Executive Summary

CVE-2018-25239 is a denial of service vulnerability in Microsoft Smart VPN version 1.1.3.0. It occurs because the application does not properly handle oversized input submitted through its search interface.

Specifically, a local attacker can paste a buffer of 2100 characters into the top-right search bar, which triggers an unhandled exception and causes the application to crash.

This vulnerability arises from unsafe reflection where externally controlled input is used to select classes or code, leading to the crash.

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Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS) condition.

An attacker with local access can cause the Microsoft Smart VPN application to crash by submitting an oversized input, making the application unresponsive and unavailable.

This can disrupt VPN connectivity and potentially affect any dependent services or workflows relying on the application.

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Detection Guidance

This vulnerability can be detected by attempting to reproduce the crash condition locally on the affected system running Microsoft Smart VPN version 1.1.3.0.

A practical detection method involves submitting an input buffer of 2100 characters into the application's top-right search bar to see if it triggers an unhandled exception and crashes the application.

For example, you can create a text file containing 2100 'A' characters and paste its content into the search bar.

A simple command to generate such a file on a system with Python installed is:

• python -c "print('A' * 2100)" > PoC.txt

Then open PoC.txt, copy the content, and paste it into the Smart VPN search bar to test if the application crashes.

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Mitigation Strategies

To mitigate this vulnerability immediately, avoid submitting oversized inputs (specifically inputs of 2100 characters or more) into the Smart VPN search interface.

Restrict local access to the application to trusted users only, since the attack requires local interaction.

Monitor for application crashes and restart the application if it becomes unresponsive.

Check for updates or patches from the software vendor that address this vulnerability and apply them as soon as they become available.

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Compliance Impact

The vulnerability in Microsoft Smart VPN 1.1.3.0 is a denial of service (DoS) issue that allows local attackers to crash the application by submitting oversized input. It does not impact confidentiality or integrity, only availability.

Since the vulnerability does not lead to data breaches or unauthorized data access, it does not directly affect compliance with data protection regulations such as GDPR or HIPAA, which primarily focus on protecting personal and sensitive data confidentiality and integrity.

However, the denial of service could impact availability, which is a component of some compliance frameworks. Organizations relying on Microsoft Smart VPN might need to consider this availability risk in their overall compliance and risk management strategies.

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