A Single Line of Markdown Can Wreck the Server: What Is the CVE-2025-65108 Vulnerability Hiding?

Description of CVE-2025-65108

For those who don't know, Markdown is a simple markup language used to format text with easy-to-remember and easy-to-type characters. It is designed to be:

• Easy to read in plain text.

• Easy to write.

• Easy to convert to HTML, PDF, and other formats.

To understand better, I'll show you some special characters that are easy to use in Markdown, such as:

Because of its convenience, Markdown is widely used by developers, document writers, and bloggers, which also makes it a potential target for vulnerabilities that attackers want to exploit. In November 2025, cybersecurity experts identified a new vulnerability labeled CVE-2025-65108, rated CVSS 10.0 – absolute danger level, revealing that just a piece of front-matter in Markdown can open the door to Remote Code Execution.

This vulnerability is not just a software bug; it highlights the thin line between "text formatting" and "malicious code execution." If you are using tools to convert Markdown to PDF in your system, this could be a ticking time bomb silently counting down...

Scope of Impact

Any environment that converts Markdown to PDF using the md-to-pdf library (all versions before 5.2.5) is at risk of exploitation.

The impact scope of CVE-2025-65108 is not limited to web applications but extends to the entire ecosystem, including:

• Dev tools,

• Automation pipelines,

• Cloud services,

• Internal infrastructure.

Wherever untrusted Markdown is converted to PDF, this vulnerability can become a dangerous RCE vector.

Severity Assessment

CVE-2025-65108 is rated as CRITICAL with the following scores:

• NIST: NVD Base Score: N/A - NVD assessment not yet provided.

• CNA: Patchstack Base Score: 10.0 - CRITICAL Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Analysis and Exploitation of the Vulnerability

First, as mentioned, the attacker will prepare an executable payload, and it can only occur when one of the following conditions is met:

• A plugin/extension in the md-to-pdf pipeline is enabled, and that plugin actively executes JavaScript code blocks in the Node context (for example, plugins like remark-exec / rehype-run or a custom plugin that calls eval, vm.runInThisContext, new Function, or require on the code block content).

• md-to-pdf (or a dependency) contains a vulnerability that allows injecting/executing Node code from the markdown content (for example, using a template engine with unsafe interpolation like _.template or handlebars without sanitizing).

• The user runs md-to-pdf with custom configurations that allow running hooks or scripts taken from the Markdown content.

After preparing a payload as mentioned, the attacker will introduce this file into the system in several ways: upload, commit PR, send an email, or pass it into an API. Here, when the user activates md-to-pdf to convert the file, the parser reads the front-matter and evaluates.

As you can see, ---javascript and ---RCE here are not standard front-matter (front-matter is usually ---\nkey: value\n---) and are being exploited to execute the attack. The function ((require("child_process")).execSync("calc.exe")) will be called - this is a JavaScript command running in the Node.js environment.

• require("child_process") gets the child_process module.

• .execSync("calc.exe") runs the system command calc.exe synchronously - on Windows, this will open the Calculator. On Linux/Mac, this command will return an error if calc.exe does not exist.

The goal of the payload: if this JS code is executed in the Node.js context (not in the browser), it will call the subsystem and execute the command - which means local RCE (remote code execution). A dangerous point here is that if the server runs with high privileges (root/Administrator), the consequences are more severe (full system access).

Once an attacker has executed code on the system (e.g., RCE through the payload as you analyzed earlier), the post-exploitation steps usually aim to:

• Maintain access

• Privilege escalation

• Cover tracks

• Gather information/data

• Expand reach

• Prepare for sabotage or deploy ransomware

Recommendation

1. Update to md-to-pdf version ≥ 5.2.5

   • Check the current version of md-to-pdf:

     • npm list md-to-pdf

     • yarn list md-to-pdf

   • Update using npm

     • npm install md-to-pdf@^5.2.5

     • npm install md-to-pdf@latest

   • Update using Yarn

     • yarn add md-to-pdf@^5.2.5

   • Update in package.json

     • "md-to-pdf": "5.0.x" => "md-to-pdf": "^5.2.5"

     • npm install

   • Update md-to-pdf in Docker or container

     • RUN npm install md-to-pdf

     • docker build -t app:patched

2. Prevent untrusted Markdown processing

   • Temporarily stop services that automatically convert Markdown to PDF if the input comes from external users.

   • Only process documents from trusted sources while waiting for updates.

3. Use only trusted Markdown sources

   • Do not download or open Markdown files (.md) from unclear sources.

   • Do not copy/paste strange Markdown content into PDF conversion systems.

   • Avoid using Markdown templates shared over the Internet if the source is not verified.

4. Check front-matter before opening or uploading Markdown

   • If you see sections like:

     

     

     or content with unusual keywords such as:

     • child_process

     • execSync

     • require(

     • process.mainModule

   • Stop processing immediately, as this could be a payload designed to exploit an RCE vulnerability.

5. Do not share or upload sensitive Markdown to untrusted online services

   • Do not upload Markdown files containing internal information to free services that cannot be verified for safety.

   • Use the organization's official platform to create PDFs.

Summary

The vulnerability CVE-2025-65108 reveals an unsettling truth: even seemingly harmless tools like Markdown to PDF converters can become the starting point for a full-scale attack. Injecting JavaScript through front-matter and executing code within md-to-pdf has turned a simple document processing task into a serious RCE point, rated CVSS 10.0 – the highest possible level.

The impact spreads widely, from web applications to CI/CD pipelines, from cloud services to internal systems. This creates an urgent need to update versions, review the entire Markdown processing workflow, and apply safe isolation measures for document conversion tasks.

CVE-2025-65108 is not just a vulnerability; it's a reminder that the line between "data" and "executable code" is always fragile. A single misconfiguration or an overlooked feature is enough for an attacker to turn a Markdown document into a weapon. Acting early is crucial to limit risks and protect systems from unforeseen consequences.

References

1. Critical Markdown to PDF Flaw (CVE-2025-65108, CVSS 10.0) Allows RCE via JS Injection in Markdown Front-Matter

2. NVD - CVE-2025-65108

3. md-to-pdf vulnerable to arbitrary JavaScript code execution when parsing front matter · CVE-2025-65108 · GitHub Advisory Database · GitHub