VNC Is The Hacker’s New Remote Desktop Tool For Cyber Attacks

While facilitating remote work, remote desktop software presents security challenges for IT teams due to the use of various tools and ports.

The multitude of ports makes it difficult to monitor for malicious traffic. 

Weak credentials and software vulnerabilities are exploited to gain access to user systems.

Hackers may also use technical support scams to trick users into granting access.  

The Most Targeted Remote Desktop Tools In The Last 12 Months

Researchers identified VNC, a platform-independent remote desktop tool using RFB protocol, as the most targeted remote desktop application (98% of traffic).

The attacks leveraged weak passwords and a critical vulnerability (CVE-2006-2369) in RealVNC 4.1.1, allowing authentication bypass. 

Over 99% of attacks targeted unsecured HTTP ports rather than TCP ports used for application data exchange, which suggests attackers exploit the inherent lack of authentication on HTTP for unauthorized access.

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The security of VNCs varies depending on the specific software, while some offer weak password limitations, others leverage SSH or VPN tunnelling for encryption.

VNC uses a base port (5800 for TCP, 5900 for HTTP) with an additive display number, making it difficult to secure with firewalls compared to single-port remote desktop solutions. 

Additionally, pinpointing the origin of VNC attacks is challenging due to attackers using proxies and VPNs, but a significant portion seems to originate from China. 

Attackers target RDP, a remote desktop protocol, for credential-based attacks and exploit vulnerabilities to execute malicious code, as RDP is more likely to be involved in large attacks compared to VNC. 

Flaws Exploited

In one study, 15% of RDP attacks leveraged obsolete cookies, possibly to target older, more vulnerable RDP software,  and RDP vulnerabilities like CVE-2018-0886 (targeting credential security), CVE-2019-0708 (with worm potential), and CVE-2019-0887 (hypervisor access) have been reported by Barracuda. 

Attackers exploit vulnerabilities in RDP to gain access to systems. Brute-force attacks are common, targeting password hashes for privileged accounts. RDP can also be used to launch denial-of-service attacks. 

In social engineering scams, attackers convince users to grant RDP access to fix fake technical problems, and vulnerable RDP instances are sold on the black market for further attacks.

North America is a leading source of RDP attacks, but location tracking is difficult due to anonymizing techniques. 

TeamViewer, a remote desktop tool, rarely encounters attacks (0.1% of traffic). Recent versions target enterprises and integrate with business applications, offering security features like fingerprinting, strong password enforcement, and multi-factor authentication. 

Encrypted communication channels further enhance security. However, phished credentials and technical support scams can still compromise TeamViewer sessions and may use ports beyond the primary port 5938, making malicious traffic detection more challenging for security teams. 

Citrix created ICA as an alternative to RDP. It uses ports 1494 and 2598, while older ICA clients and the ICA Proxy have had RCE vulnerabilities. 

AnyDesk, another RDP solution, uses port 6568 and has been abused in tech support scams and malware, while Splashtop Remote, using port 6783, has been involved in support scams and can be compromised through weak credentials.

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