Researchers Warn: IP Spoofing and Tunneling Protocol Flaws Open Doors to Intranet Attacks

According to cybersecurity researcher Shu-Hao Tung, vulnerabilities in widely used tunneling protocols such as Generic Routing Encapsulation (GRE) and Virtual Extensible LAN (VXLAN) could allow attackers to infiltrate protected internal networks without valid credentials. Tung presented his findings at Black Hat USA 2025, emphasizing how these exploits leverage IP spoofing to bypass traditional defenses.

The Anatomy of the Threat: What Researchers Discovered

Shu-Hao Tung’s research highlights three primary vulnerabilities in intranet security systems:

• Unencrypted GRE Tunnels: Attackers can exploit exposed GRE endpoints by scanning networks using ICMP encapsulation techniques. Once located, forged GRE packets from external sources can inject malicious traffic directly into internal systems.
• VXLAN Learning Mode Flaw: Default configurations in Linux kernels enable ‘Learning Mode,’ which accepts incoming VXLAN packets without authentication. Attackers can populate Forwarding Databases (FDBs) with impersonated IP or MAC addresses to gain access to internal services.
• Intranet Spoofing for Stealth: Using techniques like NAT-based manipulation, attackers can disguise their presence, simulating traffic patterns that mislead incident responders and delay mitigation efforts.

These flaws are particularly concerning given the widespread dependency on GRE and VXLAN protocols in enterprise networks, cloud infrastructure, and SD-WAN deployments.

Why This Matters: The Case for Enhanced Network Security

The telecom industry is rapidly expanding its use of tunneling protocols to enable efficient, scalable networking across data centers and wide area networks. However, this newfound agility comes with inherent risks. A 2024 study by Gartner reported that over 70% of SD-WAN deployments globally rely on VXLAN tunneling, underscoring how these vulnerabilities could impact thousands of networks worldwide.

In addition, IP spoofing—once associated primarily with Distributed Denial-of-Service (DDoS) attacks—has evolved into an advanced infiltration technique. Threat actors can now remain undetected for extended periods, undermining trust in traditional monitoring systems.

For companies like Cisco, Juniper Networks, and MikroTik—whose products dominate Layer 2 and Layer 3 networking solutions—this research highlights a critical need for better protocol-level security measures. The inherent vulnerabilities in default configurations and implicit trust mechanisms underscore the need for industry-wide vigilance and immediate updates to firmware and software.

Future Outlook: Experts Weigh in on the Solution

Cybersecurity experts caution that addressing these flaws requires a multi-layered approach. Shu-Hao Tung emphasized in his presentation that network administrators must:

• Disable default VXLAN ‘Learning Mode’ configurations wherever possible.
• Enforce encryption for GRE and other tunneling protocols by default.
• Deploy robust intrusion detection systems (IDS) capable of recognizing spoofed traffic patterns.
• Harden routers and endpoints against NAT exploitation techniques.

David Scott, a penetration tester with 10 years of enterprise security experience, notes, “The risks exposed in this research are a wake-up call for companies relying on legacy protocols. While newer technologies like SD-WAN provide flexibility, misconfigurations at the protocol level can create cascading vulnerabilities that offset any benefits.”

Meanwhile, industry leaders are starting to take action. Reports indicate that MikroTik has already released a patch addressing VXLAN learning mode vulnerabilities in its RouterOS firmware, urging all users to update to the latest version. Similarly, organizations leveraging GRE-based networks are being advised to segment tunneling endpoints and limit exposure through strict firewall rules.

Are You Prepared for Tomorrow’s Threats?

Tung’s groundbreaking research not only sheds light on intrinsic weaknesses in widely used protocols but also serves as a cautionary note to the telecom and networking industries. As businesses increasingly rely on digitization and remote connectivity, securing the foundational protocols enabling these technologies is imperative.

What steps is your organization taking to secure its networking infrastructure? Share your thoughts and proactive measures in the comments below.