Bài tập an toàn thông tin thực chiến trên Linux

# grep ^ENCRYPT_METHOD /etc/login.defs
ENCRYPT_METHOD SHA256

# useradd hieukhin

# grep ^hieukhin /etc/passwd
hieukhin:x:1003:1003::/home/hieukhin:/bin/bash

# grep ^hieukhin /etc/shadow
hieukhin:!!:20232:0:99999:7:::

# passwd hieukhin
Changing password for user hieukhin.
New password:
BAD PASSWORD: The password is a palindrome
Retype new password:
passwd: all authentication tokens updated successfully.

# grep ^hieukhin /etc/shadow
hieukhin:$6$At6tHSJn8AG9CVtx$6bm087IMWskySeS7C39JzD6UxYunrg4JnsQRtGUZ5Aw3/xcWEWLNFus5htSa.UrDYH2zgp0W1mi9bBf7usPIs1:20232:0:99999:7:::

# cat /etc/login.defs
#
# Please note that the parameters in this configuration file control the
# behavior of the tools from the shadow-utils component. None of these
# tools uses the PAM mechanism, and the utilities that use PAM (such as the
# passwd command) should therefore be configured elsewhere. Refer to
# /etc/pam.d/system-auth for more information.
#

#
# Delay in seconds before being allowed another attempt after a login failure
# Note: When PAM is used, some modules may enforce a minimum delay (e.g.
#       pam_unix(8) enforces a 2s delay)
#
#FAIL_DELAY             3

# Currently FAILLOG_ENAB is not supported

#
# Enable display of unknown usernames when login(1) failures are recorded.
#
#LOG_UNKFAIL_ENAB       no

# Currently LOG_OK_LOGINS is not supported

# Currently LASTLOG_ENAB is not supported

#
# Limit the highest user ID number for which the lastlog entries should
# be updated.
#
# No LASTLOG_UID_MAX means that there is no user ID limit for writing
# lastlog entries.
#
#LASTLOG_UID_MAX

# Currently MAIL_CHECK_ENAB is not supported

# Currently OBSCURE_CHECKS_ENAB is not supported

# Currently PORTTIME_CHECKS_ENAB is not supported

# Currently QUOTAS_ENAB is not supported

# Currently SYSLOG_SU_ENAB is not supported

#
# Enable "syslog" logging of newgrp(1) and sg(1) activity.
#
#SYSLOG_SG_ENAB         yes

# Currently CONSOLE is not supported

# Currently SULOG_FILE is not supported

# Currently MOTD_FILE is not supported

# Currently ISSUE_FILE is not supported

# Currently TTYTYPE_FILE is not supported

# Currently FTMP_FILE is not supported

# Currently NOLOGINS_FILE is not supported

# Currently SU_NAME is not supported

# *REQUIRED*
#   Directory where mailboxes reside, _or_ name of file, relative to the
#   home directory.  If you _do_ define both, MAIL_DIR takes precedence.
#
MAIL_DIR        /var/spool/mail
#MAIL_FILE      .mail

#
# If defined, file which inhibits all the usual chatter during the login
# sequence.  If a full pathname, then hushed mode will be enabled if the
# user's name or shell are found in the file.  If not a full pathname, then
# hushed mode will be enabled if the file exists in the user's home directory.
#
#HUSHLOGIN_FILE .hushlogin
#HUSHLOGIN_FILE /etc/hushlogins

# Currently ENV_TZ is not supported

# Currently ENV_HZ is not supported

#
# The default PATH settings, for superuser and normal users.
#
# (they are minimal, add the rest in the shell startup files)
#ENV_SUPATH     PATH=/sbin:/bin:/usr/sbin:/usr/bin
#ENV_PATH       PATH=/bin:/usr/bin

#
# Terminal permissions
#
#       TTYGROUP        Login tty will be assigned this group ownership.
#       TTYPERM         Login tty will be set to this permission.
#
# If you have a write(1) program which is "setgid" to a special group
# which owns the terminals, define TTYGROUP as the number of such group
# and TTYPERM as 0620.  Otherwise leave TTYGROUP commented out and
# set TTYPERM to either 622 or 600.
#
#TTYGROUP       tty
#TTYPERM                0600

# Currently ERASECHAR, KILLCHAR and ULIMIT are not supported

# Default initial "umask" value used by login(1) on non-PAM enabled systems.
# Default "umask" value for pam_umask(8) on PAM enabled systems.
# UMASK is also used by useradd(8) and newusers(8) to set the mode for new
# home directories if HOME_MODE is not set.
# 022 is the default value, but 027, or even 077, could be considered
# for increased privacy. There is no One True Answer here: each sysadmin
# must make up their mind.
UMASK           022

# HOME_MODE is used by useradd(8) and newusers(8) to set the mode for new
# home directories.
# If HOME_MODE is not set, the value of UMASK is used to create the mode.
HOME_MODE       0700

# Password aging controls:
#
#       PASS_MAX_DAYS   Maximum number of days a password may be used.
#       PASS_MIN_DAYS   Minimum number of days allowed between password changes.
#       PASS_MIN_LEN    Minimum acceptable password length.
#       PASS_WARN_AGE   Number of days warning given before a password expires.
#
PASS_MAX_DAYS   99999
PASS_MIN_DAYS   0
PASS_WARN_AGE   7

# Currently PASS_MIN_LEN is not supported

# Currently SU_WHEEL_ONLY is not supported

# Currently CRACKLIB_DICTPATH is not supported

#
# Min/max values for automatic uid selection in useradd(8)
#
UID_MIN                  1000
UID_MAX                 60000
# System accounts
SYS_UID_MIN               201
SYS_UID_MAX               999
# Extra per user uids
SUB_UID_MIN                100000
SUB_UID_MAX             600100000
SUB_UID_COUNT               65536

#
# Min/max values for automatic gid selection in groupadd(8)
#
GID_MIN                  1000
GID_MAX                 60000
# System accounts
SYS_GID_MIN               201
SYS_GID_MAX               999
# Extra per user group ids
SUB_GID_MIN                100000
SUB_GID_MAX             600100000
SUB_GID_COUNT               65536

#
# Max number of login(1) retries if password is bad
#
#LOGIN_RETRIES          3

#
# Max time in seconds for login(1)
#
#LOGIN_TIMEOUT          60

# Currently PASS_CHANGE_TRIES is not supported

# Currently PASS_ALWAYS_WARN is not supported

# Currently PASS_MAX_LEN is not supported

# Currently CHFN_AUTH is not supported

#
# Which fields may be changed by regular users using chfn(1) - use
# any combination of letters "frwh" (full name, room number, work
# phone, home phone).  If not defined, no changes are allowed.
# For backward compatibility, "yes" = "rwh" and "no" = "frwh".
#
#CHFN_RESTRICT          rwh

# Currently LOGIN_STRING is not supported

# Currently MD5_CRYPT_ENAB is not supported

#
# If set to MD5, MD5-based algorithm will be used for encrypting password
# If set to SHA256, SHA256-based algorithm will be used for encrypting password
# If set to SHA512, SHA512-based algorithm will be used for encrypting password
# If set to BLOWFISH, BLOWFISH-based algorithm will be used for encrypting password
# If set to DES, DES-based algorithm will be used for encrypting password (default)
#
ENCRYPT_METHOD SHA256

#
# Only works if ENCRYPT_METHOD is set to SHA256 or SHA512.
#
# Define the number of SHA rounds.
# With a lot of rounds, it is more difficult to brute-force the password.
# However, more CPU resources will be needed to authenticate users if
# this value is increased.
#
# If not specified, the libc will choose the default number of rounds (5000).
# The values must be within the 1000-999999999 range.
#
#SHA_CRYPT_MAX_ROUNDS 5000

# Currently SHA_CRYPT_MIN_ROUNDS is not supported

# Currently BCRYPT_MIN_ROUNDS and BCRYPT_MAX_ROUNDS are not supported

# Currently CONSOLE_GROUPS is not supported

#
# Should login be allowed if we can't cd to the home directory?
# Default is yes.
#
#DEFAULT_HOME   yes

# Currently ENVIRON_FILE is not supported

#
# If defined, this command is run when removing a user.
# It should remove any at/cron/print jobs etc. owned by
# the user to be removed (passed as the first argument).
#
#USERDEL_CMD    /usr/sbin/userdel_local

#
# Enables userdel(8) to remove user groups if no members exist.
#
USERGROUPS_ENAB yes

#
# If set to a non-zero number, the shadow utilities will make sure that
# groups never have more than this number of users on one line.
# This permits to support split groups (groups split into multiple lines,
# with the same group ID, to avoid limitation of the line length in the
# group file).
#
# 0 is the default value and disables this feature.
#
#MAX_MEMBERS_PER_GROUP  0

#
# If useradd(8) should create home directories for users by default (non
# system users only).
# This option is overridden with the -M or -m flags on the useradd(8)
# command-line.
#
CREATE_HOME     yes

#
# Force use shadow, even if shadow passwd & shadow group files are
# missing.
#
#FORCE_SHADOW    yes

#
# Select the HMAC cryptography algorithm.
# Used in pam_timestamp module to calculate the keyed-hash message
# authentication code.
#
# Note: It is recommended to check hmac(3) to see the possible algorithms
# that are available in your system.
#
HMAC_CRYPTO_ALGO SHA512