password-auth-ac password-auth-local # ...and password-auth-ac files to use for manual configuration rm system-auth password-auth # Remove the symbolic links ln -s system-auth-local system-auth # Recreate the links to point to your custom system-auth-local and password-auth-local files ln -s password-auth-local password-auth vi /etc/pam.d/system-auth-local # In your custom files, include the *-ac files auth include system-auth-ac account inlcude system-auth-ac password inlcude system-auth-ac session include system-auth-ac vi /etc/pam.d/password-auth-local auth include password-auth-ac account inlcude password-auth-ac password inlcude password-auth-ac session include password-auth-ac # you can now use the custom *-local files for manual configuration, but include the *-ac files for the configuration you do through authconfig ``` ```bash # DESCRIBING THE PAM_PWQUALITY MODULE: # man pwquality.conf authconfig --passminlen=12 --update grep pam_pwquality /etc/pam.d/system-auth /etc/pam.d/password-auth # these can be only specified in /etc/pam.d/ files: try_first_pass local_users_only retry authtok_type vi /etc/security/pwquality.conf # negative values indicate/enforce the minimum number of characters required for each class, zero means zero extra credit - but one credit still applies! Beware of defaults (commented out) minlen = 8 # passwords must be a minimum of eight characters in length [default=9] lcredit = 0 # policy does not specify anything regarding lowercase characters [default=1] ucredit = -1 # passwords must contain at least one uppercase character [default=1] dcredit = -2 # passwords must contain at least two digits [default=1] ocredit = -1 # passwords must contain at least one other/special character [default=1] ``` ```bash # PAM_TIME MODULE: # man time.conf vi /etc/security/time.conf # configure the pam_time module, syntax: services;ttys;users;times sshd|login;*;!root&student;Al1800-2300 # users can only log in using SSH or the console between 6PM and 11PM on any given day. This restriction does not apply to root and student - they will be able to log in at any time login;tty*&!ttyp*;!root;!Al0000-2400 # all users except for root are denied access to console-login at all times games;*;!waster;Wd0000-2400|Wk1800-0800 # games (configured to use PAM) are only to be accessed out of working hours. This rule does not apply to the user waster # PAM_ACCESS MODULE: # man access.conf authconfig --help | grep access authconfig --enablepamaccess --update # enables pam_access (check /etc/security/access.conf during account authorization) vi /etc/security/access.conf # syntax: permission:users/groups:origins +:root student: ALL # root and student users can log in from anywhere +:(operators):172.25.250.254 # members of the operators group can only log in if they attempt access from workstation (172.25.250.254) -:ALL EXCEPT (wheel) shutdown sync:LOCAL # disallow console logins to all but the shutdown, sync and all other accounts, which are a member of the wheel group -:ALL:ALL # other users are not allowed to log in ``` ```bash # LOCKING ACCOUNTS WITH MULTIPLE FAILED LOGINS: # man pam_faillock authconfig --help | grep faillock authconfig --enablefaillock --faillockargs="deny=3 fail_interval=60 unlock_time=600" --update faillock # list failed login attempts faillock --user user1 # restricts the output to a specific account faillock --user user1 --reset # removes the failure records for a user, as a side effect this also unlocks the account if it was locked authconfig --disablefaillock --update ``` ```bash # The 'pam_sepermit' module allows or denies login depending on SELinux enforcement state. When the user which is logging in matches an entry in the config file he is allowed access only when the SELinux is in enforcing mode: vim /etc/security/sepermit.conf lmaly:ignore @wheel:exclusive %guest_u:exclusive %staff_u:ignore %user_u:ignore ``` ## 6. Recording System Events with Audit ```bash # CONFIGURE CLIENT: /etc/audit/auditd.conf # main config file log_file # location of the log file, /var/log/audit/audit.log by default max_log_file # trigger max_log_file_action when file reaches X MB max_log_file_action # ROTATE (based on num_logs) or KEEP_FILES (ignore num_logs) num_logs # keep number of X old logs space_left # when X MB is remaining, space_left_action is triggered space_left_action # SYSLOG, EMAIL (see action_mail_acct), EXEC /path/to/script admin_space_left # when the file system containing the log file has this much free space (in MB) remaining admin_space_left_action # SUSPEND (auditd to stop writing audit records to the file system), SINGLE, HALT disk_full_action # SUSPEND, SINGLE (putting the system in single-user mode, allowing the admin to recover), HALT disk_error_action # SUSPEND, SINGLE, HALT (complete system shutdown) flush = INCREMENTAL_ASYNC # enable asynchronous flushing of records to storage after the number of writes specified by freq, DATA, SYNC freq = 50 # set the freq parameter to 50 to flush the Audit log after every 50 records log_format = ENRICHED # resolve UID, GID, system call number, architecture, and socket address information to names before transmitting each event name_format = HOSTNAME # include the machine's host name in each message /etc/audisp/plugins.d/syslog.conf # if you are sending messages to rsyslog active = yes # + you also need to configure /etc/rsyslog.conf yum install audispd-plugins # if you are sending messages to a remote auditd service /etc/audisp/plugins.d/au-remote.conf # needed for remote auditd active = yes /etc/audisp/audisp-remote.conf # needed for remote auditd, see man audisp-remote.conf for encryption remote_server # directive set to the IP address or host name of the remote auditd server port # if your remote server is not listening on the default 60/TCP port /etc/audit/audit.rules # do not edit this, it is automatically generated from the /etc/audit/rules.d/ /etc/audit/rules.d # all files ending in *.rules are combined into /etc/audit/audit.rules by augenrules systemctl status auditd; systemctl is-enabled auditd # CONFIGURE SERVER COLLECTING AUDITD EVENTS: /etc/rsyslog.conf # imudp or imtcp /etc/audit/auditd.conf tcp_listen_port = 60 # uncomment this line firewall-cmd --add-port=60/tcp --permanent ; firewall-cmd --reload systemctl restart auditd ; reboot ``` ```bash # INTERPRETING AUDIT MESSAGES: ausearch -i -a 28708 # show all records for the event that has 28708 as its event ID, interpret the log records - translate numeric values into names ausearch -f /path/to/file # search for all events related to a specific filename ausearch -m LOGIN --format csv > results.csv # search for all audit events of the LOGIN type, and export them in CSV format aureport -l # report logins aureport --summary # number of failed logins, authentications, failed authentications, users, AVCs etc. aureport -x # executable name report aureport -if /some/other/audit.log --executable --summary # show executable summary for the different auditd log file # TRACING A PROGRAM: # autrace command removes any active audit rules or requires you to remove any active rules before you run it autrace /bin/date # investigate the system calls performed by a process /bin/date, you can locate the records with PID ausearch --raw -p 26472 | aureport --file -i # PID from the previous autrace command ``` ```bash # SETTING SYSTEM CALL RULES: # when Audit starts, it assigns an Audit UID of 4294967295 to any existing process (-F auid!=4294967295) auditctl -l # list the current rules auditctl -s # current status of audit auditctl -a exit,always -F arch=b32 -F auid>=500 -S rename\ # audit the 32-bit version of both the rename and renameat system call for all users whose original Audit user ID is equal to or greater than 500 -S renameat -F subj_type!=mysqld_t -k rename # do not trigger the Audit rule if the process is under the mysqld_t SELinux domain, and add the rename key to the logs auditctl -a exit,always -F dir=/home/ -F uid=0\ # recursively audit every file system access by the root user under the /home directory to files or directories not owned by the original user that is now working as root -C auid!=obj_uid auditctl -e 2 # set the currently loaded rules to be immutable, the rules cannot be changed again until the system is rebooted, must be last rule ``` ```bash # PREPACKAGED AUDIT RULE SETS: # note that watchers (-w) do not cross filesystem boundaries ls /usr/share/doc/audit-*/rules/ cp -v /usr/share/doc/audit-*/rules/30-stig.rules /etc/audit/rules.d/ augenrules --load # FULL TERMINAL KEYSTROKE LOGGING: # man pam_tty_audit vi /etc/pam.d/system-auth session required pam_tty_audit.so disable=* enable=demo # enables keystroke logging for the demo user, and disables it for all other users vi /etc/pam.d/password-auth session required pam_tty_audit.so disable=* enable=demo # enables keystroke logging for the demo user, and disables it for all other users aureport --tty # convert the data logged in the Audit system to a more readable format ``` ```bash # HOW TO EXCLUDE SPECIFIC USERS, GROUPS, OR SERVICES IN AUDITD? # 1. When watching files: -w /opt/application -p wa # audits all writes & attribute-changes to /opt/application and everything beneath it -a always,exit -F dir=/opt/application -F perm=wa # same, converted to the more expressive format, conditions can now be added: -F uid!=USER, -F uid>=1000, -F success=1 (USER, or system users, or unsuccesfull event will prevent triggering the rule) -a always,exit -F dir=/opt/application -F perm=w -F uid!=bob -F uid!=alice -F auid!=root -F uid>=1000 -F gid!=admins -F success=1 # effectively audit all successful writes to /opt/application, except those executed by processes which are owned by bob & alice, user who originally logged in as root, user with a UID less than 1000, process where the primary group is "admins" # 2. When watching syscalls: -a always,exit -F arch=b64 -S clock_settime -F subj_type!=ntpd_t -F auid!=timekeeper # whitelists the use of clock_settime() by any processes running under the ntpd_t SELinux domain and by any processes owned by a user (probably root) who originally logged in as the "timekeeper" user # 3. Do not audit cron, with help of SELinux -a never,user -F subj_type=crond_t -a exit,never -F subj_type=crond_t ``` ## 7. Monitoring File System Changes ```bash yum install aide # CONFIGURATION LINES: # man aide.conf database # location where it reads db when running checks database_out # location where it writes db when it is updated gzip_dbout # new compressed (gzip) db when set to yes # Group definitions: PERMS = p+u+g+acl+selinux+xattrs # group named PERMS monitors permissions, user, group, acl, selinux, extended attributes CONTENT_EX = sha256+ftype+p+u+g+n+acl+selinux+xattrs # content, filetype, access etc. # SELECTION LINES: /etc PERMS # regular, regular expression recursively (don't put trailing "/" at the end) =/testidr PERMS # equals, regular expression non-recursively !/etc/mtab # negative, regular expression of what files or directories not to monitor # MACRO LINES: @@define DBDIR /var/lib/aide # variable definition database=file:@@{DBDIR}/aide.db.gz # variable expansion, sets the database parameter to the value file:/var/lib/aide/aide.db.gz ``` ```bash # CONFIGURING AIDE AND AUDIT: # it is a good idea to configure both aide --init # initializing the aide database aide --check # manually verifying integrity with aide vi /etc/cron.d/aide # in production, you should periodically run AIDE checks 00 17 * * * root /usr/sbin/aide --check aide --update # update the db when EXPECTED changes occur mv -v /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz # do not forget to replace the old database file with the updated file # INVESTIGATING FILE SYSTEM CHANGES: ausearch -i -f /etc/group # select events relevant to the file that you are investigating ausearch -i -f /etc/group -ts "08/07/2018" "09:00:00" # search for events since e.g. date and time of the last AIDE report CWD # current working directory PATH # path to a file involved in the event PROCTITLE # complete command line that triggered the event SYSCALL # system call made to the kernel that trigerred the event a0 # first argument of the system call a1 # second argument of the system call (e.g. O_WRONLY,O_RDWR,O_RDONLY...) auid # a.k.a. audit ID # user ID that was used to log in to the system initially (even when su) euid # a.k.a. effective ID # user ID that the process has for permission checks egid # a.k.a. effective GID # group ID that the process has for permission checks success # yes or no uid # a.k.a. real UID # user ID that started the process (overwritten by su, setuid, setgid) ``` ## 8. Mitigating Risk with SELinux ```bash # MANUAL PAGES: yum install selinux-policy-doc policycoreutils-devel sepolicy manpage -d httpd_t # build the manual page for a specific domain, man /tmp/httpd_selinux.8 sepolicy manpage -a -p /usr/share/man/man8 # by default the sepolicy manpage command generates the manual pages in /tmp # PERSISTENTLY SET THE SELINUX MODE: vi /etc/selinux/config SELINUX=enforcing # check the mode with getenforce # SELINUX REFRESHER: # syntax: user:role:type(domain):level (e.g. system_u:system_r:httpd_t:s0) # PROCESS: ps -Z -C httpd # every process # DIRECTORY/FILE: ls -Z -d /var/www/html # ...directory, file # PORT: semanage port -l | grep "80," # ...and port has a particular security label called the SELinux context semanage port -a -t mysqld_port_t -p tcp 13306 # FILE CONTEXT: semanage fcontext -l # list default file context rules semanage fcontext -a -t httpd_sys_content_t '/virtual(/.*)?' restorecon -Rv /var/www/html/ # although newly created file inherits the context of its parent directory # BOOLEAN: getsebool -a # display all SELinux booleans getsebool httpd_enable_homedirs # default is 'off' setsebool -P httpd_enable_homedirs on # permanently turn the previous boolean to 'on' ``` ```bash # ENABLING SELINUX FROM DISABLED MODE: touch /.autorelabel ; systemctl reboot # start with 'permissive' mode first grep denied /var/log/audit/audit.log # extract the SELinux denials from the log file ausearch -m AVC -ts boot # only display messages from SELinux, and since the last system boot; use restorecon to fix all issues & switch to 'enforcing' mode semanage permissive -a httpd_t # set a specific domain in permissive mode semanage permissive -l # list the domains in permissive mode semanage permissive -d httpd_t # switch a domain back to enforcing ``` ```bash # DEFINING SELINUX USERS: # sysadm_u allows to use 'su', 'sudo'; staff_u can use 'sudo' but not 'su'; user_u cannot use 'su' or 'sudo' semanage user -l # list the SELinux users and their SELinux roles semanage login -l # displays the table that SELinux uses for mapping Linux users to SELinux users id -Z # logged in Linux users can retrieve their associated SELinux user semanage login -a -s sysadm_u operator1 # map existing Linux user 'operator1' to SELinux user 'sysadm_u' semanage login -d -s sysadm_u operator1 # remove the previous mapping semanage login -m -s user_u -r s0 __default__ # modify the default mapping of SELinux user 'user_u' to '__default__' login name - confines all your Linux users to an SELinux user with minimal privileges by default, SELinux range for SELinux user defaults to s0 useradd -Z staff_u developer1 # map a new Linux user operator1 at creation time useradd -G wheel -Z sysadm_u operator2 # map a new Linux user operator2 to SELinux user sysadm_u and add him to Linux group wheel to benefit from existing sudo rule userdel -Z operator2 # remove the mapping at the same time you delete the user # COMMON SELINUX USER BOOLEANS: ssh_sysadm_login # off=users mapped to sysadm_u cannot use SSH to log in user_exec_content # off=prevent users in user_u from executing programs in their home directories and /tmp sysadm_exec_content # staff_exec_content # off=prevent the staff_u SELinux users from executing programs in their home directories and /tmp # SUDO RULES FOR SELINUX: vi /etc/sudoers.d/developers developer ALL= ROLE=sysadm_r /bin/systemctl restart httpd # configure sudo to perform the SELinux role change before running the command ``` ```bash # Three policies: targeted, MLS (Multi-Level Security), minimum yum install setools-console seinfo # list all the objects in the policy seinfo --type # list all the types seinfo --attribute # list all attributes seinfo --attribute=exec_type -x # list the types in an exec_type attribute sesearch -A # list all the rules sesearch -A -s httpd_t -t httpd_config_t -c file # only display rule that allows the httpd_t source type to access files with the httpd_config_t target type seinfo -c # list all classes of the target objects sesearch -A -s httpd_t -t httpd_sys_script_exec_t \ -c file -p execute -C # identify boolean that enables(E)/disables(D) specific rule # DISABLING AND ENABLING "DONTAUDIT" RULES: semodule -DB # disable the dontaudit rules to record all SELinux denials in the log semodule -B # re-enable the dontaudit rules sesearch -D -s postfix_master_t -d # list the dontaudit rules, searches direct rules direct with source of postfix_master_t # CREATING CUSTOM POLICY MODULES: # before using audit2allow, and to collect all the denials in one operation, put SELinux in permissive mode audit2allow -a # generate a policy module for you by analyzing the denials in the audit.log file, print the rules to allow the access audit2allow -a -M mymodule # generate a new SELinux policy module, add the -M modulename option to the previous command semodule -i mymodule.pp # persistently load the new module in SELinux # ANALYZING DOMAIN TRANSITIONS: pstree -Z 1446 # new processes inherit the context type of their parent pstree -Z | grep -e ^systemd -e httpd # when systemd (domain init_t) starts httpd, httpd transitions to the httpd_t domain sesearch -T -s init_t -t httpd_exec_t # list the transition rules with source of init_t and target httpd_exec_t yum install policycoreutils-devel # provides sepolicy transition sepolicy transition -s httpd_t -t unconfined_t # lists all the paths of sequential transitions that can get from the httpd_t domain to the unconfined_t domain # ANALYZING FILE TRANSITIONS: matchpathcon /var/www/html/myimage.png # get the expected context of an object sesearch -T -s crond_t -t var_log_t -c file # list the file transition rules (crond_t -> var_log_t) ``` ## 9. Managing Compliance with OpenSCAP ```bash # THE SCAP SECURITY GUIDE: yum install scap-security-guide # it install openscap-scanner as well (scap command) ls -l /usr/share/xml/scap/ssg/content/ # predefined profiles oscap info /usr/share/xml/scap/ssg/content/ssg-firefox-ds.xml # inspect the security content (parse XCCDF XML and display profiles + ids) oscap xccdf generate guide --profile xccdf_org.ssgproject.content_profile_stig-firefox-upstream \ /usr/share/xml/scap/ssg/content/ssg-firefox-ds.xml > guide.html # generate the HTML security guide for the Upstream Firefox STIG profile # SCAP WORKBENCH: yum install scap-workbench # GUI tool, it also installs scap-security-guide # LOCAL SYSTEM OPENSCAP SCAN: yum install scap-security-guide man scap-security-guide # same as "grep ' results.html # generate a complete report in HTML format from XML (or use --report while running eval) # CUSTOMIZE A SCAP SECURITY GUIDE PROFILE: # create a Tailoring File in scap-workbench first, define custom profile identifier in the process oscap xccdf eval --profile custom_profile_ID --tailoring-file tailoring_file.xml \ --results results.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml # GENERATE A REMEDIATION ANSIBLE PLAYBOOK: # it only includes the tasks to remediate the failed checks oscap xccdf generate fix --profile xccdf_org.ssgproject.content_profile_pci-dss \ --fix-type ansible /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml > pci-dss.yml # remediation from profile oscap xccdf generate fix --profile xccdf_org.ssgproject.content_profile_pci-dss \ --fix-type ansible --result-id "" /root/results.xml > remediation-playbook.yml # remediation from results oscap xccdf generate fix --profile xccdf_com.example_profile --tailoring-file \ lab-tailor.xml --fix-type ansible --result-id "" lab-results.xml --output fix.yml # Ansible remediation with tailoring file. We have to specify the empty result-id, because oscap supports generation of fixes from a result file, that can have results from multiple scans. # APPLYING PROFILES DURING INSTALLATION: # Kickstart file %addon org_fedora_oscap content-type = scap-security-guide profile = pci-dss %end ``` ## 10. Automating Compliance with Red Hat Satellite ```bash # UPLOADING OPENSCAP CONTENT TO THE SATELLITE SERVER: yum install scap-security-guide # ensure the package is installed on the Satellite server foreman-rake foreman_openscap:bulk_upload:default # upload the default OpenSCAP content to your Satellite server, run this on the Satellite server hammer scap-content list # list the SCAP contents in Satellite server (*-ds.xml files, or in the Satellite console - SCAP Contents) # PREPARING SATELLITE CLIENTS FOR OPENSCAP SCANS: # "puppet-foreman_scap_client" package provides the Puppet modules required to set up clients to perform compliance scans # add the "foreman_scap_client" Puppet class listed under the "foreman_scap_client" Puppet module # INITIATING A PUPPET AGENT RUN ON A HOST: # The 'foreman_scap_client' Puppet module installs the 'rubygem-foreman_scap_client' package and its dependencies # Puppet module also configures the '/etc/foreman_scap_client/config.yaml' file on the host with parameters that are needed to run scans and upload results to the Satellite Server # The 'bootstrap.py' script provided by the Satellite Server is used to register a system as both a host and a content host wget https://satellite.lab.example.com/pub/bootstrap.py --no-check-certificate chmod a+x bootstrap.py ./bootstrap.py -l admin -s satellite.lab.example.com -o 'org-example' -L 'Default Location' -a serverkey -g org-hostgroup1 --force vi /etc/foreman_scap_client/config.yaml # contains policy information to be applied on the host :server: 'satellite.lab.example.com' :port: 9090 1: :profile: 'xccdf_org.ssgproject.content_profile_common' rpm -qa | grep -E 'foreman_scap|openscap' vi /etc/cron.d/foreman_scap_client_cron puppet agent --test --verbose # Puppet agent ensures that the compliance policy is correctly configured on the host. You can manually fetch the latest compliance policy this way, or wair for another run # RUNNING AN OPENSCAP SCAN ON A CLIENT: # assumes the Puppet is configured with the above module foreman_scap_client 1 # scan, archives the scan results, and uploads the results to the Satellite Server ``` ### EXECUTING A COMPLIANCE SCAN USING A CUSTOMIZED COMPLIANCE POLICY (TAILORING FILE) IN SATELLITE: - Upload a tailoring file to Satellite: 'Hosts' -> 'Tailoring Files' - Assigning a tailoring file to a compliance policy: 'Hosts' -> 'Policies' This will add ':tailoring_path:' and ':tailoring_download_path:' to the /etc/foreman_scap_client/config.yaml - 'Hosts' -> 'All hosts' -> [Select] -> 'Select Action' -> 'Assign Compliance Policy' - 'Hosts' -> 'All hosts' -> [Select] -> 'Select Action' -> 'Schedule Remote Job' -> 'OpenSCAP' ## 11. Analyzing and Remediating Issues with Red Hat Insights --- _Note: To generate beautiful PDF file, install `latex` and `pandoc`:_ `sudo yum install pandoc pandoc-citeproc texlive` _And then use `pandoc` v`1.12.3.1` to output Github Markdown to the PDF:_ `pandoc -f markdown_github -t latex -V geometry:margin=0.3in -o RH415.pdf R415.md` _For better result (pandoc text-wrap code blocks), you may want to try my [listings-setup.tex](https://gist.github.com/luckylittle/32a90c2024c4183bf01ebc752cbaae51#file-listings-setup-tex):_ `pandoc -f markdown_github --listings -H listings-setup.tex -V geometry:margin=0.3in -o RH415.pdf RH415.md`