External risk intelligence

Fetch Designs Sign-up Sheets Object Injection

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-49393

The vulnerability affects a WordPress plugin designed for sign-up sheets. Such plugins are typically deployed on public-facing websites to allow users to interact with forms or registration pages, making the service inherently internet-accessible in most common deployments.

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 concerns a critical vulnerability in the Sign-up Sheets product, specifically related to how it handles untrusted data, potentially allowing unauthorized code execution. The issue has a high severity score, indicating a significant risk if exploited. The primary concern at this stage is to determine if this product is in use and, if so, to understand its specific exposure.

Untrusted data can lead to unauthorized code execution.
Critical flaw impacts data integrity and availability.
Confirm product usage and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted request to a website using the affected software. This request would trigger a flaw in how the software handles data, potentially allowing an attacker to inject malicious code and execute it on the server. This could lead to the compromise of sensitive information or the disruption of the service.

No authentication required to trigger.
Vulnerable data deserialization process.
Enables full server takeover.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in the Sign-up Sheets plugin could allow an attacker to inject malicious objects into the application. When supported by the advisory, this could lead to unauthorized actions or data compromise when the application processes these objects.

Application data and functionality.
Through crafted input to the service.
Potential for unauthorized system changes.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the Sign-up Sheets plugin likely impacts application owners and platform teams responsible for managing WordPress sites. The initial focus should be on identifying all instances of the affected plugin, assessing their exposure and business criticality, and locating the accountable owner for remediation planning.

Application owners should own the issue.
Verify plugin reachability and business impact.
Plan remediation during maintenance windows.

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 Fetch Designs Sign-up Sheets plugin used for?

Sign-up Sheets is a WordPress plugin that enables website owners to create and manage interactive forms or registration pages. It is commonly used to facilitate scheduling, volunteer coordination, or event sign-ups directly on a site, allowing visitors to input information that the plugin processes and stores.

What does CWE-502 Deserialization of Untrusted Data mean for CVE-2025-49393?

This weakness occurs when an application takes data from an untrusted source and reconstructs it into a complex object without proper validation. In CVE-2025-49393, the plugin improperly handles this process, which allows an attacker to inject malicious objects. This can trick the server into executing unauthorized commands or code, potentially resulting in full system compromise.

How is this vulnerability triggered?

An attacker triggers this flaw by sending a specifically crafted request to the web server that hosts the plugin. Because the vulnerability exists in the data handling logic, no user authentication or prior access to the system is required to initiate the attack. Simply interacting with the plugin's input mechanism with malicious data is enough to set the process in motion.

Is my site at risk according to Halo Surface Signal?

Halo Surface Signal notes that because this is a WordPress plugin used for public registration or sign-up forms, it is usually deployed on internet-facing pages. This accessibility makes it highly likely that the plugin is reachable from the public web, increasing the risk that an attacker can reach the vulnerable code path without needing internal network access.

Do I need to take immediate action if I run Sign-up Sheets?

Your first step is to verify if you have version 2.3.2 or earlier of the Sign-up Sheets plugin installed on any of your WordPress sites. Identify the owners of these instances and assess their business criticality. Once mapped, coordinate with your technical team to prioritize these assets for remediation as soon as a security update becomes available.

References

patchstack.com/database/Wordpress/Plugin/sign-up-sheets/vulnerabilit…

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.