Strategic Overview
- Status
- Patched in 4.02.01
- Affected Plugin
- Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
- Affected Version
< 4.02.01- CVSS
- 9.8Critical
- Weakness type
- CWE-502 · Deserialization of Untrusted Data
- CVE
CVE-2019-15780
At a glance
CVE-2019-15780 is a critical-severity Deserialization of Untrusted Data vulnerability in the Formidable Forms WordPress plugin, affecting versions < 4.02.01. It carries a CVSS score of 9.8 (reachable over the network; low attack complexity; high confidentiality, integrity, availability impact). Exploitation requires no authentication. The issue is fixed in version 4.02.01; sites on affected versions should update now. Disclosed August 2019, reported by Sam Thomas.
Vulnerability Overview
The formidable plugin before 4.02.01 for WordPress has unsafe deserialization.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site, and no interaction from a victim user. A successful exploit has high impact on confidentiality, integrity, availability — full site compromise territory.
CWE-502: Deserialization of Untrusted Data
Reaching this weakness in Formidable Forms < 4.02.01 takes a caller who can reach the endpoint. Deserialization of untrusted data means the application reconstructs objects from input a caller controls, letting the attacker choose which classes get instantiated and what their properties hold.
A workable chain turns deserialization into file writes, deletions or code execution, depending on what the loaded classes do in their magic methods. For Formidable Forms the fix is 4.02.01: builds < 4.02.01 are affected, anything from 4.02.01 onward is not.
Remediation
Update to version 4.02.01, or a newer patched version
How does WordSec protect against this?
The attempt arrives as an ordinary request to Formidable Forms: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Formidable Forms 4.02.01 closes this, and updating the plugin is the step that ends it.
- Firewall
- Scanner
- Alerts
External References
Related records
Other vulnerabilities in Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
- 9.6CVE-2021-24884: Formidable Form Builder <= 4.09.04 Stored XSS
CVE-2021-24884 - 9.1Formidable Form Builder <= 2.0.21 Missing Authorization Checks
- 8.8CVE-2014-9309: Formidable Form Builder <= 1.07.11 SQL Injection
CVE-2014-9309 - 8.6Formidable Form Builder < 2.05.03 SQL Injection
- 8.3CVE-2017-20192: Formidable Form Builder < 2.05.03 Stored XSS
CVE-2017-20192 - 7.5CVE-2026-2890: Formidable… Unauthenticated Payment Integrity Bypass
CVE-2026-2890 - 7.2CVE-2026-18331: Formidable Forms <= 6.33.1 Stored Cross-Site Scripting
CVE-2026-18331 - 7.1CVE-2023-24419: Formidable Form Builder <= 5.5.6 CSRF
CVE-2023-24419
Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C