External risk intelligence

Gravity Forms PHP Object Injection Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-103039

The vulnerability affects a WordPress plugin, which is typically deployed as part of public-facing web applications. Because the attack vector involves processing input from web forms that are accessible to unauthenticated users, the vulnerable surface is directly exposed to the public internet as part of the normal operation of a web-based service.

Deserialization

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in the Gravity Forms plugin for WordPress. This issue, if exploited in conjunction with other installed themes or plugins, could allow unauthenticated attackers to inject malicious code, potentially leading to remote code execution on affected systems. The main concern is confirming relevance and exposure to our WordPress environments.

PHP code injection risk in a popular WordPress plugin.
Potential for remote code execution if combined with other software.
Confirm if WordPress environments use this plugin.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by submitting specially crafted data through a form's "List" type custom field. This data bypasses proper sanitization, allowing a PHP object to be injected into post metadata. If a compatible gadget chain exists in the WordPress installation, this could lead to remote code execution.

Attacker needs no login or special access.
Triggered by submitting a form field.
Risk of remote code execution.

Live Threat

Current exploitation, exposure, and threat context

When supported by the advisory, unauthenticated attackers could inject a PHP object into post meta. This could lead to remote code execution if a gadget chain is present in an additional plugin or theme, or when the custom field is mapped to the protected `_wp_page_template` meta key, leveraging WordPress's own functions.

Unrestricted PHP object injection into post meta.
Via a Post Custom Field's List input type.
Potential for remote code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Gravity Forms plugin for WordPress requires immediate attention from the platform or web application owner. The first step is to identify all WordPress instances utilizing Gravity Forms, confirm if they are accessible externally and if the specific vulnerable feature is enabled, and then assess the business criticality of each instance to prioritize remediation. Coordination with the website owner and potentially theme/plugin developers may be necessary.

Platform/web app owners must take ownership.
Verify Gravity Forms is externally reachable.
Plan risk-based remediation strategy.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is the Gravity Forms plugin used for?

Gravity Forms is a popular plugin for WordPress sites used to build custom forms, manage data collection, and integrate user-submitted information into the WordPress database. It helps site administrators create contact forms, surveys, and complex workflows that handle input directly from visitors.

What is the vulnerability class for CVE-2026-103039?

This vulnerability is classified as PHP Object Injection (CWE-502). It occurs when untrusted user input is passed into a function that reconstructs PHP objects without sufficient safeguards. In this case, the plugin accidentally uses an insecure function instead of a hardened one, allowing an attacker to inject unauthorized objects that the application might then process as legitimate code.

How can an attacker trigger this CVE-2026-103039 flaw?

An attacker can trigger this issue by submitting specially crafted data through a form using a 'List' type custom field. The flaw does not occur if the 'List' field is not used in the form, nor does it trigger if the plugin correctly uses its internal hardened serialization function. The risk increases if the field is mapped to protected metadata, which can automatically trigger harmful behavior.

Do I need to worry if my WordPress site is internal?

Halo Surface Signal indicates this vulnerability is highly likely to affect public-facing web applications. Since the attack vector relies on unauthenticated access to web forms, sites exposed to the internet face the highest risk. If your WordPress instance is restricted to an internal network with no public access, the attack surface is significantly reduced, though you should still verify your plugin configurations.

What is the first step to address this plugin issue?

Begin by auditing your WordPress environment to identify all instances where Gravity Forms is installed and active. Determine which of these sites are reachable from the internet and whether they utilize form configurations that include 'List' type custom fields. Once identified, prioritize these public-facing installations for updates or configuration changes to mitigate the risk of object injection.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.