External risk intelligence

Hash Form PHP Object Injection Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-78292

The vulnerability affects a WordPress plugin, which is typically used to create internet-facing web forms and applications. Because these components are designed to process user input directly from the public web, they represent an externally reachable attack surface in common deployment scenarios.

Deserialization

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory details a critical vulnerability in Hash Form, a WordPress plugin, that allows for unauthenticated PHP Object Injection. This type of issue could potentially allow an attacker to execute arbitrary code on a server, leading to a significant compromise of the affected system. The main concern is confirming relevance and exposure.

A critical flaw allows unauthorized code execution.
Affects internet-facing web forms and applications.
Confirm if your systems use this plugin.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker could exploit this vulnerability by sending specially crafted data to a web application that uses the affected component. This could allow the attacker to inject malicious PHP objects, potentially leading to code execution or unauthorized access to the system.

No authentication required.
Triggered via specially crafted input.
Leads to code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to inject malicious PHP objects into a system running Hash Form. When supported by the advisory, this could lead to the execution of arbitrary code, potentially impacting the confidentiality, integrity, and availability of the affected system.

System data could be at risk.
Through crafted requests to the application.
Arbitrary code execution and system compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

This unauthenticated PHP Object Injection vulnerability in Hash Form impacts systems using affected versions, particularly those with internet-facing web forms. The first practical move is to identify all instances of the vulnerable plugin, confirm its exposure to the internet, and determine business criticality to prioritize remediation efforts.

Application owners should own this issue.
Verify internet reachability and business criticality.
Plan phased remediation based on risk.

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.

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Frequently asked questions

What is the Hash Form plugin?

Hash Form is a plugin for WordPress designed to help site administrators build and manage web forms. It typically handles user-submitted data, such as contact details or survey responses, directly within the WordPress ecosystem to support interactive features on a website.

What does PHP Object Injection mean for CVE-2026-78292?

This vulnerability, classified as CWE-502 (Deserialization of Untrusted Data), occurs when the plugin improperly handles serialized data. By sending a malicious PHP object, an attacker can manipulate the application's logic. If successful, this can lead to arbitrary code execution, allowing unauthorized commands to run on the server hosting the WordPress site.

How is this vulnerability triggered?

An attacker triggers the flaw by sending a specially crafted request containing malicious data to the Hash Form plugin. No interaction from an authorized user or administrator is required to initiate the attack. However, simply visiting the site or loading legitimate form data does not trigger the bug; the attacker must intentionally submit specific, malicious payload structures that the plugin then incorrectly processes.

Is my site at risk according to Halo Surface Signal?

Halo Surface Signal indicates that because Hash Form is used to process user input from the public web, it is considered internet-facing. This design makes the component inherently reachable from the outside. If your WordPress site uses this plugin and is accessible to the public, your installation presents a high-visibility surface for potential attackers.

Do I need to take action if I use Hash Form?

Yes. Start by creating an inventory of all WordPress instances where Hash Form is installed to understand your footprint. Once identified, evaluate which sites are accessible over the internet and assess their business importance. Use this information to prioritize which sites need immediate attention, focusing on those most critical to your operations.

References

patchstack.com/database/wordpress/plugin/hash-form/vulnerability/wor…

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.