Zero-Harm Verification and Pre-Parser Interception for Deserialization, External Entities, and Template Injection
An attacker uploads an XML document with an external file reference, a serialized binary object containing a hidden command chain, or a template expression that executes code on the server. The verifier confirms parser susceptibility using inert mathematical tokens while blocking file and command execution on the wire.
Complex document parsers, object deserializers, and server-side template engines become high-severity execution vectors when untrusted input controls parser directives or object class instantiation. External entity declarations in XML allow arbitrary file disclosure and internal port scanning, native binary deserializers trigger gadget chains that invoke shell commands, and unescaped template strings grant direct access to runtime internals.
Security Officer (Plain Meaning): Halts "Execute remote gadget-chain subprocess, read /etc/shadow via XXE SYSTEM entity, or run SSTI os.popen" before socket (0 live DB damage, signed GOST receipt)
IT Auditor & SecOps (Evidence): Scope OWASP A08:2021 / A03:2021 | Wire Rule SEC-ZD-V2-05 | Formal Witness 9e53c184f6027d91
Technocrat, CTO & VC (Moat): Z3 Invariant (assert (and (= (xml_doctype_entity_decl body) false) (= (... | FP = 0.0% | Contract IMMUNE-DES-9E53C184 (mcp-sentinel 1.1.2)1. In-Path Interception and Contract Synthesis Schematic for WEB-DES-05
Deterministic verification flow for WEB-DES-05 (OWASP A08:2021 / A03:2021, CWE-502 / CWE-611 / CWE-1336): wire filter SEC-ZD-V2-05 intercepts destructive mutations prior to socket delivery, formal witness 9e53c184f6027d91 proves the flaw, and compiler emits gateway rule IMMUNE-DES-9E53C184 for mcp-sentinel.
2. Zero-Damage Wire Filtering and Formal Solver Invariant for WEB-DES-05
Under rule SEC-ZD-V2-05, the software wire filter intercepts any payload carrying destructive gadget classes, external network entity URLs, sensitive credential paths, or operating system execution calls before socket delivery.
On the benchmark stand, the verifier proves parser susceptibility using harmless local arithmetic expressions and inert entity markers compared against hardened parser configurations. The differential check records formal witness 9e53c184f6027d91 with zero false positives.
Class Identifier: WEB-DES-05 (deserialization_xxe_ssti)
Taxonomy Concordance: OWASP A08:2021 / A03:2021 | CWE-502 / CWE-611 / CWE-1336
Execution Mode: Active Safe Probing (AUTO_SCAN)
Candidate Probe: POST /api/v1/import/xml ]>&xxe;
Blocked Mutation: Execute remote gadget-chain subprocess, read /etc/shadow via XXE SYSTEM entity, or run SSTI os.popen
Z3 Solver Invariant: (assert (and (= (xml_doctype_entity_decl body) false) (= (object_gadget_magic_bytes body) false) (= (template_eval_directive body) false)))
Wire Sandbox Rule: SEC-ZD-V2-05
Formal Witness Hash: 9e53c184f6027d91
Compiled Sentinel Rule: IMMUNE-DES-9E53C184 (mcp-sentinel 1.1.2)3. Autonomous Synthesis of Gateway Contract IMMUNE-DES-9E53C184 and Streebog-256 Receipt
From witness 9e53c184f6027d91, the compiler synthesizes contract IMMUNE-DES-9E53C184 for border enforcement. The rule rejects document type declarations (DOCTYPE / ENTITY), blocks binary serialization magic headers, and strips template evaluation delimiters inside mcp-sentinel.
4. Engineering Reference Notes for WEB-DES-05
Proving template injection and XML entity expansion without executing shell commands
The verifier injects a deterministic arithmetic or local parameter reflection token and checks whether the server evaluates the expression, proving the parser flaw mathematically without invoking system binaries.
Eliminating deserialization gadget chains at the API proxy boundary
The compiled gateway contract rejects native binary object streams (such as Java serialized headers, Python Pickle, and PHP object tags) and enforces pure JSON schema validation.