CVE-2026-2428
Published: 27 February 2026
Summary
CVE-2026-2428 is a high-severity Insufficient Verification of Data Authenticity (CWE-345) vulnerability in Fluentforms (inferred from references). Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 10.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 CM-6 (Configuration Settings) and IA-9 (Service Identification and Authentication).
Deeper analysis
CVE-2026-2428 is an Insufficient Verification of Data Authenticity vulnerability (CWE-345) in the Fluent Forms Pro Add On Pack plugin for WordPress, affecting all versions up to and including 6.1.17. The issue arises because PayPal Instant Payment Notification (IPN) verification is disabled by default, with the `disable_ipn_verification` setting defaulting to `'yes'` in `PayPalSettings.php`. This configuration exposes a publicly accessible IPN endpoint to forged notifications without authenticity checks.
Unauthenticated attackers can exploit this vulnerability remotely with low complexity and no privileges, as indicated by its CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N). By sending crafted PayPal IPN messages to the endpoint, attackers can falsely mark unpaid form submissions as "paid," thereby triggering post-payment automations such as sending emails, granting user access, or delivering digital products.
Advisories and patch information are detailed in the Fluent Forms changelog at https://fluentforms.com/docs/changelog/#2-toc-title and Wordfence threat intelligence at https://www.wordfence.com/threat-intel/vulnerabilities/id/e5c62e54-da06-4b44-ba70-63065e664b0d?source=cve, published on 2026-02-27.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8986
Vulnerability details
The Fluent Forms Pro Add On Pack plugin for WordPress is vulnerable to Insufficient Verification of Data Authenticity in all versions up to, and including, 6.1.17. This is due to the PayPal IPN (Instant Payment Notification) verification being disabled by…
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default (`disable_ipn_verification` defaults to `'yes'` in `PayPalSettings.php`). This makes it possible for unauthenticated attackers to send forged PayPal IPN notifications to the publicly accessible IPN endpoint, marking unpaid form submissions as "paid" and triggering post-payment automation (emails, access grants, digital product delivery).
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct exploitation of unauthenticated public IPN endpoint due to missing authenticity verification in a web-facing WordPress plugin.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Requires secure configuration settings for the PayPal IPN verification to be enabled, directly countering the default insecure `disable_ipn_verification` setting that allows forged notifications.
Mandates protective safeguards for publicly accessible machine-to-machine interfaces like the IPN endpoint to prevent unauthorized forged payment notifications.
Enforces identification and authentication of external services such as PayPal for system-to-system connections, ensuring IPN notifications are authentic before processing.