External risk intelligence

PDF Signer Server-Side Template Injection RCE via CSRF Cookie

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2019-25729

The product is designed for online digital signatures and document processing. Such applications are typically deployed as public-facing web services or portals to allow users to upload, sign, and manage PDF documents over the internet.

Cross-site Request Forgery

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 vulnerability has been identified in a PDF signing technology that could allow attackers to execute commands on affected servers. This issue stems from a server-side template injection flaw within the application's handling of specific cookie parameters, potentially enabling unauthorized access to sensitive information. The main concern is to confirm if this specific technology is in use and exposed to external threats.

Unauthenticated attackers can run commands on servers.
It impacts systems processing digital signatures online.
Confirm relevance and exposure to sensitive data.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted request to the affected server. This request would involve manipulating the CSRF-TOKEN cookie parameter to inject a server-side template payload, ultimately leading to the execution of arbitrary code.

No authentication or user interaction required.
Inject PHP commands via CSRF-TOKEN cookie.
Arbitrary code execution and data theft.

Live Threat

Current exploitation, exposure, and threat context

Unauthenticated attackers could execute arbitrary code on the server by exploiting a server-side template injection vulnerability. This could occur when an attacker crafts a malicious `CSRF-TOKEN` cookie containing PHP commands, potentially allowing them to retrieve sensitive information.

Server system and data at risk.
Malicious PHP commands injected via cookie.
Arbitrary code execution and data access.

Operational Fix

Recommended remediation, mitigation, and detection steps

The server-side template injection vulnerability in PDF Signer likely affects organizations using it for online digital signatures and document processing. Responsibility typically falls to application owners or platform teams to identify instances, assess business criticality and reachability, and then plan remediation.

Application owners should prioritize investigation.
Verify exposure and business impact.
Plan vendor coordination for remediation.

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 PDF Signer 3.0?

PDF Signer 3.0 is a web-based software tool designed to facilitate the digital signing and management of PDF documents online. It is typically deployed as a server-side application that allows users to upload, process, and cryptographically secure documents directly through a web browser interface.

What is the vulnerability in CVE-2019-25729?

This vulnerability is a Server-Side Template Injection (CWE-352). It occurs when an application improperly treats user-supplied data as executable code. In this specific case, the software fails to sanitize input in the CSRF-TOKEN cookie, allowing a remote attacker to inject and run unauthorized PHP commands on the server.

How does an attacker trigger this flaw?

An attacker triggers this by sending a crafted HTTP request to the server where the CSRF-TOKEN cookie is manipulated to include malicious PHP code. The vulnerability does not require the attacker to be authenticated or interact with other users. Simply sending the malicious request to the web service is sufficient to execute the code; it is not triggered by normal, non-malicious browsing behavior.

Is my instance of PDF Signer at risk?

According to Halo Surface Signal, this software is often deployed as a public-facing web service to enable remote document signing, making internet-exposed instances high-risk. If your PDF Signer 3.0 installation is reachable from the internet, it is likely accessible to these unauthorized commands, increasing the urgency to assess your specific deployment.

What steps should I take if I use this software?

Application owners should immediately verify if PDF Signer 3.0 is running in their environment and determine its network accessibility. Once identified, assess the business criticality of the system, restrict public access if possible, and coordinate with the software vendor for available updates or guidance to secure the affected cookie handling mechanism.

References

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.