How a managed firewall and monitoring can help (neutral guidance)

If you have access to a managed firewall or host-provided request filtering, use it to reduce exposure while you prepare to update. Appropriate controls include:

• Virtual patching: block or sanitise requests that contain script-like patterns in headers (User-Agent, Referer, etc.).
• Request inspection: filter or normalise headers before they reach application code.
• Continuous monitoring: file integrity monitoring and alerts for unusual admin activity or new users.
• Incident response capability: the ability to quarantine a site quickly and run forensics if compromise is suspected.

Step-by-step incident response and recovery plan

1. Containment
   • Enable WAF rules immediately blocking requests with <, >, script, onerror, and onload in header fields.
   • Temporarily restrict access to /wp-admin via IP whitelisting or HTTP auth.
   • Disable the vulnerable plugin if you can do so safely without breaking critical functionality. Evaluate risk vs. functionality.
2. Assessment
   • Create a forensic snapshot (file-level and DB dump) stored off-site for investigation.
   • Scan for unusual files, recently modified files, new user accounts, and strange scheduled tasks.
   • Inspect plugin-specific database tables for malicious payloads stored in user-agent fields or logs.
3. Eradication
   • Remove malicious entries from the database (carefully, with backups).
   • Remove any malicious files or restore clean files from a known good backup.
   • Update the plugin to 3.8.1 or later and update all other plugins/themes/core.
4. Recovery
   • Change all admin passwords and rotate any exposed API keys.
   • Revoke stale sessions and reset security keys (WP salts).
   • Apply recommended hardening: two-factor authentication, least privilege for accounts, remove unused plugins/themes.
   • Monitor logs and run repeated malware scans.
5. Post-Incident
   • Review how the incident occurred, update patching and monitoring processes to prevent recurrence.
   • If you host client sites, notify clients and provide a summary of what happened and what remedial actions were taken.
   • Consider professional forensic investigation if sensitive data or extensive damage is suspected.

Practical remediation checklist (copyable)

• Update Blackhole for Bad Bots to version 3.8.1 or later.
• If update not possible, deploy WAF rule to block suspicious User-Agent header patterns.
• Search and clean DB for stored payloads in plugin log tables.
• Rotate all administrator credentials and revoke sessions.
• Enable 2FA for all administrator accounts.
• Scan site files for backdoors/malware and replace altered files with clean versions.
• Harden admin endpoints (restrict /wp-admin, enable HTTP auth if needed).
• Backup site and keep immutable forensic copies before major cleaning.
• Monitor site for a minimum of 30 days for signs of re-infection.

How to harden WordPress against stored XSS and header-based attacks

• Sanitize and validate input — never trust header values; treat them as untrusted input.
• Output encoding — any stored strings rendered in HTML must be encoded using proper escaping functions (e.g., esc_html, esc_attr in WordPress).
• Least privilege — limit who can view plugin logs and admin pages to the minimum necessary roles.
• Restrict admin access — IP-restrict /wp-admin or protect with HTTP Basic Auth where appropriate.
• Enable two-factor authentication to reduce impact of session theft.
• Security headers and CSP — implement Content Security Policy, X-Content-Type-Options, X-Frame-Options, Referrer-Policy, and Strict-Transport-Security.
• WAF and rate limiting — use request filtering and rate-limits to block obvious attack patterns.
• Monitoring — monitor file changes, admin user creation, and unusual scheduled tasks; keep an audit trail of admin actions.
• Regular updates — keep core, themes, and plugins updated and subscribe to a vulnerability feed.

Sample WAF rule suggestions (conceptual)

These are conceptual and must be adapted to your WAF engine. They’re for immediate mitigation while you patch:

• Block if header User-Agent contains (case-insensitive) or patterns like onerror= or onload=.
• Block if header values contain javascript: or encoded variants (%3Cscript, <).
• Enforce maximum header length for User-Agent (e.g., 512 bytes) — attackers often use long payloads.
• Rate-limit requests from new client IPs targeting admin endpoints and plugin AJAX endpoints.
• Block known scanning/spam IPs and TOR exit nodes with caution to avoid blocking legitimate users.