T1599 - Network Boundary Bridging

Adversaries may bridge network boundaries by compromising perimeter network devices or internal devices responsible for network segmentation. Breaching these devices may enable an adversary to bypass restrictions on traffic routing that otherwise separate trusted and untrusted networks.

Devices such as routers and firewalls can be used to create boundaries between trusted and untrusted networks. They achieve this by restricting traffic types to enforce organizational policy in an attempt to reduce the risk inherent in such connections. Restriction of traffic can be achieved by prohibiting IP addresses, layer 4 protocol ports, or through deep packet inspection to identify applications. To participate with the rest of the network, these devices can be directly addressable or transparent, but their mode of operation has no bearing on how the adversary can bypass them when compromised.

When an adversary takes control of such a boundary device, they can bypass its policy enforcement to pass normally prohibited traffic across the trust boundary between the two separated networks without hinderance. By achieving sufficient rights on the device, an adversary can reconfigure the device to allow the traffic they want, allowing them to then further achieve goals such as command and control via Multi-hop Proxy or exfiltration of data via Traffic Duplication. Adversaries may also target internal devices responsible for network segmentation and abuse these in conjunction with Internal Proxy to achieve the same goals.(Citation: Kaspersky ThreatNeedle Feb 2021) In the cases where a border device separates two separate organizations, the adversary can also facilitate lateral movement into new victim environments.

Atomic Tests:

Currently, no tests are available for this technique.

Detection

Consider monitoring network traffic on both interfaces of border network devices with out-of-band packet capture or network flow data, using a different device than the one in question. Look for traffic that should be prohibited by the intended network traffic policy enforcement for the border network device.

Monitor the border network device’s configuration to validate that the policy enforcement sections are what was intended. Look for rules that are less restrictive, or that allow specific traffic types that were not previously authorized.

Shield Active Defense

Security Controls

Alter security controls to make the system more or less vulnerable to attack.

Manipulating security controls involves making configuration changes to the security settings of a system including things like modifying Group Policies, disabling/enabling autorun for removable media, and tightening or relaxing system firewalls, etc.

Opportunity

There is an opportunity to use security controls to stop or allow an adversary’s activity.

Use Case

In an adversary engagement scenario, a defender can implement weak security controls that an adversary could subvert in order to further their attack.

Procedures

Weaken security controls on a system to allow for leaking of credentials via network connection poisoning. Implement policies on a system to prevent the insecure storage of passwords in the registry. This may force an adversary to revert these changes or find another way to access cached credentials.