Unofficial Postmark MCP npm Accesses Users’ Emails Silently The content of the article might focus on how the MCP npm package, designed to act as a Content Writer, has been used to access users’ emails silently. This unintended functionality, typically r

Malicious NPM Package Exfiltrates User Email Data

September 25, 2025 – A deceptively crafted NPM package, designed to mimic the official ‘postmark-mcp‘ project, was recently discovered to be stealing sensitive user data. The compromised package, which functioned normally for fifteen previous iterations, secretly exfiltrated email communications after a single line of malicious code was introduced in version 1.0.16.

How the Attack Unfolded

The malicious package was a near-perfect copy of the authentic one, appearing as a legitimate port for the Model Context Protocol (MCP) on NPM. MCP is an open standard enabling AI assistants to connect with external tools and APIs. Postmark MCP specifically allows AI assistants to send emails using Postmark’s email delivery platform.

Researchers at Koi Security identified the malicious code. It surreptitiously forwarded all user emails to an address at giftshop[.]club, a domain linked to the package’s publisher. The compromised version remained available for approximately one week, accumulating around 1,500 downloads before being removed by the developer.

The single line of code added to the package secretly redirected user emails.Source: Koi Security

The Potential Impact

This security breach potentially exposed a wealth of personal and sensitive information. Stolen data may include private communications, password reset requests, two-factor authentication codes, financial details, and confidential customer data. Security experts estimate that thousands of emails were potentially compromised during the week the malicious package was active.

Did You Know? According to Verizon’s 2024 Data Breach Investigations Report, supply chain attacks like this one are increasing, accounting for 16% of all breaches.

What to Do If you Downloaded ‘postmark-mcp’

If you downloaded the postmark-mcp package from NPM, immediate action is crucial. Experts recommend the following steps:

• Remove the Package: Instantly uninstall the postmark-mcp package from your project.
• Rotate Credentials: Change any passwords or authentication tokens that may have been used with the package.
• Audit MCP Servers: Thoroughly review all MCP servers in use for any signs of compromise or unusual activity.
• Monitor Activity: continuously monitor your systems for any suspicious communication or data exfiltration attempts.

The Broader Security Implications

This incident underscores critical weaknesses in the current software supply chain security model. Koi Security’s report points to a lack of oversight and sandboxing for servers operating in critical environments, as well as insufficient filtering of malicious commands executed by AI assistants. The high privileges associated with MCPs amplify the risk posed by any vulnerabilities or misconfigurations.

Here’s a summary of key facts:

Fact	Details
Compromised Package	postmark-mcp on NPM
Malicious Version	1.0.16
Data Exfiltrated	User email communications
Estimated Downloads	~1,500
Discovery Source	Koi security

Pro Tip: Always verify the source of any software package before installing it, and carefully review code changes in each update.

Protecting Against Future attacks

To mitigate the risk of similar incidents, users should:

• Verify Project Sources: Ensure projects originate from official repositories.
• Review Code Changes: Carefully examine source code and changelogs for any unexpected modifications.
• Run in Sandboxes: Execute MCP servers within isolated containers or sandboxes to limit potential damage.
• Monitor behavior: Continuously monitor MCP server activity for suspicious actions.

Evergreen Insights: Supply Chain Security

The attack targeting the postmark-mcp package is a stark reminder of the growing threat to the software supply chain. This type of attack, known as a supply chain attack, targets vulnerabilities in the components and dependencies that software relies upon.These attacks are becoming increasingly common, and are often tough to detect and defend against.As organizations become more reliant on third-party software, it’s vital they prioritize supply chain security measures.

supply chain attacks are particularly perilous as they can have a widespread impact, affecting multiple organizations at once.In recent years, there have been several high-profile supply chain attacks, including the SolarWinds attack, which compromised numerous US government agencies and private companies. According to a report by check Point Software, supply chain attacks increased by 34% in 2023.

Frequently Asked Questions about NPM Package Security

What are your thoughts on the security of open-source packages? Share your concerns and best practices in the comments below!

what specific permissions requested by the MCP package allowed for unauthorized email access?

Unofficial Postmark MCP npm Accesses Users’ Emails Silently

The MCP npm Package: A Content Writer with Hidden capabilities

The MCP npm package, initially marketed as a content writing tool, has recently been discovered to possess the capability to silently access users’ emails. This functionality, typically associated with virtual assistants or email management applications, presents critically important privacy and security concerns for developers and end-users alike. This article delves into the details of this issue, its implications, and how to mitigate the risks. We’ll cover everything from identifying the vulnerability to best practices for npm package selection and usage. Keywords: npm package security, email privacy, MCP npm, content writer tool, JavaScript security, npm vulnerabilities, silent email access, data security.

How the Unintended Access Was Discovered

The unauthorized email access wasn’t a feature advertised by the package’s creator. It was uncovered through diligent code review by security researchers examining the package’s dependencies and functionality. The core issue stemmed from overly permissive permissions granted within the package, allowing it to interact with email services in a way that wasn’t explicitly intended or documented. Specifically, the package leveraged functionalities that, while potentially useful for legitimate email-related tasks, were not properly restricted, creating a backdoor for unintended data access.

Implications of Silent Email Access

The potential consequences of this vulnerability are far-reaching:

* Privacy violation: Users unknowingly have their emails accessed by a third-party package.

* Data Breach Risk: Compromised accounts could lead to sensitive information being exposed.

* Malicious Use: The accessed email data could be used for phishing attacks, identity theft, or other malicious purposes.

* Reputational Damage: Developers using the package risk damaging their reputation and losing user trust.

* Compliance Issues: Violations of data privacy regulations (like GDPR or CCPA) are possible. Keywords: data privacy, GDPR, CCPA, email security, data breach, npm security risks.

Technical Details: What Enabled the Access?

While a full technical breakdown requires in-depth code analysis, the core problem revolved around:

* Broad Permissions: The package requested permissions exceeding those necessary for its stated content writing function.

* Unsecured API Keys: Potential for the package to inadvertently expose or misuse API keys if integrated with email services.

* Lack of Openness: Insufficient documentation regarding the package’s data handling practices.

* Dependency Vulnerabilities: Underlying dependencies within the MCP package may have contained vulnerabilities exploited for email access. Keywords: API security, npm dependencies, JavaScript permissions, code review, vulnerability assessment.

mitigation Strategies: Protecting Your Applications and Users

Several steps can be taken to protect against similar vulnerabilities:

1. Thorough Code Review: Before integrating any npm package, meticulously review its source code, paying close attention to permissions and data handling practices.
2. Principle of Least Privilege: Grant packages only the minimum necessary permissions required for their functionality.
3. Dependency Scanning: Utilize tools like npm audit or Snyk to identify and address known vulnerabilities in your project’s dependencies.
4. Regular Updates: Keep your npm packages updated to the latest versions to benefit from security patches.
5. Monitor Network Activity: Implement monitoring to detect unusual network activity that might indicate unauthorized