Formidable Form Builder <= 4.09.04 - Unauthenticated Stored Cross-Site Scripting
Strategic Overview
- Status
- Patched in 4.09.05
- Affected Plugin
- Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
- Affected Version
< 4.09.05- CVSS
- 9.6Critical
- Weakness type
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
- CVE
CVE-2021-24884
At a glance
CVE-2021-24884 is a critical-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Formidable Forms WordPress plugin, affecting versions < 4.09.05. It carries a CVSS score of 9.6 (reachable over the network; low attack complexity; high confidentiality, integrity, availability impact). Exploitation requires no authentication. The issue is fixed in version 4.09.05; sites on affected versions should update now. Disclosed January 2021, reported by Maximilian Barz.
Vulnerability Overview
The Formidable Form Builder WordPress plugin before 4.09.05 allows to inject certain HTML Tags like <audio>,<video>,<img>,<a> and<button>.This could allow an unauthenticated, remote attacker to exploit a HTML-injection byinjecting a malicous link. The HTML-injection may trick authenticated users to follow the link. If the Link gets clicked, Javascript code can be executed. The vulnerability is due to insufficient sanitization of the "data-frmverify" tag for links in the web-based entry inspection page of affected systems. A successful exploitation incomibantion with CSRF could allow the attacker to perform arbitrary actions on an affected system with the privileges of the user. These actions include stealing the users account by changing their password or allowing attackers to submit their own code through an authenticated user resulting in Remote Code Execution. If an authenticated user who is able to edit Wordpress PHP Code in any kind, clicks the malicious link, PHP code can be edited.
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. A successful exploit has high impact on confidentiality, integrity, availability — full site compromise territory.
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Formidable Forms < 4.09.05 carries this weakness at data-frmverify, and reaching it takes no account at all. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.
Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For Formidable Forms the fix is 4.09.05: builds < 4.09.05 are affected, anything from 4.09.05 onward is not.
Remediation
Update to version 4.09.05, or a newer patched version
How does WordSec protect against this?
Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Formidable Forms 4.09.05 closes this, and updating the plugin is the step that ends it.
- Firewall
- Login Security
- Alerts
External References
Related records
Same weakness class
Other vulnerabilities in Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
- 9.8CVE-2023-1405: Formidable Forms <= 6.1.2 PHP Object Injection
CVE-2023-1405 - 9.8CVE-2019-15780: Formidable Form Builder <= 4.02 PHP Object Injection
CVE-2019-15780 - 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
- 7.5CVE-2026-2890: Formidable… Unauthenticated Payment Integrity Bypass
CVE-2026-2890 - 7.1CVE-2023-24419: Formidable Form Builder <= 5.5.6 CSRF
CVE-2023-24419 - 6.5CVE-2023-2877: Formidable Forms Arbitrary Plugin Installation
CVE-2023-2877
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