You are absolutely correct that processing IPs is GDPR-relevant, as they are considered personal data under the regulation. However, GDPR does allow the storage and processing of IPs for security purposes under the legitimate interest basis (Article 6(1)(f)), as long as this processing is necessary and proportional. You can find more details here: https://gdpr.eu/article-6-how-to-process-personal-data-legally/.
Storing IPs is critical for identifying and mitigating security threats, and this applies to nearly all security software, including plugins like Ninja Firewall and cPFence. Of course, it's essential for both the company's and the client website's privacy policy to mention the processing of IPs. This requirement is not specific to cPFence but applies to any security tool or plugin handling personal data.
I understand your concerns, and I've reached out to the legal team of one of my clients, who frequently deals with GDPR compliance, to review this matter further. I'll share any updates or insights they provide. Acting early to address GDPR considerations is always a good practice to avoid surprises later. Thank you once again.