NetSupport Manager - Insecure by Default

NetSupport Manager exposes hundreds of machines to remote takeover

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Here’s the latest from our TRU Team…

In a recent intrusion investigation conducted by eSentire’s incident handling team, the laptop of a work-from-home user was compromised via a remote-control software called NetSupport Manager. The software had been legitimately installed by the IT team to facilitate remote support and administration, but unexpected circumstances left the machine exposed to attackers on the Internet.

The circumstances involved two factors that were not anticipated by the IT team when they deployed the software:

• By default, NetSupport Manager requires no authentication when accepting remote control connections.
• The user’s laptop was plugged into a home router that was configured to expose the NetSupport Manager service port (tcp/5405) to the public Internet.

Our incident handlers were able to confirm this state of affairs by downloading a trial version of the NetSupport software and using it to connect to the compromised laptop via the public IP address of the user’s home router. No credentials were necessary to gain control of the user’s desktop.

The NetSupport Manager component that listens for and handles incoming remote-control sessions is called the Client. During initial installation via the InstallShield Wizard, the Client is installed in a listening state ready to accept connections on TCP port 5405.

Unless an extra step is performed using a separate application (the NetSupport Client Configurator component), the Client will allow unauthenticated remote-control connections, leaving the host in a vulnerable state. 

The lack of authentication by default is documented in a knowledge base article by the vendor, but neither the setup wizard nor the Getting Started guide make it sufficiently clear that extra steps via a separate application are necessary to enable authentication.

Insecure Default Configuration

When the NetSupport Manager service is deployed manually via the InstallShield Wizard, there are three setup types to choose from: Typical, Client, and Custom (Figure 1). In all cases (if the Client component is included in the custom setup options), the installation concludes with the host in a vulnerable state.

No indication is given to the user that a separate step in the Client Configurator component is required to set up the authentication for the remote-control sessions.

The Configurator can operate in two modes: Basic and Advanced. In Basic mode, the configurator allows a pre-shared key (called Client Security Key) to be set. If the key doesn’t match on both sides of the connection, the attempt will fail.

Alternatively (or in addition to the security key), a user password can be set so the remote user will be prompted before a session can be established. Once these security options are configured, the Configurator app restarts the client for the new settings to take effect.

In Advanced mode, the Configurator app allows more flexible user authentication options to be set, including integrated Windows authentication, Active Directory authentication, and RADIUS authentication (Figures 2-3).

Scanning For Misconfigured NetSupport Clients

Since it is very easy to leave a NetSupport Client in a vulnerable state, we decided to perform an Internet-wide scan to determine how prevalent such vulnerable configurations are in the wild. An Nmap version scan of the public IPv4 address space revealed 542 publicly accessible NetSupport clients on TCP port 5405 (Figure 4).

Of these, over 20% (111 hosts) were found to require no authentication whatsoever. The scanning can be automated via NetSupport Manager’s custom scripting engine, which provides a VB.NET-like domain-specific scripting language to automate various tasks (Figure 5).

Recommendations from the Threat Response Unit (TRU)

It is clear that the insecure default configuration of NetSupport clients leads to a high rate of unintended misconfigurations in the wild. Our scan of the public IPv4 address space indicates that over 20% of publicly accessible NetSupport clients allow remote access with no authentication whatsoever.

Attackers seem to be aware of this issue, since a lab host we intentionally left exposed to the public was found by an attacker in less than an hour, suggesting that threat actors are continuously scanning for vulnerable NetSupport clients to exploit.

Therefore, we strongly recommend:

• Users of NetSupport Manager software should review the authentication settings of their managed hosts. Even if the hosts are not usually exposed to the Internet, unexpected circumstances can leave these hosts accessible to external threat actors, as it happened in the incident that triggered our investigation.
• At minimum, a strong pre-shared key should be configured on all hosts running a NetSupport client on internal LANs.
• Hosts that are intended to be remotely managed via the Internet should utilize stronger forms of authentication, including the use of 2FA via a Gateway Server.
• Audit your environment regularly to ensure all endpoints are patched with the latest vendor security updates.
• Protect endpoints against malware by:
  • Ensuring antivirus signatures are up-to-date.
  • Using a Next-Gen AV (NGAV) or Endpoint Detection and Response (EDR) tool to detect and contain threats.

eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.

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