Webhook Abuse in Axum with Basic Auth

Webhook Abuse in Axum with Basic Auth centers on how an endpoint that accepts webhook notifications can be triggered without proper authorization when Basic Auth is used naively or omitted. In Axum, a webhook handler often receives HTTP requests from third‑party services that expect a shared secret or token to prove identity. If the route is protected only by Basic Auth, an attacker who knows or guesses the username/password can call the webhook endpoint directly, bypassing any application‑level webhook secret verification. This is a BOLA/IDOR and BFLA/Privilege Escalation concern: the endpoint may perform elevated actions (e.g., triggering deployments, modifying resources) because the handler trusts the Basic Auth credentials alone.

Basic Auth transmits credentials as base64‑encoded, not encrypted, payloads unless used over TLS. In Axum, middleware or extractor-based auth can be added to require a username and password on the webhook route. However, if you rely solely on Basic Auth without additional webhook‑specific validation (such as validating a signature header or a dedicated token), any compromised or leaked credentials allow unauthenticated‑style abuse from the attacker’s perspective, because the endpoint does not differentiate between a legitimate upstream service and an attacker providing the same credentials. Attack patterns include replay of intercepted requests, credential stuffing against weak passwords, and exploiting default or weakly‑protected admin accounts used for the integration.

An additional risk specific to the combination is that Basic Auth may be used inconsistently across services: some upstream providers may send signed requests, while the Axum handler only checks Basic Auth. This inconsistency can be abused if an attacker identifies the route and learns the Basic Auth credentials through source code exposure, logs, or accidental disclosure. Once obtained, they can forge requests that appear authenticated, potentially triggering unsafe consumption actions or excessive agency if the handler performs operations with broad permissions. The scan checks flag this as a risk when a webhook route lacks layered validation and relies only on transport‑level credentials without runtime signature or token verification, mapping to OWASP API Top 10:2023 A01:Broken Access Control and A07:2023 Identification and Authentication Failures.

In testing, middleBrick runs checks against the unauthenticated attack surface and, when credentials are supplied, validates whether the endpoint’s behavior changes inappropriately based on identity. Findings include missing webhook signature validation, missing scope‑based authorization, and missing rate limiting that could enable brute‑force or credential‑guessing attacks. Remediation guidance emphasizes adding webhook‑level secrets or signatures, tightening authentication scope, and ensuring TLS is enforced, which aligns with compliance frameworks such as PCI‑DSS and SOC2 controls around authentication and integrity.

To secure a webhook endpoint in Axum with Basic Auth, combine transport‑level credentials with explicit validation inside your handler. Below are concrete, realistic code examples that demonstrate how to require Basic Auth and add webhook‑specific verification in Axum.

1) Basic Auth extractor with username/password check:

use axum::{
    async_trait, extract::FromRequest, http::request::Parts, response::IntoResponse,
    routing::post, Router,
};
use std::convert::Infallible;
use headers::authorization::{Authorization, Basic};

// A simple extractor that requires a specific username/password.
struct Authenticated;

#[async_trait]
impl FromRequest<S> for Authenticated
where
    S: Send + Sync,
{
    type Rejection = impl IntoResponse;

    async fn from_request(req: Parts, _state: &S) -> Result {
        let headers = req.headers;
        let authorization = headers.get("authorization")
            .and_then(|v| v.to_str().ok())
            .and_then(|s| s.parse::>().ok())
            .ok_or((StatusCode::UNAUTHORIZED, "missing basic auth"))?;

        let user = authorization.user_id();
        let pass = authorization.password().unwrap_or("");

        // Replace with secure credential checks (e.g., constant-time compare).
        if user == "webhook_user" && pass == "StrongSharedSecret123!" {
            Ok(Authenticated)
        } else {
            Err((StatusCode::FORBIDDEN, "invalid credentials").into_response())
        }
    }
}

async fn webhook_handler() -> impl IntoResponse {
    // Process webhook payload with additional webhook‑level validation here.
    (StatusCode::OK, "received")
}

let app = Router::new()
    .route("/webhook", post(webhook_handler))
    .layer(axum::middleware::from_fn_with_state(
        (),
        |_, handler| async move { Ok::<_, Infallible>(handler.run(...).await) },
    ));
// Protect the route by requiring Authenticated extractor.
let app = app.route("/webhook", post(|authenticated: Authenticated| async { webhook_handler() }));

use axum::{http::StatusCode, extract::Query, response::IntoResponse};
use hmac::{Hmac, Mac};
use sha2::Sha256;

type HmacSha256 = Hmac<Sha256>;

async fn webhook_handler(
    auth: Authenticated,
    headers: HeaderMap,
    body: String,
) -> impl IntoResponse {
    // Verify webhook signature in addition to Basic Auth.
    let signature = headers.get("x-hub-signature-256")
        .and_then(|v| v.to_str().ok())
        .unwrap_or("");
    let body_bytes = body.as_bytes();
    let secret = b"webhook_shared_secret";

    let mut mac = HmacSha256::new_from_slice(secret).expect("valid key length");
    mac.update(body_bytes);
    let result = mac.finalize();
    let computed = result.into_bytes();

    // Convert header value "sha256=..." to hex.
    if let Some(hex) = signature.strip_prefix("sha256=") {
        if hex::decode(hex).map(|expected| subtle::ConstantTimeEq::ct_eq(&computed[..], expected.as_ref()).into()).unwrap_or(false) {
            // Signature and Basic Auth both valid; process webhook.
            return (StatusCode::OK, "verified");
        }
    }
    (StatusCode::UNAUTHORIZED, "invalid signature")
}

// Enforce HTTPS in production by rejecting non‑TLS requests at the gateway or with a middleware check.
// Example: reject non‑TLS in middleware (conceptual).
async fn require_https(req: Request<B>, next: Next<B>) -> Result<impl IntoResponse, (StatusCode, String)> {
    if req.uri().scheme() != &hyper::http::uri::Scheme::HTTPS {
        return Err((StatusCode::FORBIDDEN, "HTTPS required".to_string()));
    }
    Ok(next.run(req).await)
}