CVE-2025-56218

Critical

Published: 17 October 2025

Published

17 October 2025

Modified

27 October 2025

KEV Added

—

Patch

—

CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0015 34.6th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2025-56218 is a critical-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability in Ascertia Signinghub. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 34.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 3 other techniques. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

SI-10 directly requires validation of uploaded files to block crafted PDFs that enable arbitrary code execution.

SI-9 Information Input Restrictions good match

prevent

SI-9 enforces restrictions on file types and inputs to prevent unrestricted uploads of dangerous files like malicious PDFs.

SI-2 Flaw Remediation good match

prevent

SI-2 mandates timely remediation of the specific flaw in SigningHub v8.6.8 to eliminate the arbitrary file upload vulnerability.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1566.001 Spearphishing Attachment Initial Access

Adversaries may send spearphishing emails with a malicious attachment in an attempt to gain access to victim systems.

attack.mitre.org →

T1566.002 Spearphishing Link Initial Access

Adversaries may send spearphishing emails with a malicious link in an attempt to gain access to victim systems.

attack.mitre.org →

T1566.003 Spearphishing via Service Initial Access

Adversaries may send spearphishing messages via third-party services in an attempt to gain access to victim systems.

attack.mitre.org →

Why these techniques?

Arbitrary file upload vulnerability in web-based SigningHub enables exploitation of a public-facing application (T1190) and facilitates spearphishing via service (T1566.003) by uploading crafted files (Excel/PDF with scripts or disguised phishing URLs) that are converted and delivered to recipients, leading to malicious file (T1566.001) or link (T1566.002) execution upon interaction.

NVD Description

An arbitrary file upload vulnerability in SigningHub v8.6.8 allows attackers to execute arbitrary code via uploading a crafted PDF file.

Deeper analysisAI

CVE-2025-56218 is an arbitrary file upload vulnerability in SigningHub version 8.6.8 that enables attackers to execute arbitrary code by uploading a crafted PDF file. This issue, published on 2025-10-17, is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type) and carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), marking it as critical due to its high impact on confidentiality, integrity, and availability.

Unauthenticated remote attackers can exploit this vulnerability over the network with low attack complexity and no user interaction required. By uploading a specially crafted PDF file, attackers achieve arbitrary code execution on the targeted SigningHub instance, potentially leading to full system compromise.

Mitigation guidance and further details are available in vendor advisories from Ascertia (http://ascertia.com), SigningHub (http://signinghub.com), and the GitHub repository documenting the vulnerability (https://github.com/saykino/CVE-2025-56218).