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Discovering Dropbox On Your Network

Why is "Cloud Storage" So Appealing?

Services such as DropBox use the cloud to enable users to share files with others and transfer work from office to home and back. The challenge is two-fold:

  1. Determine how this and other cloud-based technologies align with the organization’s security policies and compliance mandates.
  2. Monitor use of these solutions to ensure compliance and limit exposure while preserving benefit.

Users often turn from sanctioned file sharing methods when they reach the limits of email and internal file sharing capacity, performance, and functionality. Email was not intended to share large files, and very often restrictions are implemented on the size of an individual email and how large your inbox can grow. Users can put files on an internal file sharing service, but that limits access to local users and VPN connected users. Employees who travel or third-parties may not have access to the internal network to retrieve the files. Many IT departments do not offer an easy way to share files through more traditional methods such as public FTP servers because of security concerns.

Dropbox overcomes many of these issues and has become quite popular, as evidenced by a recent influx of $250 million additional dollars in funding. The price is right too, as you can get 2GB of storage for free and manage access to your files.

The problem is, DropBox security and usage often violate corporate policy and security best practice. Corporate policy must protect sensitive information, such as customer data and intellectual property. If this information is being transmitted insecurely to a service such as Dropbox your policies and network defenses should detect this behavior and monitor for violations and information leakage.

For example, Dropbox relies on SSL for encryption. Several attacks released this year have been reported that can circumvent SSL security, and SSL certificate authorities have been compromised, breaking down the trust that SSL relies upon for security and integrity. Client software can become the weakest link as well, even if SSL is implemented properly. The Dropbox client software has contained vulnerabilities that, when exploited, could lead to your data in the wrong hands.

To solve this problem we need to implement encryption at the file level to protect sensitive data. I have to admit, I am a Dropbox user. However, I use it with caution and implement my own security policy. Any sensitive data is sent to DropBox using file encryption (PGP in this case). Any non-sensitive information is not encrypted and I am careful to distinguish between the two.

Enforcing Policy

Tenable's Nessus vulnerability scanner contains plugins that will allow you discover DropBox software installed on your systems and audit your network. Plugins 35717 (Windows) and 55435 (OS X) will require credentials and detect the software installation on the host. Plugin 56692 will detect the DropBox listener, and 56693 will remotely detect a DropBox installation (cross-platform):

Dropbox nessus plugin output

The Passive Vulnerability Scanner (PVS) can passively detect DropBox in use on the network as shown below:

Dropbox PVS plugin output


Software as a Service (SaaS) applications such as DropBox are valuable tools that facilitate work. However, remember that it is up to the user to implement the appropriate level of security. For organizations, try not to say "No" and prevent your users from using these services without a proper evaluation of security, scalability, support, and availability. What would it cost to implement a similar solution to DropBox internally? Most likely, it would be quite a bit cheaper to educate users how to use services securely and monitoring the network for compliance to your own policies.

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