Correct Answer:

See The answer in Explanation part below.
Explanation:
Step 1 - Recognise this as a direct, high-stakes scope-boundary and safety issue. This is a serious situation: a legitimately in-scope system provides a technical path that could reach an explicitly, emphatically excluded system ("do not interact with under any circumstances") that the client itself believed was already isolated.
Proceeding with full exploitation of the in-scope web application without addressing this discovery first would create a genuine, material risk of inadvertently affecting the excluded fragile legacy system - precisely the outcome the exclusion was designed to prevent.
Step 2 - Pause before proceeding further on this specific path. Consistent with the syllabus principle on discovering unplanned pivot paths toward out-of-scope systems, your team should pause any further exploitation activity on the in-scope web application that could plausibly reach the shared backend database, rather than proceeding on the basis that the web application itself is technically in scope - the relevant risk here is the downstream reachability of the excluded system, not merely the starting point's scope status.
Step 3 - Escalate immediately and clearly to the Control Group. This discovery must be escalated promptly and clearly to the Control Group, explaining precisely what has been found: that the excluded legacy system is not, in fact, isolated as previously believed, and that a legitimately in-scope system provides a plausible technical path to it. This is exactly the kind of significant, safety-relevant scope discovery that requires an explicit Control Group risk decision before any further related activity proceeds, consistent with the syllabus's repeated emphasis on escalating rather than unilaterally resolving scope-boundary ambiguities, especially ones with genuine safety/fragility implications.
Step 4 - Present the Control Group with realistic options, not just a problem. You should help the Control Group understand the realistic options: (a) proceeding with carefully scoped, closely controlled activity that demonstrates the reachability risk without actually interacting with the excluded system's own data or functionality (e.g., demonstrating database-level access is achievable in principle, using a proof-of-concept approach analogous to the "create and remove a labelled test artefact" principle discussed elsewhere in this practice set, without ever querying or touching the legacy system's actual tables/data) - an approach that could deliver highly valuable risk insight while respecting the spirit of the exclusion; (b) excluding further technical demonstration of this specific path altogether and instead documenting the newly discovered reachability as a critical, urgent finding in its own right, given its significance; or (c) if the Control Group wishes to genuinely understand the full extent of exposure, formally and explicitly amending the exclusion (with appropriate additional risk controls and stakeholder sign-off, given the legacy system's described fragility) to permit carefully controlled, limited investigation - a significant decision that should not be made lightly or without input from whoever owns/understands the fragile legacy system best.
Step 5 - Treat the discovery itself as an urgent, high-value finding regardless of what testing path is chosen.
Independently of how (or whether) further technical demonstration proceeds, the fact that the client's own assumption about system isolation was incorrect is itself an extremely significant finding that should be communicated to the Control Group with urgency, given its potential relevance well beyond this engagement (e.g., to the client's own ongoing operational risk management, patching, and architecture decisions) - this is exactly the kind of urgent, severe finding that, per the reporting domain, should be escalated promptly rather than held until the final report.
Step 6 - Reflect on what this reveals about the client's own environment understanding, and note it explicitly. This discovery reveals a genuine, material gap between the client's assumed architecture (systems fully separated) and its actual, current-state architecture (a partially completed migration leaving a shared backend) - a gap the client's own IT team was unaware of until your team's reconnaissance surfaced it. This is valuable, standalone insight for the client about the reliability of its own architecture documentation and change-management assurance processes, and should be explicitly reflected in your reporting/closure commentary as a broader lesson, not just narrowly treated as a scoping technicality to be resolved and then forgotten.
Step 7 - Document the whole episode thoroughly. The discovery, the escalation, the Control Group's decision, and the rationale should all be clearly and contemporaneously documented, both to protect the integrity of the engagement's record and because this kind of significant, safety-relevant scope discovery is precisely the sort of event most likely to be scrutinised later if any question about the engagement's conduct ever arose.
Conclusion: Further exploitation activity on the path toward the excluded legacy system should pause immediately upon discovery, with prompt escalation to the Control Group presenting realistic options ranging from carefully controlled, non-intrusive demonstration to full exclusion of further technical activity on that path; the discovery itself should be treated and escalated as an urgent, high-value finding in its own right; and the episode should be explicitly used to highlight, in reporting, the client's own gap between assumed and actual system architecture as a valuable standalone lesson.
---