Comparing parser handoff decisions without building an exploit payload

Goal

Test whether successive components agree on the security-relevant meaning of a benign request fixture. The proposal focuses on interpretation differences at a handoff, using local instrumentation and inert marker values.

Prerequisites

Use an isolated processing chain whose components can report their parsed representation. Select a harmless field that influences a test authorization or routing decision, and document which component owns normalization.

Steps

1. Create an unambiguous baseline fixture and capture the field as interpreted at every stage. Verify that instrumentation observes the actual decision input rather than a separately reconstructed display value.

2. Build bounded variants using harmless differences supported by the fixture format, such as repeated keys or surrounding whitespace. Specify the intended rejection or canonical interpretation before execution.

3. Compare parsed values, selected route, and authorization input across stages. Treat a disagreement as a hypothesis requiring trace evidence, rather than labeling every textual difference a vulnerability.

4. When a variant is ambiguous under the application contract, choose an explicit rejection rule or a single normalization boundary. Preserve the original fixture as a named regression input.

5. Rerun the baseline and variants after the change. Confirm that the final application decision uses the same representation that the enforcing component actually checked.

Expected result

The useful artifact is a compact table connecting fixture, stage, interpreted value, and final decision. It makes a boundary disagreement reviewable without relying on a destructive demonstration.

Limits and test basis

This method does not provide protocol-specific attack sequences or assert parser behavior for any named library. Production intermediaries and different versions need their own authorized fixtures. This is an original proposed method; no execution or empirical result is claimed.