The SQL injection vulnerability in the Hide My WP WordPress plugin (versions <= 6.2.3) is possible because of how the IP address is retrieved and used inside a SQL query. The function "hmwp_get_user_ip" tries to retrieve the IP address from multiple headers, including IP address headers that the user can spoof, such as "X-Forwarded-For." As a result, the malicious payload supplied in one of these IP address headers will be directly inserted into the SQL query, making SQL injection possible.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-36916
• https://codecanyon.net/item/hide-my-wp-amazing-security-plugin-for-wordpress/4177158
• https://patchstack.com/database/vulnerability/hide-my-wp/wordpress-hide-my-wp-premium-plugin-6-2-3-sql-injection-sqli-vulnerability
• https://patchstack.com/hide-my-wp-vulnerabilities-fixed/