Urgent: The Events Calendar (≤ 6.15.1) — Unauthenticated SQL Injection (CVE-2025-9807) — What WordPress Site Owners Must Do Now

Published: 11 September 2025
Author: Hong Kong Security Expert

Summary

• Software affected: The Events Calendar (WordPress plugin)
• Vulnerable versions: ≤ 6.15.1
• Fixed in: 6.15.1.1
• CVE: CVE-2025-9807
• Required privilege: Unauthenticated (no login required)
• Severity: High — CVSS 9.3
• Primary risk: Unauthenticated SQL injection leading to database disclosure, modification, or remote code execution when chained with other weaknesses

If your site uses The Events Calendar plugin and the plugin version is 6.15.1 or older, treat this as an emergency. An unauthenticated SQL injection in a widely used plugin allows unauthenticated attackers to interact with your database. Below I explain the vulnerability impact, safe detection methods, practical mitigations, incident-response steps, and practical compensating controls.

NOTE: Do not delay — update the plugin to 6.15.1.1 or later as your primary mitigation. Read on for compensating controls and incident-response guidance.

Table of contents

1. What happened (plain language)
2. Why this is dangerous (impact)
3. High-level technical explanation (what to look for)
4. How attackers may exploit this (risk scenarios)
5. Detecting compromise and indicators of attack
6. Immediate actions for site owners
7. Virtual patching and WAF-based mitigations (managed WAF and virtual patching)
8. Example WAF rule patterns (safe, non-exploit proofing)
9. Incident response and recovery checklist
10. Post-incident hardening and best practices
11. Closing notes

1) What happened (plain language)

A critical SQL injection vulnerability was discovered in The Events Calendar plugin for WordPress that allows unauthenticated visitors to inject SQL into database queries handled by the plugin. Because the flaw requires no authentication, attackers can attempt exploitation by sending specially crafted HTTP requests to endpoints provided by the plugin.

In short, an attacker could read or modify information in your WordPress database (posts, users, meta, event data), create or elevate user privileges, or pivot to achieve remote code execution depending on your environment and other installed software.

2) Why this is dangerous (impact)

• Unauthenticated: No account required to trigger the vulnerability. Remote actors on the internet can target your site.
• Database-level control: Successful SQL injection can leak sensitive data (email addresses, hashed passwords, API keys, event/location details) and permit destructive changes.
• Mass exploitation potential: Widely used plugins with unauthenticated flaws are early targets for automated scanners and botnets; rapid, large-scale compromise is possible.
• Chainability: SQLi can be combined with stored XSS, file-write bugs, or poorly protected admin endpoints to achieve full site takeover.
• Business impact: Data theft, defacement, downtime, regulatory exposure, and reputational damage.

3) High-level technical explanation (what to look for)

Specific implementation details are part of the vendor’s disclosure and patch notes, but the core issue is insufficient input handling in a query constructed by the plugin. Common root causes include:

• Direct concatenation of user-controlled data into SQL statements without parameterized queries or prepared statements.
• Failure to validate input types and allowed characters before including them in SQL statements.
• Server-side endpoints (REST API, admin-ajax, or custom endpoint) that accept parameters and pass them into wpdb->get_results() or similar without sanitisation.

Where to inspect:

• The plugin’s REST endpoints and AJAX handlers.
• Any code paths that build SQL conditions dynamically from GET/POST parameters.
• Changelog or release notes from the plugin author for the exact patched functions.

We do NOT publish proof-of-concept exploit code here — exposing step-by-step exploitable payloads for an actively exploitable, unauthenticated vulnerability would put more sites at risk. If you are performing authorised security testing on your own site, limit tests to non-production copies or schedule maintenance windows.

4) How attackers may exploit this (risk scenarios)

• Automated scanning bots: Inventory sites with The Events Calendar and probe known endpoints, then attempt injection patterns.
• Data exfiltration: Use boolean or error-based SQLi techniques to retrieve sensitive fields such as user emails or hashed passwords.
• Stored payload placement: Inject content into event descriptions or other database fields that then becomes active in the frontend (combined with XSS).
• Privilege escalation: Modify wp_users or usermeta tables to insert or elevate admin accounts.
• Lateral movement: If attackers can influence file writes or trigger functionality that allows writing to the filesystem, they may drop backdoors.

Because this is unauthenticated, the window for automated mass-scanning and subsequent exploitation is measured in hours-to-days following public disclosure. Do not assume your site will be spared.

5) Detecting compromise and indicators of attack

Look for the following signs in your logs and database that may indicate attempted or successful exploitation:

Web server / application logs

• Unusual request spikes to plugin endpoints (URLs under the plugin namespace or REST routes added by the plugin).
• Requests containing SQL keywords in query strings or POST bodies (e.g., SELECT, UNION, –, OR 1=1).
• Requests from high-volume IPs or IPs with repeated probing attempts.

Database and application indicators

• Unexpected changes in wp_posts, wp_postmeta, wp_users, wp_usermeta, or custom plugin tables.
• Strange admin users created recently, especially with weak or blank passwords.
• Event records with unusual content (injected SQL fragments or encoded payloads).
• Errors in logs that reveal SQL syntax errors or stack traces from plugin functions.

Filesystem signs

• New PHP files in wp-content/uploads, wp-content/plugins, or other writable directories.
• Modifications to wp-config.php or theme files (more likely if other write holes exist).

Recommended log searches (examples you can run safely):

• Search your web server access log for requests hitting the plugin’s endpoints.
• Use grep or your logging platform to detect SQL-related tokens in requests: SELECT, UNION, SLEEP(, BENCHMARK(, –, /*, @@, information_schema.
• Inspect DB audit logs (if present) for odd queries at times you did not perform maintenance.

6) Immediate actions for site owners (ordered, practical)

If your site runs The Events Calendar ≤ 6.15.1, follow these immediate steps:

1. Patch first
   • Update The Events Calendar plugin to 6.15.1.1 or later as soon as possible. This is the single most effective measure.
   • If you use automatic updates, verify the plugin was updated successfully and clear caches.
2. If you cannot update immediately, apply compensating controls
   • Use runtime protections such as a Web Application Firewall (WAF) or virtual patching rules that block known exploitation patterns for this vulnerability.
   • Restrict access to plugin endpoints using IP allowlisting where feasible (for example, admin-only calls from office networks).
   • Disable public-facing endpoints of the plugin if you are not using them (some plugins allow turning off REST support).
3. Monitor logs aggressively
   • Watch web server access logs and WAF logs for probing attempts and the indicators listed above.
   • Temporarily increase alerting sensitivity for suspicious requests toward plugin endpoints.
4. Take a backup
   • Create a fresh file + database backup immediately and store it off-site.
   • If you suspect compromise, take a snapshot before making changes for later forensic review.
5. Scan and clean
   • Run malware scans and code integrity checks.
   • If suspicious files are found or DB changes detected, follow an incident response process (see section 9).

7) Virtual patching and WAF-based mitigations (managed WAF and virtual patching)

If you cannot update immediately (for example, due to customisations that require testing), virtual patching via a WAF is a practical compensating control. Below are neutral, practical notes based on incident-response experience.

What virtual patching does

• Blocks malicious requests before they reach the vulnerable code path.
• Applies rules that detect and drop SQL injection payloads targeted at known plugin endpoints.
• Prevents large-scale automated exploitation while you plan and perform a safe update.

Why managed protections can be useful

• Rapid deployment: A well-configured rule can be created and applied in minutes, protecting sites that share the same vulnerability.
• Rule tuning: Rules can be refined to reduce false positives while covering variants attackers attempt.
• Logging and forensics: WAFs provide logs that help identify blocked attempts and the actors behind them.

Note: Virtual patching is a stop-gap, not a replacement for the official plugin update. Prioritise applying the vendor patch as soon as possible.

8) Example WAF rule patterns (safe, non-exploit proofing)

Below are safe, high-level rule patterns and approaches commonly used to reduce exposure to SQLi in plugin endpoints. These are conceptual and must be adapted and tested in your environment to avoid false positives.

• Block unnecessary endpoints: If the plugin exposes API paths you do not use (e.g., /wp-json/tribe/events/v1/*), return 403 for unauthenticated calls or restrict by IP/country.
• Parameter validation and whitelisting: Enforce allowed character classes and length restrictions for parameters (IDs, slugs, page numbers). Reject parameters containing SQL metacharacters where they are not expected.
• Generic SQLi token detection: Detect high-risk tokens in user-supplied parameters and block or challenge:
  • Tokens to watch for: UNION, SELECT, INSERT, DROP, SLEEP(, BENCHMARK(, –, /*, */, information_schema
  • Reject requests that include these tokens in parameters that should never contain them.
• Anomaly scoring and rate limits: Rate-limit requests to plugin endpoints and apply anomaly scoring; block clients that exceed thresholds or show high-risk token use.
• Encoding and content-length checks: Monitor for percent-encoded SQL payloads or large URL-encoded payloads that may indicate obfuscation attempts.

Sample (pseudocode) WAF rule — conceptual only:

IF request.path STARTS_WITH "/wp-json/tribe/events" AND request.auth IS NULL THEN
  IF request.query_params CONTAINS_REGEX "(?i)(union|select|information_schema|benchmark|sleep)\b" THEN
     BLOCK request WITH 403
  ENDIF
  IF request.query_params['id'] NOT MATCH "^\d{1,6}$" THEN
     BLOCK request WITH 403
  ENDIF
ENDIF

Important: Test any rule on staging before deploying to production. Overly broad rules can break legitimate plugin functionality. Work with your host or security partner to tune rules for your site.

9) Incident response and recovery checklist

If you suspect exploitation or find suspicious artifacts, follow this prioritised checklist:

A. Containment

• Apply WAF rules or temporarily disable vulnerable plugin endpoints.
• Consider setting the site to maintenance mode to stop further exposure.

B. Evidence preservation

• Create snapshots of server and database.
• Export logs (web server, application, WAF) for the relevant time window.

C. Analysis

• Review access logs for suspicious requests and timeline.
• Inspect database for unauthorised changes: newly created users, changed capabilities, modified posts/events.
• Scan filesystem for unknown PHP files or recently modified files.

D. Remediation

• Update plugin to patched version (6.15.1.1 or later).
• Remove unauthorised users and reset passwords for administrator accounts.
• Restore files from clean backups if file tampering is confirmed.
• Rotate credentials that may have been exposed: API keys, database passwords, external service tokens.

E. Post-incident hardening

• Re-run malware and rootkit scanners.
• Implement multi-factor authentication for all admin users.
• Strengthen logging and alerting to detect similar activity earlier.

F. Communication

• If personal data was exposed, follow applicable breach notification laws and inform stakeholders and hosting provider.
• Document timeline and actions taken for internal and regulatory purposes.

10) Post-incident hardening and best practices

Use this incident as a prompt to reinforce your overall WordPress security posture:

• Keep plugins and WordPress core updated. Apply updates to staging first if you need to test customisations.
• Reduce plugin footprint: deactivate and remove plugins you do not actively use.
• Apply principle of least privilege: reduce admin users and use role-based access controls.
• Enforce strong passwords and enable multi-factor authentication (MFA) for all privileged accounts.
• Consider a managed WAF or runtime protection for emergency virtual patching when updates must be delayed.
• Schedule regular backups with off-site retention and periodic restore tests.
• Implement file integrity monitoring to detect unauthorized code changes quickly.
• Log and alert on new admin account creation and other high-risk events.

11) Closing notes

As a Hong Kong–based security specialist with incident-response experience across Asia, my advice is direct: this SQL injection vulnerability is serious and time-sensitive because it is exploitable without authentication and affects a widely used plugin. The single best action is to update The Events Calendar to the fixed version immediately.

If you must delay updating, apply runtime protections (WAF, IP restrictions), increase monitoring, and prepare backups and a response plan. If you detect suspicious activity or uncertain changes, preserve evidence and engage a qualified incident-response service or your hosting provider for triage and recovery.

Stay pragmatic: patch early, keep tested backups, and monitor your logs closely during the days following public disclosure.

References & further reading

• Official plugin changelog and vendor advisory (check the plugin page or vendor support for the precise patched files and guidance).
• CVE details: CVE-2025-9807.
• OWASP guidance on SQL Injection and web application testing.

If you perform active testing, always work on a staging copy and obtain proper authorisation for security testing.