CVE-2026-86833

MetForm <= 4.3.0 - Unauthenticated Arbitrary HTML Injection in Notification Emails

2026-10-01 00:00

Strategic Overview

Status: Patched in 4.3.1
Affected Plugin: MetForm – Contact Form, Survey, Quiz, Conditional Forms, Form Templates & Custom Form Builder for Elementor
Affected Version: <= 4.3.0
CVSS: 4.7Medium
Weakness type: CWE-20 · Improper Input Validation
CVE: CVE-2026-86833

View all MetForm – Contact Form, Survey, Quiz, Conditional Forms, Form Templates & Custom Form Builder for Elementor vulnerabilities

At a glance

CVE-2026-86833 is a medium-severity Improper Input Validation vulnerability in the MetForm WordPress plugin, affecting versions <= 4.3.0. It carries a CVSS score of 4.7 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 4.3.1; sites on affected versions should update now. Disclosed October 2026, reported by vuxvinh.

Vulnerability Overview

The MetForm plugin for WordPress is vulnerable to HTML Injection in all versions up to, and including, 4.3.0. This is due to insufficient output escaping on user-submitted field values before they are substituted into the HTML email body via the Metform_Shortcode::get_process_shortcode() function. This makes it possible for unauthenticated attackers to inject arbitrary HTML markup into administrator and submitter notification emails sent by the site.

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.

CWE-20: Improper Input Validation

MetForm <= 4.3.0 carries this weakness at get_process_shortcode(), and reaching it takes no account at all. Improper input validation means the application accepts input without confirming it has the form, type or range the code downstream assumes.

The concrete impact depends on where the unvalidated value lands, which is why records in this class range from cosmetic bugs to full compromise. For MetForm the fix is 4.3.1: builds <= 4.3.0 are affected, anything from 4.3.1 onward is not.

Remediation

Update to version 4.3.1, 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: MetForm 4.3.1 closes this, and updating the plugin is the step that ends it.

Firewall
Login Security
Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-86833 https://www.wordfence.com/threat-intel/vulnerabilities/id/2f50874b-5623-4f4f-be50-9a8090a73c4f https://nvd.nist.gov/vuln/detail/CVE-2026-86833

Related records

Other vulnerabilities in MetForm – Contact Form, Survey, Quiz, Conditional Forms, Form Templates & Custom Form Builder for Elementor

CVSS Vector

4.7

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

Base

Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredNone
User InteractionRequired
ScopeChanged
ConfidentialityNone
IntegrityLow
AvailabilityNone

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