External risk intelligence

SigningHub Arbitrary File Upload Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-56218

SigningHub is an enterprise platform designed for digital signatures and document workflows, which are commonly deployed as internet-facing web applications or portals to facilitate external document signing and authentication processes.

Unrestricted File Upload

Ascertia Signinghub

8.6.8 and earlier

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 highlights a critical vulnerability in SigningHub, a system used for digital signatures and document workflows. The issue allows for the execution of arbitrary code through a crafted PDF upload, which could have significant implications for data integrity and system control if the affected technology is in use.

Attackers can upload malicious files to gain control.
Matters if digital document signing is used.
Confirm if our SigningHub instances are affected.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by uploading a specially crafted PDF file to the SigningHub application. This would bypass security checks and allow the attacker to execute arbitrary code on the server, potentially leading to a full system compromise.

No special access required.
Upload a malicious PDF file.
Remote code execution and system compromise.

Live Threat

Current exploitation, exposure, and threat context

A critical vulnerability in SigningHub could allow an unauthenticated attacker to upload a malicious PDF file. If successful, this could lead to the execution of arbitrary code on the affected system, potentially compromising its integrity and confidentiality.

System code execution.
Via crafted PDF upload.
Compromise of system integrity.

Operational Fix

Recommended remediation, mitigation, and detection steps

Identifying the presence and criticality of SigningHub instances is the immediate priority for application owners and infrastructure teams. The first practical step is to locate all deployments, determine their external reachability and business impact, and then assign ownership to a specific team for coordinated remediation planning.

Application owners should oversee this issue.
Verify external accessibility and business criticality.
Plan remediation based on identified 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.

Free EASM Trial See How Signal Works

Frequently asked questions

What is SigningHub?

SigningHub is an enterprise platform developed by Ascertia that handles digital signatures, identity verification, and secure document workflows. Organizations use it as a centralized hub to facilitate electronic signing processes, often integrating it into web portals to allow both internal staff and external partners to sign and authenticate important documents digitally.

How does CVE-2025-56218 allow code execution?

This vulnerability involves an arbitrary file upload flaw, categorized as CWE-434. It occurs when an application improperly validates the type or content of uploaded files. In this specific case, the software fails to adequately restrict the files users can upload, enabling an attacker to submit a maliciously crafted PDF that, when processed, tricks the server into executing unauthorized code.

Do I need special access to trigger this bug?

No, this vulnerability does not require authentication or special user privileges to exploit. An attacker only needs the ability to interact with the file upload functionality exposed by the application. Uploading standard, non-malicious documents through the intended web interface does not trigger the vulnerability; it specifically requires the submission of a file crafted to bypass security checks.

Is my SigningHub instance at risk?

Halo Surface Signal indicates that SigningHub instances are frequently deployed as internet-facing web portals to support external signing workflows, making them potentially reachable by unauthorized parties globally. If your deployment is accessible from the public internet, the risk level is higher because attackers do not need to be on your internal network to attempt to upload a malicious file.

What should I do to respond to this CVE?

Start by identifying all instances of SigningHub within your infrastructure. Once located, determine if these servers are reachable from the internet and evaluate their business criticality. Assign a dedicated owner to each instance to oversee the remediation process and coordinate with your technical teams to apply necessary patches or vendor-provided updates to secure the platform.

References

github.com/saykino/CVE-2025-56218

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.