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Linux File System Security > Linux Security > Flashcards

Linux Security Flashcards

1
Q

File Types

A
  • Regular
    d - directory
    l - linksoft link
    c - special or device /dev
    s - socket
    /dev/log - used for communication between processes like syslog
    p - named pipe Allow communication between two local processes
    b - block device/dev
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2
Q

How to change the owner or group on a file/directory

A

chown chgrp -R

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3
Q

Change the permissions on this to rwx for user group and other

A

chmod 777 this
chmod u+rwx,g+rwx,o+rwx this

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4
Q

How do you know a file has an acl on it
setfacl for a user
now a group
now recursively
remove user
remove all entries
If you give a user the w permission can they delete?

A

+ at the end of the permissions

setfacl -m u:delsinm:rwx /home/delinsm/fart.txt

setfacl -m g:delsinm:rwx /home/delsinm/fart.txt

setfacl -rm u:delsinm:rwx /home/delinsm/fart.txt

setfacl -x u:delsinm /home/delsinm/fart.txt

setfacl -b /home/delsinm/fart.txt

No

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5
Q

Change the greeting message for the server

A

vi /etc/motd

or

vi /etc/profile.d/motd.sh
vi /etc/ssh/sshd_config
ReadMotd no
systemctl restart sshd

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6
Q

Orphan Packages

A

Package dependencies of deleted packages

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7
Q

How to find and delete orphaned packages

A

dnf install yum-utils
package-cleanup –leaves
dnf remove ‘package-cleanup –leaves’

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8
Q

difference between update and upgrade

A

upgrade deletes the old packages so if something goes wrong you can’t roll back

update preserves old packages

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9
Q

Show your system version two ways

A

cat /etc/redhat-release
uname -a

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10
Q

delete something that you’ve downloaded via dnf

A

dnf history
dnf history undo 2

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11
Q

update system (this is something you should do for security)

A

dnf update
dnf upgrade

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12
Q

Difference between a service and a package

A

Service is something that runs as a process in your machine

When a service isn’t used it’s just a package

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13
Q

How to disable services through PAM

A

If you see services you don’t use, just change their names and it will disable

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14
Q

Different ways to show services

A

netstat -l (shows listening “ready” packages/services

netstat -tunlp

systemctl -a
systemctl –list-all

chkconfig –list

service –stat-all | grep running

ps -ef (just the running one’s opposed to netstat -l)

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15
Q

Disable a httpd

A

systemctl stop httpd
chkconfig httpd off

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16
Q

Why should you partition different directories like
/boot
/usr
/home
/tmp
/var
/opt

A

This will make it harder for malware to spread
Also, if one fills up completely, like /tmp, it won’t affect the root directory.

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17
Q

What do you used if you want to extend a disk?

A

LVM
Logical Volume Management

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18
Q

What does Ctrl+Alt+Del

A

can log you out and reboot

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19
Q

Check if Ctrl+Alt+Del is enabled
Disable Ctrl+Alt+Del (non-gui)
Disable Ctrl+Alt+Del (with gui)

A

systemctl status ctrl-alt-del.target
systemctl disable ctrl-alt-del.target

older
/etc/init/control-alt-delete.conf
(set parameter as no)

System tools
settings
devices
keyboard
double click logout
press delete and then set

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20
Q

Show all targets
show default target

A

systemctl list-units –type target

systemctl get-default

systemctl set-default whatever

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21
Q

service vs program

A

same thing

22
Q

Should you run multiple services/programs on one server?

A

No, this would make them all vulnerable, they’d also have a lot of ports to try and get into

23
Q

Console

A

port to plug into server to manage it

24
Q

Why would you want to disable usb stick detection?

Disable USB stick detection

A

It could have a script on it to gather data or plant a virus.

touch /etc/modprobe.d/no-usb
install usb-storage /bin/true

25
Q

What are the benefits of chronyd or ntpd? (synchronization)

A

Accurate time info across all devices and applications

Tracking security breaches, network usage or problems. This can be impossible if they’re not on same time.

Financial services and transactions require accurate time keeping which is required by law.

26
Q

Config files for ntp and chrony

checking info on them

where are logs stored

A

/etc/ntp.conf
/etc/chronyd.conf

chronyc sources
ntpq peers

/var/log/messages
/var/log/chrony/

27
Q

Where do you allow/deny users to run crontab?

How to only allow one user to use crontab?

A

add names into either:
/etc/cron.allow
/etc/cron.deny

put root and the other person’s name in allow and nothing in deny

28
Q

What port is rdp?

A

3389

29
Q

Where can you go to look at all ports?

A

/etc/services

30
Q

DAC vs MAC

A

Discretionary Access Control
Up to the admin

Mandatory Access Control
Mandatory

31
Q

After modifying selinux, what should you do?

A

/.autorelabel
Relabel everything for selinux enablement, otherwise it will have to do it on boot which takes forever.

32
Q

What are the different parts of selinux context

A

user:role:type:level

33
Q

How to check http at the socket level

A

netstat -tunlpZ | grep http

34
Q

Turn a boolean on permanently

A

setsebool -P thing on

35
Q

Change the context of a file permanently then just for this session

A

semanage fcontext -at httpd_syscontent_t /absolute/path/filename
or
semanage fcontext -mt httpd_sys_content_t “/absolute/path/directory(/.*)?”

restorecon -Rv /absolute/path/directory

(this will do everything in directory and -m just mean modify instead of -a add)

restorecon -v /absolute/path/filename

chcon -t httpd_syscontent_t filename

36
Q

Troubleshooting context if it’s not showing up, what can you look at?

A

semanage fcontext -l | grep /path/to/filename

cat /etc/selinux/targeted/contexts/files/file_contexts.local

37
Q

Where are actions such as allowing access stored?

A

AVC
Access Vector Cache

38
Q

Command to set and individual domain as permissive

A

semanage permissive -a httpd_t
-a add record
semanage module –list | grep http

39
Q

What format are levels typed out?
Where can you view detailed info on levels?

A

lowlevel-highlevel
c0,c3
/etc/selinux/targeted/setrans.conf

40
Q

Add a user named FART and give hime the staff user option.
Confirm afterword
How would you add FART after he was made to staff?

A

useradd -Z staff_u FART
passwd FART
logout
login
id -Z FART

login as root

semanage login -l

semanage login -d FART

semanage login -d FART (to modify instead of add, use the -m option)

semanage login -as staff_u FART

41
Q

Map __default__ to user_u so you have some SElinux user security going on, This will make default SELinux users user_u

A

semanage login -m -s user_u -r s0 __default__

-m modify
-s seuser
-range

semanage login -l

adduser test
passwd test
login as test
id -Z - to confirm

42
Q

Show further details why selinux denied something

A

sealert -l “*”

43
Q

Say you’re trying to turn the boolean on for httpd_can_network_connect_db and you want it to persist through a reboot. What would that command look like?

A

setsebool -P httpd_can_network_connect_db on

44
Q

Show selinux users and the user what user_u options you have

A

semanage login -l
seinfo -u

45
Q

confirm selinux is running

A

sestatus
getenforce
cat /etc/sysconfig/selinux
cat /etc/selinux/config

46
Q

What can guest_r and xguest_r and user_r and staff_r do?

A

guest_r can execute files in /tmp and /home

xguest_r can access network through browser and execute /tmp and /home

user_r Full permissions but no sudo

staff_r Can run sudo

47
Q

Let sysadmn connect via ssh
add new user called admin and give him sysadmn role and put him in the wheel group

A

setsebool -P ssh_sysadm_login on
adduser -G wheel -Z sysadm_u admin
semanage login -l

48
Q

Chapter 4
Change httpd port to 3131
Change Document root to /var/test_www/html
add file this to it and wget it.

A

Install policycoreutils-python-utils and setroubleshoot-server and httpd

WHEN CHANGING DOCUMENT ROOT YOU NEED TO CHANGE THE TWO DIRECTORY FIELDS AS WELL

semanage port -l | grep http
semanage port -at http_port_t -p tcp 3131

wget localhost:3131/this.txt

sealalert -l “*”

matchpathcon /var/www /var/test_www

semanage fcontext -ae /var/www /var/test_www
restorecon -Rv /var
or
semanage fcontext -at http_sys_content_t “/var/www/test_html(/.*)?”

systemctl restart httpd

49
Q

Install all the selinux packages

A

policycoreutils-python-utils <- Selinux

setroubleshoot-server <- check sealerts

setools-console <- shows seinfo

selinux-policy-devel <- for boolean stuff

50
Q

Let’s say a user can’t access a particular application (via selinux) what can we check to see what might be going wrong?

A

What is the role of the user?
let’s say it’s “user_r”
type in the below command to list what context(type) the user can access
seinfo -ruser_r -x

51
Q

What is a domain in selinux?

A

user, type, role, level,
Levels are determiners for what they can access in terms of other levelers
Sometimes types are just referred to as the domain`

52
Q
A

Linux File System Security (6 decks)

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