Axum 0.8 Hyper HTTP/3 Early Data 0-RTT Anti-Replay Guardrail

--- description: Axum 0.8 Hyper HTTP/3 Early Data 0-RTT Anti-Replay Guardrail - Enforces strict isolation and validation of QUIC 0-RTT early data within Axum 0.8 and Hyper HTTP/3 stacks. Non-idempotent HTTP methods and state-mutating handlers must reject early data with HTTP 425 (Too Early) or validate cryptographically bound TLS exporter tokens against replay windows to prevent replay-induced state corruption. globs: src/**/*.rs, crates/**/*.rs alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/axum-hyper-h3-early-data-anti-replay-guardrail" --- # Axum 0.8 Hyper HTTP/3 Early Data 0-RTT Anti-Replay Guardrail > **Severity**: CRITICAL | **Category**: backend > **Anti-Pattern Warning**: Executing state-mutating requests over unverified QUIC 0-RTT Early Data, enabling on-path packet replay attacks. ## System Constraints You are a Principal Systems & Security Architect enforcing zero-trust HTTP/3 protocol invariants in Rust using Axum 0.8 and Hyper. You must ensure that QUIC 0-RTT (Early Data) is never permitted to execute stateful, non-idempotent operations without explicit anti-replay defenses (RFC 8470 / RFC 9114). ## Strict Guidelines - Engineers MUST ALWAYS inspect incoming request protocol extensions to determine if an HTTP/3 request arrived via 0-RTT Early Data. - Engineers MUST NOT allow non-safe HTTP methods (POST, PUT, PATCH, DELETE) to execute in 0-RTT context without explicit idempotency keys and TLS exporter verification. - Services MUST respond with HTTP status code 425 Too Early whenever a state-mutating endpoint receives early data, forcing the client to retransmit after 1-RTT handshake finalization. - Components NEVER assume network-layer replay caches fully mitigate application-layer replays across distributed load-balanced Axum worker nodes. - Code SHOULD enforce tower-layer middleware that strips or rejects Early Data extensions upstream of business logic routers. ## Bad vs Good Implementations ### Tower Middleware Rejecting 0-RTT on Non-Idempotent Axum 0.8 Routes #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The handler processes state-altering financial logic directly. If served over HTTP/3 with 0-RTT enabled, an on-path attacker can record the initial QUIC flight and replay it multiple times against the server, leading to duplicate state changes. ```rust use axum::{routing::post, Router, Json}; use serde::Deserialize; #[derive(Deserialize)] struct TransferPayload { account_id: String, amount_cents: u64, } // VULNERABLE: Handles financial mutation without inspecting if the HTTP/3 request // arrived via QUIC 0-RTT Early Data. An attacker capturing the initial packet // can replay the raw 0-RTT datagram to cause duplicate transfers before the session expires. async fn transfer_funds(Json(payload): Json<TransferPayload>) -> &'static str { // Deduct and transfer funds directly println!("Transferring {} to {}", payload.amount_cents, payload.account_id); "Transfer completed" } pub fn app() -> Router { Router::new().route("/api/v1/transfers", post(transfer_funds)) } ``` #### Production Standard (Correct) > **Standard**: The middleware evaluates whether the request arrived via 0-RTT early data. For non-safe HTTP methods, it immediately responds with HTTP 425 Too Early and the Early-Data header, requiring the QUIC stack to finalize the cryptographic handshake before executing the request. ```rust use axum::{ body::Body, extract::Request, http::{Method, StatusCode}, middleware::{self, Next}, response::{IntoResponse, Response}, routing::post, Json, Router, }; use serde::Deserialize; #[derive(Clone, Copy, Debug)] pub struct IsEarlyData(pub bool); /// Middleware enforcing RFC 8470 / RFC 9114 0-RTT rejection for non-safe methods. pub async fn reject_early_data_middleware( req: Request<Body>, next: Next, ) -> Response { let is_early = req.extensions().get::<IsEarlyData>().is_some_and(|d| d.0); let is_safe = matches!(req.method(), &Method::GET | &Method::HEAD | &Method::OPTIONS); if is_early && !is_safe { // Return HTTP 425 Too Early to demand 1-RTT completion before processing. return ( StatusCode::TOO_EARLY, [("Early-Data", "1")], "Request rejected in 0-RTT window; retry after 1-RTT handshake", ) .into_response(); } next.run(req).await } #[derive(Deserialize)] struct TransferPayload { account_id: String, amount_cents: u64, } async fn transfer_funds(Json(payload): Json<TransferPayload>) -> &'static str { println!("Transferring {} to {}", payload.amount_cents, payload.account_id); "Transfer completed" } pub fn app() -> Router { Router::new() .route("/api/v1/transfers", post(transfer_funds)) .layer(middleware::from_fn(reject_early_data_middleware)) } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Axum 0.8 Hyper HTTP/3 Early Data 0-RTT Anti-Replay Guardrail

Axum 0.8 Hyper HTTP/3 Early Data 0-RTT Anti-Replay Guardrail defines an industrial-grade behavioral standard for backend engineering. Enforces strict isolation and validation of QUIC 0-RTT early data within Axum 0.8 and Hyper HTTP/3 stacks. Non-idempotent HTTP methods and state-mutating handlers must reject early data with HTTP 425 (Too Early) or validate cryptographically bound TLS exporter tokens against replay windows to prevent replay-induced state corruption. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Executing state-mutating requests over unverified QUIC 0-RTT Early Data, enabling on-path packet replay attacks. Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Executing state-mutating requests over unverified QUIC 0-RTT Early Data, enabling on-path packet replay attacks.	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS inspect incoming request protocol extensions to determine if an HTTP/3 request arrived via 0-RTT Early Data.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.