Api Abuse in Axum

API abuse in Axum commonly manifests as Broken Object Level Authorization (BOLA) and Broken Function Level Authorization (BFLA). BOLA occurs when an endpoint uses user-supplied input (like a path parameter) to fetch an object without verifying that the user owns it. BFLA happens when a handler does not check the user's role before performing an action. These vulnerabilities rank among the most critical in the OWASP API Top 10, with BOLA listed as the #1 risk.

For example, this vulnerable handler returns a user profile based on the user_id path parameter without any authorization check:

async fn get_user_profile(Path(user_id): Path<u32>, State(state): State<Arc<AppState>>) -> impl IntoResponse { let profile = state.db.get_profile(user_id).await.unwrap(); Json(profile) }

An attacker can access any user's data by changing the user_id. Similarly, this deletion handler only verifies authentication, not role:

async fn delete_user(Path(user_id): Path<u32>, auth_user: AuthenticatedUser, State(state): State<Arc<AppState>>) -> impl IntoResponse { state.db.delete_user(user_id).await.unwrap(); StatusCode::NO_CONTENT }

Any authenticated user can delete arbitrary accounts. These flaws can lead to data breaches, account takeover, and privilege escalation. Other abuse patterns include missing rate limiting, input validation failures, and mass assignment. Axum's extractors parse data but do not enforce security; developers must implement checks manually.

Detect API abuse by scanning your Axum API with middleBrick. This black-box scanner sends crafted requests to test for unauthenticated access, IDOR, BFLA, and more. For a GET /api/users/{id} endpoint, it will try accessing it without credentials, with a low-privilege token to access other users' data, and with a regular user token to access admin-only functions.

middleBrick runs 12 security checks in parallel, including BOLA/IDOR, BFLA, Input Validation, and Rate Limiting. Scans take 5–15 seconds and return a risk score (0–100) with detailed findings and remediation guidance. Findings map to compliance frameworks (OWASP API Top 10, PCI-DSS, SOC2, HIPAA, GDPR). If you have an OpenAPI spec, middleBrick correlates it with runtime results for better accuracy. Additionally, middleBrick includes unique checks for LLM/AI security, such as prompt injection and system prompt leakage, making it valuable for modern APIs that integrate AI models.

Integrate middleBrick into your workflow via the CLI, GitHub Action, or MCP Server to catch abuse vulnerabilities early. Re-scan after fixes to verify improvements and track scores over time in the dashboard.

Fix API abuse in Axum using middleware and extractors.

Authentication: Create an extractor that validates credentials and returns a user object. Example using JWT:

struct AuthenticatedUser { id: u32, role: String, } #[async_trait] impl<S> FromRequestParts<S> for AuthenticatedUser where S: Send + Sync, { type Rejection = (StatusCode, &'static str); async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> { let token = parts.headers.get("Authorization") .ok_or((StatusCode::UNAUTHORIZED, "Missing token"))? .to_str().map_err(|_| (StatusCode::UNAUTHORIZED, "Invalid token"))?; let claims = validate_jwt(token).await.map_err(|_| (StatusCode::UNAUTHORIZED, "Invalid token"))?; Ok(AuthenticatedUser { id: claims.sub, role: claims.role }) } }

Authorization: In handlers, compare the requested resource ID with the user's ID or check roles. For IDOR:

async fn get_user_profile(Path(user_id): Path<u32>, auth_user: AuthenticatedUser, State(state): State<AppState>) -> Result<Json<UserProfile>, (StatusCode, &'static str)> { if auth_user.id != user_id && auth_user.role != "admin" { return Err((StatusCode::FORBIDDEN, "Not authorized")); } let profile = state.db.get_profile(user_id).await.map_err(|_| (StatusCode::NOT_FOUND, "User not found"))?; Ok(Json(profile)) }

Input Validation: Use the validator crate to validate request bodies:

#[derive(Deserialize, Validate)] struct CreateUserRequest { #[validate(length(min = 3, max = 50))] username: String, #[validate(email)] email: String, } async fn create_user(Json(payload): Json<CreateUserRequest>) -> Result<(), (StatusCode, String)> { payload.validate().map_err(|e| (StatusCode::BAD_REQUEST, e.to_string()))?; // create user Ok(()) }

Rate Limiting: Add tower-http::limit::RateLimitLayer to your router:

use tower_http::limit::RateLimitLayer; use std::time::Duration; let app = Router::new() .route("/api/login", post(login)) .layer(RateLimitLayer::new(5, Duration::from_secs(60)));

After applying these fixes, re-scan with middleBrick to confirm the vulnerabilities are resolved. Integrate middleBrick into CI/CD (e.g., GitHub Action) to prevent regressions and maintain a strong security posture.