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 10.4th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Directly requires independent verification of matching output before adverse decisions, mitigating insufficient authenticity checks on data from external sources.
Use of approved PKI certificates provides verifiable data authenticity and origin for communications and artifacts.
Mandates provision of authenticity and integrity artifacts that enable verification of name/address resolution data.
Requires explicit verification of data authenticity from authoritative sources, preventing acceptance of unauthenticated resolution responses.
Control requires verification of data authenticity/integrity (e.g., checksums) after aggregation/packing, directly reducing exploitation of insufficient verification before transmission.
Time synchronization supports reliable freshness verification when checking data authenticity across systems or components.
Mandates verification of data authenticity for software, firmware, and information.
Provenance documentation and monitoring directly enables verification of authenticity for components and data throughout their history.
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.
NVD Description
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).
Deeper analysisAI
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.
Details
- CWE(s)