PwnKit Local Privilege Escalation Vulnerability polkit’s pkexec (CVE-2021-4034)

A memory corruption vulnerability (CVE-2021-4034) in PolKit, a component used in major Linux distributions and some Unix-like operating systems, can be easily exploited by local unprivileged users to gain full root privileges.

https://blog.qualys.com/vulnerabilities-threat-research/2022/01/25/pwnkit-local-privilege-escalation-vulnerability-discovered-in-polkits-pkexec-cve-2021-4034

Patch for Ubuntu is Available

https://ubuntu.com/security/notices/USN-5252-1

If you don’t have any patch please remove suid bit from pxexec tool with this command

chmod 0755 /usr/bin/pkexec

Cloudlinux Setting Global Php Directives

When you want to apply one or more php directives like disable_functions,datetime.zone or something else to all your customers websites,you should write these to /etc/cl.selector/global_php.ini file.After you write your directives enter this command to apply

selectorctl –apply-global-php-ini

/usr/sbin/cagefsctl –setup-cl-selector

You can see the example below.

; This file provides global settings for php.ini of all alt-php packages
; The structure of this file:
; option = value
; To confirm changes (not affecting “date.timezone” and “error_log” options) please run:
; /usr/sbin/cagefsctl –setup-cl-selector
; To confirm changes (including “date.timezone” and “error_log” options) please run:
; /usr/bin/selectorctl –apply-global-php-ini
; or
; /usr/sbin/cagefsctl –apply-global-php-ini
; If you don’t want to change error_log, but want to change date.timezone, you can execute
; selectorctl –apply-global-php-ini date.timezone
; Similarly, command
; selectorctl –apply-global-php-ini error_log
; applies error_log and all other options specified in /etc/cl.selector/global_php.ini file, except date.timezone.
; So, you can specify 0, 1 or 2 parameters from the list: error_log, date.timezone
; using –apply-global-php-ini without arguments applies all global php options including two above
; Example:
; selectorctl –apply-global-php-ini error_log
; selectorctl –apply-global-php-ini date.timezone
; selectorctl –apply-global-php-ini date.timezone error_log
; The latter command has the same effect as /usr/bin/selectorctl –apply-global-php-ini
[Global PHP Settings] disable_functions = mail,system, dl, array_compare, array_user_key_compare, passthru, cat, exec, popen, proc_close, proc_get_status, proc_nice, proc_open,escapeshellcmd,escapeshellarg, show_source,posix_mkfifo, ini_restore, mysql_list_dbs, get_current_user, getmyuid,pconnect, link, symlink, fin, fileread, shell_exec, pcntl_exec, leak, apache_child_terminate,chown, posix_kill, posix_setpgid, posix_setsid, posix_setuid, proc_terminate, syslog, fpassthru, execute, shell, chgrp, passthru, socket_select,socket_create, socket_create_listen, socket_create_pair, socket_listen, socket_accept, socket_bind, socket_strerror, pcntl_fork, pcntl_signal, pcntl_waitpid,pcntl_wexitstatus, pcntl_wifexited, pcntl_wifsignaled, pcntl_wifstopped, pcntl_wstopsig, pcntl_wtermsig, openlog, apache_get_modules, apache_get_version,apache_getenv, apache_note, apache_setenv, virtual, eval, allow_url_fopen, pconnect, p_connect,posix_getpwuid,fileowner,symlink,readlink,stream_select,pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority

Detect new hard disk without reboot

To refresh all devices,Please type the command below as a root user

echo “- – -” | tee /sys/class/scsi_host/host*/scan

Extending / resizing lvm disk to free space

When you use lvm and still have free space on a virtual or physical disk,you can extend your lvm partition to use all free space.

Firstly you should be sure it exists.

Type “vgdisplay” command in root shell.You should see some free space in “Free  PE Size”

After that you should type this command “lvextend -l +100%FREE /dev/volgroup/logvol

After it finishes type resize command according to your file system.

For XFS : xfs_growfs /dev/centos/logvol

For EXT4: resize2fs /dev/centos/logvol

Attention : “logvol” word represents your logical volume.You can see its name in vgdisplay command output.

Install and activate quota on Linux

Install the quota tools on your server.(debian – ubuntu)

sudo apt install quota

Edit your fstab file under etc folder:

/dev/sda1 / ext4 usrquota,grpquota 0 0

and remount it to take effect immediately:

sudo mount -o remount / (or whereever you want to enable)

Enable quota.This command will create two files on file system like /aquota.user and /aquota.group :

sudo quotacheck -ugm /

Activate the quota

sudo quotaon -v /

 

 

 

Mount remote ftp to your server

If you use debian or ubuntu,you should install the package first.

apt-get install curlftpfs

After the installation,create a folder where will you mount to.for example /mnt/rftp

sudo mkdir /mnt/rftp

curlftp’s format and its parameters are simple.for example,we have an ftp account like olriss and password: 123x4P at 192.168.1.199

in local server,mount remote ftp with using this command

curlftpfs olriss:123x4P@192.168.1.199 /mnt/rftp/

curlftps is similar to nfs tools so you can review the mounted ftp area in your mounted drive list.so check it with “mount -a” command.

after your work is finished,you can unmount it with similar way as nfs unmounting.You won’t need all parameters to unmount,You just unmount the folder like below,

umount /mnt/rftp

 

Extending lvm disk by adding space

On Vmware Esx server,You can increase size of your virtual hard disk easily.If you use lvm for your guest os,you will need to add new virtual hard disk or just increase the size of your current disk.This guide will help you to extend size of the disk after you resize of your virtual disk by using vsphere

After increased the size on ESX ,In Linux Terminal;

rescanning the device.host id can change and it depents to your system.you must do that if you dont want to restart your guest;

echo “- – -” > /sys/class/scsi_host/host0/scan

see your disk and partitions;
fdisk -l

lets add new partitions.after you create the partition,you will need to set type of disk to 8e (LVM)
cfdisk /dev/sda (please note your new partition name sample :sda3

see your disk&partitions status again;
fdisk -l

check for available space;
df -h

scan for new partition
partprobe

create physical volume by using new partitions.(disk name may differ.)
pvcreate /dev/sda3

see your volume group and check and confirm
vgdisplay

extend your volume group
vgextend centos /dev/sda3

recheck;
pvscan

extend your logical volume with using the new part
lvextend /dev/centos/root /dev/sda3

in this point,last step may change according to your file system.if you use xfs ;
xfs_growfs /dev/centos/root

for ext4

resize2fs /dev/centos/root

finally see your new available space

df -h

Failed to load SELinux policy. Freezing. Centos 7

If the Linux server fails on boot with a message like this,You should add a parameter in grub boot editor which appears on boot.

When your server opens kernel list will appear on your screen.You use the arrow keys a kernel line like “Centos Linux 7 (Core) with Linux….” and type “e” button to edit.

After that,find the line which starts with linux add “selinux=0” like this below and type Ctrl button+x.Your server will open normally.After your server boots,fix the main problem about selinux that you have previously changed

Cloudlinux saving common php settings permanently for all installed versions

When you update cloudlinux,it also will be updated the php.ini files.Therefore you will lost your customized php settings like disable_functions.You can write some of yours into common settings file instead of editing php.ini’s directly.

Login to your cloudlinux and change directory to /etc/cl.selector/

You will see the file named global_php.ini.It is effective for your all installed alt-php* versions.Please open it by your favorite editor like nano or vi.

Sample global_php.ini with applied disable_functions directive

; This file provides global settings for php.ini of all alt-php packages
; The structure of this file:
; option = value
; To confirm changes (not affecting “date.timezone” and “error_log” options) please run:
; /usr/sbin/cagefsctl –setup-cl-selector
; To confirm changes (including “date.timezone” and “error_log” options) please run:
; /usr/bin/selectorctl –apply-global-php-ini
; or
; /usr/sbin/cagefsctl –apply-global-php-ini
; If you don’t want to change error_log, but want to change date.timezone, you can execute
; selectorctl –apply-global-php-ini date.timezone
; Similarly, command
; selectorctl –apply-global-php-ini error_log
; applies error_log and all other options specified in /etc/cl.selector/global_php.ini file, except date.timezone.
; So, you can specify 0, 1 or 2 parameters from the list: error_log, date.timezone
; using –apply-global-php-ini without arguments applies all global php options including two above
; Example:
; selectorctl –apply-global-php-ini error_log
; selectorctl –apply-global-php-ini date.timezone
; selectorctl –apply-global-php-ini date.timezone error_log
; The latter command has the same effect as /usr/bin/selectorctl –apply-global-php-ini
[Global PHP Settings] disable_functions= proc_open,escapeshellcmd,escapeshellarg, show_source,
posix_mkfifo, ini_restore, mysql_list_dbs, get_current_user, getmyuid,pconnect, link, symlink, fin, exec, fileread, shell_exec, pcntl_exec, leak, apache_child_terminate, ch
own, posix_kill, posix_setpgid, posix_setsid, posix_setuid, proc_terminate, syslog, fpassthru, execute, shell, chgrp, stream_select, passthru, socket_select, socket_create,
socket_create_listen, socket_create_pair, socket_listen, socket_accept, socket_bind, socket_strerror, pcntl_fork, pcntl_signal, pcntl_waitpid, pcntl_wexitstatus, pcntl_wif
exited, pcntl_wifsignaled, pcntl_wifstopped, pcntl_wstopsig, pcntl_wtermsig, openlog, apache_get_modules, apache_get_version, apache_getenv, apache_note, apache_setenv, vir
tual, eval, allow_url_fopen, pconnect, p_connect,posix_getpwuid,fileowner,sym

You should write your own directives down the global php settins tag in same syntax of standart php.ini [Global PHP Settings]

After then save and close the editor and apply it by this command

[root@srv ~]# selectorctl –apply-global-php-ini