Skip to content
Fencer Vulns
critical 9.6

CVE-2021-24884 json

Formidable Form Builder < 4.09.05 - Unauthenticated Stored Cross-Site Scripting

published 2021-10-25 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-11796

cvss
9.6
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.1%
EPSS 3.1% chance of exploitation in 30 days, percentile 87%
public exploits
0
none known

Summary

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.

Patch / fix

  • strategy11 formidable_form_builder 4.09.05

Exploit prediction

3.13% chance of exploitation in the next 30 days, higher than 87% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • wpscan.com https://wpscan.com/vulnerability/b57dacdd-43c2-48f8-ac1e-eb8306b22533 referenced PoC, tagged "exploit" by a source, unverified
  • github.com https://github.com/S1lkys/XSS-in-Formidable-4.09.04/blob/main/XSS-in-Formidable-4.09.04.pdf referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

Affected products

  • Unknown Formidable Form Builder – Contact Form, Survey & Quiz Forms Plugin for WordPress

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-352 Cross-Site Request Forgery
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.