Deterministic Verification of Token Forgery, Algorithm Confusion, and OAuth 2.0 Redirect Flaws
An attacker alters the header of a session token to disable signature checking or tricks the login service into sending an authorization code to an external address. The verifier tests cryptographic signature enforcement on synthetic tokens, blocks outbound key-fetching calls on the wire, and compiles a strict token-validation contract for border enforcement.
Authentication failures in modern programming interfaces frequently stem from flawed validation of signed session tokens and federated authorization redirects. Common defects include accepting unsigned tokens via the none algorithm header, verifying symmetric signatures with public RSA key bytes, trusting unpinned key-set addresses in header fields, and permitting open redirect parameters during authorization code exchange.
Security Officer (Plain Meaning): Halts "Forge unsigned alg:none token, inject external jku key URL, or downgrade RS256 to HS256 using public key bytes" before socket (0 live DB damage, signed GOST receipt)
IT Auditor & SecOps (Evidence): Scope OWASP API2:2023 / WSTG-ATHN-10 | Wire Rule SEC-ZD-V2-01 | Formal Witness 7a14f903e2c81b52
Technocrat, CTO & VC (Moat): Z3 Invariant (assert (and (= (jwt_alg token) RS256_OR_GOST3410) (valid_... | FP = 0.0% | Contract IMMUNE-JWT-7A14F903 (mcp-sentinel 1.1.2)1. In-Path Interception and Contract Synthesis Schematic for API-JWT-01
Deterministic verification flow for API-JWT-01 (OWASP API2:2023 / WSTG-ATHN-10, MITRE T1550.001 / CWE-347): wire filter SEC-ZD-V2-01 intercepts destructive mutations prior to socket delivery, formal witness 7a14f903e2c81b52 proves the flaw, and compiler emits gateway rule IMMUNE-JWT-7A14F903 for mcp-sentinel.
2. Zero-Damage Wire Filtering and Formal Solver Invariant for API-JWT-01
Under rule SEC-ZD-V2-01, the in-path software filter restricts authentication testing to synthetic testbed principals and intercepts any outbound request triggered by header key pointers before a socket opens. Attempts to revoke live user sessions, overwrite identity provider keys, or forward tokens to external domains are halted inside the verifier.
On the benchmark stand, the verifier compares target responses to mutated token headers against a hardened reference handler that enforces pinned asymmetric algorithms and strict redirect matching. The differential check records formal witness 7a14f903e2c81b52 with zero false positives across compliant authentication gateways.
Class Identifier: API-JWT-01 (jwt_oauth_auth_bypass)
Taxonomy Concordance: OWASP API2:2023 / WSTG-ATHN-10 | MITRE T1550.001 / CWE-347
Execution Mode: Active Safe Probing (AUTO_SCAN)
Candidate Probe: GET /api/v1/profile Authorization: Bearer eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJzdWIiOiJhZG1pbiIsInJvbGUiOiJzdXBlcnVzZXIifQ.
Blocked Mutation: Forge unsigned alg:none token, inject external jku key URL, or downgrade RS256 to HS256 using public key bytes
Z3 Solver Invariant: (assert (and (= (jwt_alg token) RS256_OR_GOST3410) (valid_sig token pinned_jwk) (= (iss token) trusted_iss) (> (exp token) now)))
Wire Sandbox Rule: SEC-ZD-V2-01
Formal Witness Hash: 7a14f903e2c81b52
Compiled Sentinel Rule: IMMUNE-JWT-7A14F903 (mcp-sentinel 1.1.2)3. Autonomous Synthesis of Gateway Contract IMMUNE-JWT-7A14F903 and Streebog-256 Receipt
From witness 7a14f903e2c81b52, the compiler emits contract IMMUNE-JWT-7A14F903 for the perimeter proxy. The rule enforces explicit algorithm allowlisting, blocks dynamic remote key headers, and validates issuer, audience, and cryptographic signature claims in process memory inside mcp-sentinel.
4. Engineering Reference Notes for API-JWT-01
Prevention of asymmetric-to-symmetric algorithm confusion at the gateway
The gateway binds each verification key to a single cryptographic algorithm identifier in its configuration table, rejecting any token whose header declares a symmetric hash when the server key is an asymmetric public certificate.
Securing OAuth 2.0 authorization code flows against redirect interception
The compiled contract requires exact byte-for-byte equality on registered redirect addresses and mandates Proof Key for Code Exchange (PKCE) verification on every token exchange request.