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CVE-2026-16540 – Unauthenticated Appointment Data Disclosure / Deletion – Simply Schedule Appointmen

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Summary

CVE-2026-16540 is an Incorrect Authorization (CWE-863) vulnerability in the Simply Schedule Appointments WordPress plugin before version 1.6.12.6. The plugin fails to restrict a bulk appointment operation to the requester’s own records, allowing unauthenticated attackers to retrieve the personal data of every appointment on the site and, on premium editions, to permanently delete them. The issue is rated HIGH severity (CVSS 7.5).

Technical details

  • Root cause: A bulk appointment operation exposed via the plugin’s REST endpoint does not properly enforce authorization, so it is not scoped to the requesting user’s own records.
  • Trigger conditions: An attacker sends a request to the affected bulk/purge operation; no authentication or user interaction is required.
  • Attack vector: Network — the vulnerable functionality is reachable over HTTP against an internet-facing WordPress site.
  • Impact: Unauthenticated retrieval of personal data from all appointments across the site (confidentiality breach). On premium editions, the same flaw permits permanent deletion of appointment records.

Affected software

  • Simply Schedule Appointments WordPress plugin — all versions before 1.6.12.6.

Severity

  • CVSS v3.1 base score: 7.5 (HIGH)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Update the Simply Schedule Appointments plugin to version 1.6.12.6 or later.
  • If no patch can be applied yet: Restrict access to the plugin’s REST API routes (wp-json/ssa/v1) at the web server or WAF layer, and consider deactivating the plugin until it can be updated. Review appointment records for signs of unauthorized access or deletion.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw response body: /wp-content/plugins/simply-schedule-appointments/, wp-json/ssa/v1

References

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Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

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Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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