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CVE-2026-39493 – Unauthenticated SQL Injection – Simply Schedule Appointments WordPress Plugin ≤ …

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Summary

CVE-2026-39493 is a critical unauthenticated SQL injection vulnerability in the Simply Schedule Appointments booking plugin for WordPress, developed by NSquared, affecting all versions up to and including 1.6.9.27. The flaw allows any unauthenticated remote attacker to inject arbitrary SQL commands via unsanitised parameters in the plugin’s REST API, enabling extraction of sensitive data from the underlying WordPress database. With a CVSS base score of 9.3 (Critical) and over 60,000 active installations reported on WordPress.org, this vulnerability poses a significant risk to internet-facing WordPress deployments.

Technical details

  • Root cause: Insufficient escaping of user-supplied input and lack of proper SQL query preparation in the plugin’s REST API endpoint handling. Parameters such as append_where_sql and order accepted via REST request bodies are passed into database queries without adequate sanitisation or parameterisation.
  • Trigger conditions: No authentication is required. An attacker can send a crafted HTTP request directly to the plugin’s exposed REST API endpoint (e.g., via the /wp-json/ssa/v1/ route) without holding any account credentials on the target site.
  • Attack vector: Fully remote and network-accessible; no user interaction is required. The attack is low-complexity and can be automated.
  • Impact: Successful exploitation allows unauthenticated attackers to append additional SQL statements to existing queries, extracting sensitive information from the WordPress database — including user credentials, personal data, appointment records, and any other data stored by the site. The CVSS vector reflects a Changed scope (S:C), indicating the potential for data exposure that crosses privilege boundaries. The primary risk is high-confidence data theft (C:H).

Affected software

  • Simply Schedule Appointments (WordPress plugin by NSquared) — all versions up to and including 1.6.9.27

Severity

  • CVSS v3.1 Base Score: 9.3 (Critical)
  • Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:L

Mitigation and recommended actions

  • Immediate: Update the Simply Schedule Appointments plugin to the latest available version. As of the date of this advisory, the current version on WordPress.org is 1.6.12.0. Administrators should prioritise upgrading to the most current release to benefit from all subsequent security improvements.
  • If immediate patching is not feasible:
    • Restrict access to WordPress REST API endpoints at the web server or WAF layer, limiting /wp-json/ssa/v1/ access to trusted IP ranges where operationally possible.
    • Deploy a web application firewall rule to block requests containing SQL injection patterns targeting the plugin’s REST endpoints.
    • Monitor database access logs and WordPress REST API logs for anomalous query patterns.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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