GRE Flood DDoS Attack

What is a GRE Flood DDoS Attack?

A GRE Flood is a specific form of Denial-of-Service (DoS) or Distributed Denial-of-Service (DDoS) attack in which large volumes of GRE packets (Generic Routing Encapsulation) are sent to a target system or network. The goal of the attack is to overload the bandwidth as well as the routing and processing capacities of the victim. GRE is a tunneling protocol that is actually used to build VPNs or connect separate networks. However, attackers abuse GRE to generate massive traffic outside classic TCP/UDP flows, which is not inspected by many firewalls and filters by default. This allows them to bypass protection mechanisms and specifically exhaust resources at the network and application level.

How does a GRE Flood DDoS Attack work?

In a GRE Flood, the attacker sends a large number of manipulated GRE packets with high bandwidth to the target. Since GRE traffic is frequently used for legitimate applications, it is difficult for many systems to distinguish malicious from legitimate GRE packets. Unlike classic attacks that use specific ports (as with TCP or UDP), the GRE Flood bypasses many filtering mechanisms by using the GRE protocol (IP protocol 47) at the IP level. Attackers mostly use botnets or open servers and additionally disguise the origin through IP spoofing.

• The attacker generates a large amount of GRE packets and sends them directly to the target network or target server.
• Since GRE is not bound to ports, conventional security rules on firewalls and routers are often bypassed.
• The target must process the incoming GRE packets, which can lead to overloading of bandwidth, CPU and ultimately a complete failure of the network connection.

The targeted overloading with GRE traffic can cause significant performance degradation or even failures in infrastructure components such as routers or firewalls, especially if these devices are not prepared for inspecting or filtering GRE. This makes GRE Floods a particularly effective method for attackers to bypass protection mechanisms and disrupt critical networks or services.

The 3 most common types of GRE Flood Attacks

• 1. Distributed GRE Flood (DDoS)

  In a Distributed GRE Flood, attackers combine the resources of numerous compromised systems or botnets to direct enormous volumes of GRE packets simultaneously against a target. Tracing the attack origins is thereby almost impossible and the attack potential is extremely high, since many ISPs do not block or monitor GRE traffic by default.

• 2. Direct GRE Flood

  Here, a single attacker or a small network specifically sends many GRE packets to the target. If the source IP is not spoofed, such an attack can be detected relatively easily, but often remains effective when the victim's infrastructure allows GRE traffic and no specific filters are in place.

• 3. GRE Flood with IP Spoofing

  IP spoofing means that the attacker manipulates the source IP addresses of the GRE packets. This makes it difficult to determine the attack origin and complicates defense measures. Often thousands of spoofing addresses are used so that blacklisting strategies do not work.

GRE Floods can have an enormous impact with comparatively little resource expenditure on the attacker's side, especially because the network stack of many systems is not designed for high GRE traffic and protection solutions do not always cover this protocol. As a result, even large IT infrastructures can be temporarily paralyzed by targeted GRE Flood attacks.

How to protect against a GRE Flood DDoS Attack?

To protect against GRE Flood DDoS attacks, various measures are recommended:

• Filter Rules for GRE Protocol (IP 47)

  Enable explicit rules in firewalls and routers to allow GRE traffic only between authorized endpoints. GRE traffic that is not needed should be blocked at the network perimeter.

• Deep Packet Inspection (DPI)

  Deploy systems that inspect GRE packets through DPI and detect unusual patterns (e.g. high packet frequency or deep nesting). This allows DDoS patterns to be detected and blocked early even in GRE tunnels.

• Rate Limiting for GRE

  Limit the permitted number of incoming GRE packets per time interval at your network boundaries. Many professional network devices offer special rate-limiting mechanisms for protocol 47 (GRE).

• Monitoring and Anomaly Detection

  Continuous network monitoring helps to immediately detect unusual volumes of GRE traffic and automatically initiate countermeasures.

How Tievolu protects your network against GRE Flood DDoS attacks

Tievolu PYRUS DDoS Protection

With "Tievolu PYRUS" DDoS Protection, our system detects and blocks attacks at the protocol level, including GRE Floods. Transitions and packets at all important protocol levels, incl. IP 47, are continuously analyzed and filtered in real time in the event of an attack. Our AI-powered systems detect unusual traffic patterns (such as sudden GRE frequencies) early and automatically install blocking or limiting rules. This reliably defends against non-standard attacks like GRE Floods without affecting legitimate applications.

Tievolu Cloud Firewall

With the Tievolu Cloud Firewall you can create explicit GRE filters, configure specific traffic limits and ensure that only authorized GRE peerings are possible. Combine this with further mechanisms such as geo-blocking or ASN filtering to further reduce the possible attack vector.