External risk intelligence

Jacqueline Theme PHP Object Injection Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-78531

The vulnerability affects a WordPress theme, which is typically deployed as a public-facing web application. Web applications are commonly accessible from the internet to serve content or interact with users, making the vulnerable code path reachable in standard, real-world 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

A critical vulnerability has been identified in the Jacqueline theme, potentially allowing unauthenticated attackers to inject malicious code through PHP object injection. This could allow unauthorized access and control over affected systems. The main concern is confirming relevance and exposure.

Unauthenticated code injection flaw found.
Impacts public-facing websites.
Assess business relevance and exposure.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker can exploit a PHP Object Injection vulnerability in the Jacqueline theme to execute arbitrary code on the server. This occurs when the application improperly handles serialized PHP data, allowing an attacker to inject malicious objects that are then processed by the application, potentially leading to a complete system compromise.

No authentication required.
Triggered by sending crafted serialized data.
Risk of arbitrary code execution and server compromise.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to inject malicious PHP objects into systems running Jacqueline, potentially leading to unauthorized actions. The conditions for this risk involve the presence of specific patterns within the application's input handling that trigger the object injection.

System data could be compromised.
Malicious input could be processed.
Unauthorized actions may occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

This unauthenticated PHP Object Injection vulnerability in the Jacqueline theme requires immediate attention from application owners and infrastructure teams. The first critical step is to identify all instances of the affected theme, confirm their exposure to the internet and business criticality, and assign an accountable owner for remediation planning.

Ownership: Application and Infrastructure Teams.
Verify: Public reachability and business impact.
Action: Plan remediation based on exposure.

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 Jacqueline theme?

Jacqueline is a WordPress theme commonly used to design and manage the visual layout and user experience of websites. It acts as a template layer that dictates how content is presented to visitors, operating within the WordPress ecosystem to integrate functional features and aesthetic styles for web administrators.

What does PHP object injection mean for CVE-2026-78531?

This vulnerability is classified as CWE-502, Deserialization of Untrusted Data. It happens when the theme improperly processes serialized data provided by a user. Instead of just reading the data, the application mistakenly turns that input into active PHP objects, which can allow an attacker to manipulate the program's logic and execute unauthorized code.

How can an attacker trigger this Jacqueline vulnerability?

An attacker triggers this bug by sending a specifically crafted, serialized string to the application. It does not require any user account or password to execute. However, it will not be triggered if the input handling mechanism does not contain the flawed code path, meaning the vulnerability only manifests when the theme is actively processing such malicious inputs.

Do I need to worry if my site is not internet-facing?

Halo Surface Signal indicates that since this is a WordPress theme, it is typically deployed as a public-facing application, making the vulnerable code path easily reachable. While internal-only sites have a smaller attack surface, any instance of this theme remains potentially risky if it is accessible to untrusted networks or users within your organization.

When should I prioritize responding to this CVE?

You should prioritize this immediately if you use the Jacqueline theme in versions 2.22 or older. Your first step is to create an inventory of all sites running this theme. Once identified, evaluate the criticality of the site and confirm which ones are exposed to external traffic, then assign an owner to manage the patching process to prevent potential system compromise.

References

patchstack.com/database/wordpress/theme/jacqueline/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.