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CVE-2026-16038 – Payment Bypass (Missing Authorization) – MStore API WordPress Plugin before 4.21.0

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Summary

CVE-2026-16038 is a missing authorization (CWE-862) vulnerability in the MStore API WordPress plugin. The plugin does not verify payments with the payment gateway before marking an order as paid, allowing an unauthenticated attacker to mark an arbitrary order as fully paid without paying. It carries a critical CVSS v3.1 base score of 9.1.

Technical details

  • Root cause: Several payment-completion endpoints do not verify the payment with the payment gateway before marking an order as paid.
  • Trigger conditions: No authentication or user interaction is required to invoke the affected endpoints.
  • Attack vector: Network — reachable remotely against the plugin’s exposed API.
  • Impact: An unauthenticated attacker can mark an arbitrary order as fully paid without paying and obtain goods or services for free, resulting in financial loss to the merchant.

Affected software

  • MStore API WordPress plugin — all versions before 4.21.0.

Severity

  • CVSS v3.1 base score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Update the MStore API plugin to version 4.21.0 or later.
  • If no patch can be applied: Restrict network access to the plugin’s REST API endpoints (for example via a web application firewall or access controls) until the update can be deployed.

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/mstore-api/

References

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Map your entire attack surface (continously)

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4

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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.

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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.

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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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