Cross Domain Solutions for Zero Trust Data Sharing

Zero Trust has moved from policy language to procurement requirement across federal civilian agencies and defense components. But most Zero Trust discussions stop at identity, device posture, and micro-segmentation within a single enclave. The harder problem, one that does not get enough attention in architecture reviews, is what happens when mission requirements force data to cross between networks operating at different classification levels or different security domains.

That is where Cross Domain Solutions become central to Zero Trust implementation rather than peripheral to it. A Cross Domain Solution is not just a data transfer mechanism. In a properly designed Zero Trust architecture, it becomes an enforcement point, a filtering layer, and a policy boundary all at once. Understanding how those roles interact is what separates a defensible architecture from one that satisfies the checklist but fails during an actual mission exchange.

Federal environments are not clean. They carry legacy systems that were never designed for Zero Trust, network boundaries that exist because of physical infrastructure decisions made decades ago, and mission dependencies that cannot wait for a full modernization cycle. Practitioners need to understand how CDS fits into Zero Trust not as an abstract framework exercise, but as a concrete engineering and acquisition decision that affects operational risk, staffing, sustainment, and audit posture simultaneously.

This article addresses that directly. It is written for architects, engineers, ISSOs, and program managers who are being asked to make Zero Trust work in environments where secure data sharing between domains is not optional and where the architecture has to survive contact with real-world constraints.

What a Cross Domain Solution Actually Does in a Federal Environment

A Cross Domain Solution is a controlled interface that allows information to move between two or more security domains while enforcing policy at the boundary. That definition sounds simple. The operational reality is considerably more complex. CDS technology encompasses file transfer, messaging, video streaming, remote access, and web services filtering, and each use case carries its own set of engineering requirements, accreditation requirements, and operational risks.

In practice, most federal environments use CDS for one of three things: transferring files between classified and unclassified networks, enabling personnel to access services across enclaves without moving data through uncontrolled mechanisms, or supporting mission partner data exchange where the receiving domain is outside direct organizational control. Each of those scenarios introduces different risk profiles and different requirements for how the solution must be configured, monitored, and maintained.

The National Security Agency maintains the Raise the Bar initiative and the Cross Domain Solution approval process under the National Cross Domain Strategy and Management Office. Solutions evaluated through that process carry formal accreditation that matters to authorizing officials. But accreditation of the product itself is only the starting point. The system-level authorization, the connection approval, and the data transfer agreement layer on top of the product accreditation and represent the majority of the programmatic and compliance burden that practitioners actually live with.

What distinguishes a mature CDS deployment from a minimally compliant one is how deeply the organization has thought through content inspection policy, audit log retention, incident response procedures for policy violations, and the process for updating filtering rules when mission requirements change. Those operational elements are where most programs struggle, not the initial installation.

How Zero Trust Principles Map to CDS Architecture

Zero Trust is built on the premise that no user, device, or data flow should be trusted by default regardless of network location. That principle has a natural structural alignment with how Cross Domain Solutions are designed to operate. The challenge is that most Zero Trust frameworks were developed with intra-enclave and cloud scenarios as the primary reference architecture. The domain boundary case, where data must cross between systems that are physically and logically separated by design, requires specific architectural treatment that generic Zero Trust guidance does not fully address.

The core Zero Trust tenets defined in NIST SP 800-207 include verifying all entities explicitly, using least privilege access, and assuming breach. Each of those maps directly to CDS control functions when you trace the data flow at a domain boundary.

Explicit Verification at the Boundary

A CDS does not transfer data based on implied trust in the originating system. It inspects the data itself, validates it against policy, and makes an explicit permit or deny decision. This is analogous to what a policy decision point does in a Zero Trust model. The difference is that the CDS operates at the data level rather than the session or identity level, which is exactly what is needed at a classification boundary where the originating identity cannot be fully verified or trusted in the destination domain.

Architecturally, this means the CDS must be configured to understand what constitutes a valid data transfer for the specific use case it supports. A CDS processing imagery files behaves differently from one handling email or structured database records. The inspection logic needs to reflect actual mission data, not a generic policy template.

Least Privilege at the Data Flow Level

Zero Trust requires that access and data flow be scoped to the minimum necessary for the function being performed. At a domain boundary, this means the CDS should transfer only what is required for the receiving domain to complete its mission function. This sounds obvious, but in practice many organizations configure CDS solutions permissively at initial deployment and then leave the configuration static as mission requirements evolve. The result is a data transfer surface that expands over time without corresponding policy review.

Least privilege at the data flow level requires active governance. Filtering rules need periodic review against current mission requirements. Data types that were relevant two years ago may no longer justify the transfer risk today. Programs that treat CDS policy as a one-time configuration activity rather than an ongoing governance responsibility drift away from Zero Trust posture without realizing it.

Assume Breach and Audit Everything

The assume breach tenet drives logging and monitoring requirements that CDS solutions must fully support. Every transfer, every rejection, every policy exception needs to generate a log record that can be correlated with identity and session data from the broader Zero Trust architecture. This is where integration between CDS audit logging and SIEM platforms becomes operationally important. A CDS that generates detailed local logs but does not feed those records into the centralized monitoring environment creates blind spots that an adversary can exploit and that an inspector general will find.

Enabling Secure Collaboration Across Classification Boundaries

Secure collaboration across classification boundaries is one of the more operationally demanding requirements in federal IT. The mission need is clear: personnel working at different classification levels frequently need to share products, coordinate on time-sensitive decisions, or access shared reference data. The technical and policy machinery required to support that need safely is substantial.

The most common collaboration scenarios that drive CDS requirements include intelligence dissemination from higher to lower classification levels, coalition or mission partner data sharing where the partner operates on a different network, and operational data feeds that aggregate information from multiple classification levels for decision support. Each of these involves different data types, different latency tolerances, and different governance requirements for what can be released and under what conditions.

One area that frequently creates friction is the relationship between cross domain solutions and the data labeling and classification infrastructure that feeds them. A CDS inspection filter is only as effective as the labeling and tagging applied to the data being transferred. Organizations that have inconsistent or manual classification processes upstream of the CDS introduce risk at the boundary because the solution cannot reliably distinguish what should and should not transfer when the source data is improperly marked.

This is a systemic issue in many legacy environments. Data was created before structured metadata tagging was standard practice, classification markings live in document headers rather than machine-readable attributes, and the CDS must make transfer decisions based on file-level inspection rather than authoritative metadata. Modernization pressure has pushed many organizations toward automated data tagging and structured records management, but the transition is incomplete in most programs and the CDS must operate effectively during that transition period.

The collaboration use case also requires consideration of latency and workflow integration. Personnel who need to share data across domains should not face a workflow that requires submitting a transfer request to a manual review queue with a multi-hour turnaround if the mission requires near-real-time coordination. The architecture needs to balance security enforcement with operational tempo, and the policy and technical design of the CDS should reflect that balance explicitly rather than defaulting to maximum restriction without accounting for mission impact.

Implementation Friction, Staffing, and Sustainment Realities

Procurement and deployment of a CDS in a Zero Trust architecture involves friction that program offices routinely underestimate. The accreditation pipeline for NSA-approved Cross Domain Solutions is not a standard enterprise IT procurement process. Solutions that have gone through the formal evaluation process carry specific configuration requirements, documentation obligations, and operational restrictions that flow directly from the product evaluation. Deviating from those configurations to accommodate local integration requirements can invalidate the product accreditation, which then complicates the system-level authorization.

Timelines are a consistent pain point. Depending on the solution selected, the use case, and the accreditation path, organizations should expect the gap between decision to deploy and operational capability to be measured in months to years rather than weeks. That timeline needs to factor into Zero Trust roadmap planning. Programs that announce a Zero Trust target architecture with domain boundary enforcement as a core component but then discover the CDS acquisition process takes eighteen months are setting themselves up for either a delayed milestone or a gap in the intended architecture that persists while the procurement works through the system.

Staffing carries its own challenges. Operating a CDS correctly requires personnel who understand both the security domain requirements and the technical operation of the solution. That combination is not common in the general IT workforce. Many organizations find that the personnel who understand the classification guidance and the data transfer policy do not have deep technical background in the specific CDS platform, while the engineers who can manage the platform do not have sufficient security clearance or policy background to make informed decisions about filtering rules. Building a team that bridges both requires deliberate workforce planning rather than assuming it will work itself out during deployment.

Sustainment costs are also frequently underbudgeted. A CDS is not a set-and-forget appliance. Software updates, hardware refresh cycles, filter rule updates, connection approval renewals, and changes driven by mission requirement shifts all generate ongoing labor and procurement activity. Organizations that treated CDS procurement as a one-time capital expense and did not build recurring sustainment into the program budget find themselves operating end-of-life hardware, running outdated firmware, and carrying deferred maintenance that creates both security and compliance risk.

Integration with the broader Zero Trust architecture adds another layer of complexity. A CDS that generates detailed transfer logs but cannot export those logs in a format that the organization’s SIEM platform ingests creates monitoring gaps. The integration work required to bridge legacy CDS log formats with modern security analytics platforms is real engineering work that needs to be scoped, resourced, and tested. Treating it as a minor configuration task during deployment typically results in it being deferred until an audit or incident forces the issue.

Common Mistakes in Zero Trust CDS Deployments

The most damaging mistake organizations make is treating the CDS as a compliance artifact rather than an active security control. This happens when the focus of the deployment effort is the connection approval paperwork rather than the operational policy that the solution enforces. An organization can complete every required document, receive connection approval, and deploy a CDS that is technically operational but configured with permissive default rules, inadequate logging, and no defined process for reviewing transfer policy. That deployment satisfies the compliance requirement on paper while providing far less actual security than the architecture implies.

A second frequent mistake is decoupling the CDS from the broader Zero Trust identity and access management architecture. Zero Trust requires that data flows be tied to verified identities and authorized sessions, not just network paths. A CDS that accepts transfers from any system on the source network without reference to who initiated the transfer or whether that user has authorization for the specific data type is operating on implied network trust. That is precisely the model Zero Trust is designed to eliminate. Integrating CDS transfer decisions with identity attributes and session context is technically more complex, but it is necessary for the architecture to actually reflect Zero Trust principles rather than merely invoking the terminology.

Organizations also frequently underinvest in testing CDS filter rules against realistic mission data before going operational. Filter rules tested against synthetic data often behave differently when processing actual operational content. Complex file formats, embedded objects, metadata structures that vary across applications, and edge cases in data labeling can all cause unexpected policy outcomes. Mission-critical transfers that fail silently or generate false rejections create operational pressure to loosen policy, which over time erodes the security posture the CDS was deployed to enforce.

Redundancy and failover planning for CDS infrastructure is another area where programs routinely underinvest. A CDS that fails brings cross-domain data sharing to a halt. For missions that depend on that sharing, availability of the CDS is a mission readiness issue, not just a system availability issue. High availability configurations for accredited CDS solutions require specific planning because the redundancy architecture itself must maintain the security properties of the approved configuration. Improvised workarounds during CDS outages, such as using removable media to move data manually, introduce exactly the uncontrolled transfer risks the CDS was deployed to prevent.

Finally, programs often fail to account for how CDS requirements evolve as mission requirements shift. A solution accredited for a specific set of data types and transfer patterns may not accommodate a new mission function without configuration changes that require a return through the connection approval process. If the program office does not understand that dependency, they can commit to new mission capabilities without understanding that expanding the CDS scope requires additional authorization activity that will add months to the delivery timeline.

Recommended Federal Approach

Start with mission requirements, not product selection. The question that should drive CDS architecture is what data needs to move, between which domains, at what frequency, with what latency tolerance, and under what authorization constraints. Those requirements determine the CDS capability profile required. Starting with a specific product and working backward to justify it typically produces an architecture that fits the product’s capabilities rather than the mission’s requirements.

Engage the authorizing official and the program’s ISSM early and often. CDS deployments that proceed to procurement and installation before the AO is engaged on authorization approach and boundary definitions frequently encounter late-stage surprises that force expensive redesign. The AO and ISSM need to understand how the CDS fits into the system authorization boundary, what continuous monitoring requirements it generates, and how it interacts with existing security controls in the environment. Those conversations are much easier before hardware is on the floor than after.

Build the data classification and labeling infrastructure that the CDS depends on before deploying the solution. If the source environment does not produce consistently and accurately labeled data, the CDS cannot enforce policy reliably. Investments in structured metadata, automated classification tools, and consistent records management practices upstream of the CDS boundary pay direct dividends in the reliability and defensibility of the CDS enforcement function.

Plan for sustainment at the same level of rigor as initial deployment. Assign clear ownership for filter rule governance, establish a defined review cycle, and build the budget for hardware lifecycle, software maintenance, and workforce training into the program baseline. Organizations that treat CDS sustainment as an afterthought create program risk that surfaces at the worst possible time, typically during an audit, an operational stress event, or when a mission requirement changes and the program lacks the capacity to respond.

Integrate CDS logging with centralized security monitoring from the beginning. The value of a CDS in a Zero Trust architecture depends in part on the visibility it provides into data flows at domain boundaries. That visibility is only actionable if the logs feed into a monitoring environment where analysts can correlate them with identity, session, and endpoint data. Getting this integration right from the initial deployment avoids the common situation where the CDS generates data no one is actually reviewing.

For programs that are earlier in the planning cycle, the Anchor Defense resources library includes additional guidance on CDS architecture considerations and Zero Trust alignment that can support early planning decisions before formal requirements documentation is complete.

The organizations that get this right are not necessarily the ones with the largest budgets or the most sophisticated technology stacks. They are the ones that treat the CDS as a mission system in its own right, subject to the same lifecycle discipline, operational governance, and engineering rigor as any other system the mission depends on. That orientation produces architectures that hold up under operational pressure, satisfy validators during assessments, and adapt as mission requirements evolve, which is what Zero Trust in a real federal environment actually requires.