# Calculated Fields Form <= 5.5.2.6 - Unauthenticated Payment Amount Manipulation via 'cff_sum_values' Price Check Bypass

- **ID:** WPSEC-2026-2570
- **Plugin:** Calculated Fields Form – AI Form Builder for WordPress – Contact, Payment, Quote, Quiz & More (`calculated-fields-form`), https://wordpress.org/plugins/calculated-fields-form/
- **Affected versions:** from 5.5.2.4 before 5.5.2.7
- **Fixed in:** 5.5.2.7 (Update to 5.5.2.7 or later.)
- **Severity:** Low 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **Weakness:** CWE-602
- **Usage among sites WPSec scans:** plugin Low, affected versions None seen (as of 2026-11-05)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/calculated-fields-form
- **Fix released:** 2026-11-04
- **Published:** 2026-11-05
- **URL:** https://wpsec.com/vuln/WPSEC-2026-2570/

## Description

The Calculated Fields Form plugin for WordPress is vulnerable to a server-side price validation bypass via the 'cff_sum_values' parameter in versions 5.5.2.4 up to, and including, 5.5.2.6. The 'Check by sum' request-cost validation compared the submitted price against subtotals taken from a JSON snapshot sent by the browser, so the server never worked out the field values itself. This makes it possible for unauthenticated attackers to submit a public payment form with a forged snapshot and a lowered price, and so pay less than the real price through the configured payment gateway (e.g. Stripe Checkout). This only affects forms where the site owner enabled the price check.

## References

- https://wpsec.com/vuln/WPSEC-2026-2570/
- https://plugins.svn.wordpress.org/calculated-fields-form/tags/5.5.2.7/
- https://wordpress.org/plugins/calculated-fields-form/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-2570/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Free to use, share and adapt, also commercially, if you credit WPSec and link to this advisory.