Cross Domain Solution Red Teaming and Adversary Emulation: Validating Release Controls Against Realistic Attack Paths

Cross domain solution red teaming is one of the least standardized and most consequential validation activities a federal program can undertake. Most organizations treat CDS security testing as a compliance artifact, something to produce for the authorization package and file away. That approach leaves real attack paths unexamined and gives authorizing officials a false picture of what the solution actually blocks.

A CDS is not a conventional IT system. It enforces release controls between security domains at the boundary where the consequences of failure are highest. The guard logic, filter chains, content inspection engines, and policy enforcement points inside a CDS are purpose-built to prevent unauthorized data transfer. But purpose-built does not mean infallible. Policy configurations drift. Content inspection has edge cases. Operators make decisions under time pressure. Malformed payloads behave differently than clean test files. None of that shows up in a standard vulnerability scan or a checklist-based security assessment.

Red teaming changes the question from “does the system have known vulnerabilities?” to “can an adversary move data across this boundary in ways the policy is supposed to prevent?” That is a fundamentally different test. It requires structured adversary emulation, mission-specific attack scenarios, and a disciplined process for capturing evidence, triaging findings, and feeding results back into both remediation and the authorization package.

This article is written for teams that are implementing or hardening a CDS and need a practical framework for conducting adversarial validation before authorization and during operations. It covers threat modeling, scope and rules of engagement, attack-path design, evidence collection, findings taxonomy, remediation verification, and how results connect to the broader authorization and lifecycle process.

Threat Modeling for CDS Adversaries

Before any test case is written, the team needs a working threat model specific to the CDS deployment. Generic threat models built for enterprise IT do not map cleanly to cross-domain boundary enforcement. The attack surface is different, the failure modes are different, and the adversary objectives are different.

A CDS adversary is not primarily trying to compromise the guard appliance itself. The objective is to move data across the boundary in a way the policy prohibits, or to prevent legitimate transfers in a way that degrades mission operations. Those two objectives drive very different attack paths. Data exfiltration attempts exploit filter gaps, content inspection edge cases, and policy misconfiguration. Denial-of-service or disruption attempts exploit fail-safe behavior, queue management, and error handling.

Insider threat scenarios deserve specific attention. A CDS sits at a boundary that authorized users interact with regularly. An operator who understands the transfer workflow can craft submissions designed to exploit known filter tolerances, manipulate metadata to satisfy policy checks, or use legitimate file formats in ways the content inspection engine does not fully parse. These scenarios are not hypothetical. They reflect realistic misuse by personnel with authorized access and operational knowledge of the system.

The threat model should identify the data types the CDS is authorized to transfer, the domains it connects, the operator roles that interact with it, the downstream systems that consume transferred content, and the policy rules that govern each transfer path. Each of those elements represents a potential attack surface. The red team uses the threat model to prioritize which attack paths to develop first and which scenarios carry the highest mission consequence if they succeed.

Scope, Rules of Engagement, and Test Authorization

CDS red teaming requires more careful scoping than most other security test activities. The system sits between classified domains. Test actions that succeed, even partially, may result in actual data movement across a boundary, logging events that trigger incident response, or disruption to mission-critical transfer workflows. None of that is acceptable without explicit pre-authorization from the right stakeholders.

Stakeholder Coordination Before Testing

The system owner, ISSO, ISSM, mission operators, and a representative from the authorizing official’s office all need to be part of the scoping conversation before a test plan is finalized. This is not a courtesy. It is a requirement. The ISSO needs to understand what test actions will be attempted so that legitimate red team activity is not confused with an actual incident. Mission operators need to know which transfer workflows may be affected and during what windows. The authorizing official’s representative needs to understand how the test results will be used in the authorization package.

The rules of engagement document should specify the test environment, whether testing occurs on a production system or a representative test instance, the data classification levels involved, which attack categories are in scope, which are explicitly out of scope, the communication protocol if a test action produces an unexpected result, and the process for halting testing if a real incident is suspected. That last point matters. Red team exercises on CDS infrastructure can generate log events that look identical to real attacks. The incident response team needs a clear mechanism to distinguish test activity from genuine threats.

Test Environment Considerations

Testing on a production CDS is high-risk. A preferred approach is a representative test instance that mirrors the production configuration, including the same policy rules, filter settings, content inspection profiles, and network topology. The test instance should be validated against the production configuration before testing begins. Any drift between the two environments reduces the validity of the test results. If a representative environment is not available and production testing is required, the scope of active exploitation attempts should be significantly constrained and the test windows should be coordinated with operations to minimize mission impact.

Building the Attack-Path Catalog

The attack-path catalog is the operational core of the red team exercise. It translates the threat model into specific test cases that the red team executes against the CDS. Each entry in the catalog should identify the attack category, the specific technique, the expected system response, the observable evidence if the technique succeeds or fails, and the mission consequence of a successful bypass.

The following categories represent the primary attack surfaces for CDS adversarial testing. They are not exhaustive, but they cover the areas where real bypass paths have been identified in operational CDS deployments.

Policy bypass through configuration abuse. CDS policy rules are complex. They govern file types, data labels, transfer directions, user roles, and content attributes. Misconfigurations create gaps where transfers that should be blocked are permitted. Test cases in this category submit content that exploits ambiguous policy rules, uses file type combinations that the policy does not explicitly address, or presents label attributes in formats the policy engine parses differently than expected.

Content-based exploits and malformed payloads. Content inspection engines parse file content to enforce policy. Malformed files, files with embedded objects, files that exploit parser edge cases, and files that use legitimate format features in unexpected ways can produce inspection results that do not reflect the actual content. Test cases in this category submit files designed to stress the inspection engine, including documents with nested structures, files with corrupted headers that still parse, polyglot files that satisfy multiple format signatures, and files with content encoded in ways the inspection engine may not fully decode before making a policy decision.

Covert channel attempts. Covert channels exploit legitimate transfer mechanisms to move information that the policy does not explicitly govern. Common examples include encoding data in file metadata, using timing patterns in transfer requests, exploiting whitespace or formatting in permitted file types, and embedding data in image or document properties that the inspection engine does not strip. Content disarm and reconstruction processes are specifically designed to address many of these, but CDR implementations vary in coverage and depth.

Metadata manipulation. Files carry metadata that CDS policy engines may use to make transfer decisions. Manipulating metadata to present false classification markings, false originator information, or false file type signatures can affect policy outcomes. Test cases in this category examine how the CDS handles metadata that conflicts with file content, metadata that is absent, and metadata that has been modified after initial submission.

Operator error and workflow abuse. Operators interact with the CDS through submission interfaces, approval workflows, and exception processes. Test cases in this category simulate operator behaviors that could result in unauthorized transfers, including submitting content through exception workflows without appropriate justification, exploiting approval queue timing, and using legitimate operator privileges in sequences the policy was not designed to anticipate.

Fail-safe and error-handling behavior. What happens when the CDS encounters a file it cannot parse, a network interruption during transfer, or a policy engine error? Fail-safe behavior should default to blocking the transfer. Test cases in this category deliberately trigger error conditions to verify that the system fails closed rather than open.

Attack Category	Primary Target	Detection Difficulty	Mission Consequence if Successful
Policy configuration abuse	Policy rule gaps	Low to moderate	Unauthorized data release
Malformed payload submission	Content inspection engine	Moderate to high	Filter bypass, data exfiltration
Covert channel exploitation	CDR and metadata stripping	High	Low-bandwidth data leakage
Metadata manipulation	Policy decision inputs	Moderate	Incorrect policy outcome
Operator workflow abuse	Exception and approval processes	Low	Authorized-path misuse
Fail-safe and error handling	Error recovery logic	Low	Transfer permitted during fault condition

Evidence Collection and Logging Requirements

Evidence collection during CDS red teaming serves two distinct purposes. The first is operational: the red team needs to demonstrate what happened, what the system did in response, and whether the test objective was achieved. The second is programmatic: the evidence package needs to support both remediation tracking and the authorization body of evidence. Treating these as separate deliverables doubles the documentation burden and usually results in gaps in both.

Before testing begins, confirm that the CDS logging configuration captures the events the red team needs. This sounds obvious, but CDS logging configurations are frequently set to capture transfer outcomes without capturing the content attributes or policy decision details that explain why a transfer was permitted or blocked. If the logging configuration does not capture policy decision context, the red team cannot distinguish between a transfer that was blocked by the correct rule and a transfer that was blocked by an unrelated rule that happened to fire first.

The evidence package for each test case should include the test case identifier, the attack technique used, the payload or submission details, the system response, the relevant log entries with timestamps, a screenshot or capture of the transfer outcome where applicable, and the red team’s assessment of whether the test objective was achieved. For test cases where the system blocked the transfer, the evidence should confirm which control blocked it and whether that control was the intended one.

Log integrity matters. Red team log entries should be time-synchronized with the CDS system logs so that test actions can be correlated with system responses without ambiguity. If the CDS feeds a SIEM, confirm that the SIEM is capturing the relevant event types before testing begins. Post-test log review is significantly harder when log collection gaps are discovered after the exercise.

Findings Taxonomy and Remediation Verification

CDS red team findings do not map cleanly to standard vulnerability severity ratings. A finding that scores as medium severity using a generic framework may carry critical mission risk in a CDS context if it represents a viable path to unauthorized data release across a classified boundary. The findings taxonomy needs to reflect CDS-specific risk dimensions.

A practical taxonomy for CDS red team findings uses four dimensions: technical severity, exploitability under realistic conditions, mission consequence if exploited, and remediation complexity. Technical severity alone is insufficient. A finding that requires physical access to the guard appliance and specialized hardware has low exploitability even if the technical impact is high. A finding that any authorized operator can trigger through normal workflow interactions has high exploitability even if the technical mechanism is simple.

Findings should be categorized into three operational tiers. The first tier covers confirmed bypass paths where the red team successfully moved data or demonstrated a policy outcome that the system should have prevented. These require immediate remediation before authorization proceeds. The second tier covers partial bypasses or conditions where a bypass is theoretically possible but requires specific preconditions that reduce realistic exploitability. These require remediation with a defined timeline and compensating controls in the interim. The third tier covers configuration weaknesses, logging gaps, or operator workflow vulnerabilities that do not represent direct bypass paths but increase the attack surface. These feed into the plan of action and milestones and the ongoing configuration management process.

Remediation verification is a separate test activity, not a paper review. When a finding is remediated, the red team should re-execute the specific test case that produced the finding to confirm the fix is effective. Configuration changes that address one bypass path sometimes introduce new gaps. Re-testing after remediation is the only way to confirm the fix works as intended without creating a new problem.

The findings report should be structured to serve both the technical team and the authorization process. Technical staff need the full detail of each finding, including the technique, the payload, the log evidence, and the recommended fix. The authorizing official’s representative needs a summary that maps findings to risk tiers, identifies which findings were remediated before authorization, which are addressed through compensating controls, and which remain open with accepted risk. These are different documents with different audiences, and trying to serve both audiences with a single report usually serves neither well.

For programs implementing or hardening a Cross Domain Solutions (CDS) environment, the red team findings package becomes a durable artifact that supports not just the initial authorization but ongoing configuration reviews, periodic reassessments, and future red team exercises that test whether previously identified gaps remain closed.

Common Mistakes

Treating the red team exercise as a compliance checkbox. The most common failure mode is scoping the exercise to produce a report that satisfies an authorization requirement rather than to find real bypass paths. When the objective is documentation rather than discovery, the test cases are designed to pass, the scope excludes anything that might produce an uncomfortable finding, and the resulting report provides false assurance. An authorization package built on a compliance-oriented red team exercise does not reflect the actual security posture of the CDS.

Using generic penetration testing methodology without CDS-specific adaptation. Standard penetration testing frameworks are built around network and application attack surfaces. They do not include test cases for content inspection bypass, CDR evasion, policy configuration abuse, or cross-domain covert channels. A red team that applies a generic methodology to a CDS will miss the attack categories that are most relevant to the system’s actual function.

Failing to validate the test environment against production configuration. Testing on a representative environment that has drifted from the production configuration produces findings that may not apply to the production system and may miss gaps that exist in production but not in the test instance. Configuration drift between test and production environments is common and often undocumented. Validating the two configurations before testing begins is not optional.

Skipping operator workflow scenarios. Red teams with a technical focus tend to concentrate on content-based attacks and policy configuration abuse. Operator workflow scenarios require understanding how the system is actually used, which requires coordination with mission operators. That coordination takes time and is frequently skipped. The result is a red team exercise that tests the technology but not the human-system interaction, which is where many real bypass paths exist.

Not confirming logging coverage before testing. Discovering after the exercise that the CDS logging configuration did not capture the events needed to reconstruct test outcomes means the evidence package is incomplete. Remediation recommendations lack supporting evidence. Re-testing requires repeating the entire exercise. Confirming logging coverage is a pre-test requirement, not a post-test discovery.

Treating remediation as complete without re-testing. Configuration changes made in response to red team findings are frequently not re-tested. The program office marks the finding as closed based on a change ticket or a developer’s confirmation that the fix was applied. Without re-executing the test case, there is no evidence that the fix works as intended or that it did not introduce a new gap. Remediation verification through re-testing is the only reliable closure mechanism.

Not planning for periodic revalidation. CDS configurations change. Policy rules are updated. New data types are added to the transfer workflow. Software updates modify filter behavior. Each of these changes can affect the security posture in ways that the initial red team exercise did not anticipate. Treating the red team exercise as a one-time activity rather than a recurring validation function means the authorization is based on a snapshot that becomes less accurate over time.

Recommended Federal Approach

The following approach is structured for federal and defense programs that are implementing or hardening a CDS and need to conduct adversarial validation before authorization and during operations. It is not a universal checklist. Adjust the sequence and depth based on the program’s authorization timeline, available resources, and the operational maturity of the CDS deployment.

Phase 1: Threat model and scope definition. Begin with a structured threat modeling session that includes the system owner, ISSO, ISSM, and at least one mission operator who understands the transfer workflows. Document the data types, domains, operator roles, and policy rules that define the CDS attack surface. Use the threat model to prioritize attack categories for the initial exercise. Not every category needs to be tested in the first exercise. Prioritize the categories with the highest mission consequence and the most realistic exploitability given the threat environment.

Phase 2: Rules of engagement and test authorization. Draft the rules of engagement document and circulate it to all required stakeholders before any test planning proceeds. Resolve authority ambiguities at this stage. Confirm the test environment, the communication protocol for unexpected events, and the process for halting testing. Obtain written authorization from the system owner and the authorizing official’s representative before the test plan is finalized.

Phase 3: Test environment validation. Validate the test environment against the production configuration. Document any differences and assess whether those differences affect the validity of the planned test cases. If the differences are material, either resolve them before testing or document the limitations they impose on the findings.

Phase 4: Logging and evidence infrastructure. Confirm that the CDS logging configuration captures the event types needed to reconstruct test outcomes. Verify time synchronization between the red team’s logging and the CDS system logs. If the CDS feeds a SIEM, confirm that the relevant event types are being collected. Document the logging configuration as part of the pre-test record.

Phase 5: Test execution. Execute the attack-path catalog in the sequence defined by the test plan. Capture evidence for each test case using the standardized evidence package format. Document both successful bypasses and confirmed blocks. For confirmed blocks, record which control produced the outcome. Do not skip test cases because they are expected to fail. Unexpected results in either direction are the most valuable findings.

Phase 6: Findings triage and reporting. Triage findings using the four-dimension taxonomy: technical severity, exploitability, mission consequence, and remediation complexity. Produce a technical findings report for the engineering and operations team and a summary findings report for the authorization process. Identify which findings require remediation before authorization, which are addressed through compensating controls, and which are accepted risks with documented rationale.

Phase 7: Remediation verification. Re-execute test cases for all findings that were remediated. Document the re-test results as a separate evidence package that references the original finding. Update the findings report to reflect remediation status. Do not close a finding without re-test evidence.

Phase 8: Authorization integration and lifecycle planning. Incorporate the red team findings package, evidence packages, and remediation verification records into the authorization body of evidence. Establish a schedule for periodic revalidation based on the CDS change management process. Define the triggers that require an unscheduled red team exercise, including significant policy changes, software updates that affect filter or inspection behavior, and changes to the data types or domains the CDS serves. Build the revalidation schedule into the program’s lifecycle sustainment plan so it is funded and resourced, not treated as an ad hoc activity when the next authorization renewal approaches.