Credential Stuffing in Axum with Api Keys

Credential stuffing is an automated attack technique where previously breached username and password pairs are reused to gain unauthorized access. When Api Keys are used as the primary or secondary credential in an Axum-based API, the risk profile changes in ways that can amplify the impact of credential stuffing.

Axum, a Rust web framework, typically manages authentication via middleware that inspects request headers. If an Api Key is transmitted in a predictable header (e.g., x-api-key) and lacks binding to a specific scope, rate limits, or strong rotation, an attacker can automate submissions of known key patterns harvested from other services. Unlike passwords, Api Keys are often long-lived and rarely rotated, making them attractive targets for stuffing campaigns.

In a black-box scan, middleBrick tests unauthenticated endpoints that accept Api Keys and checks whether the same key can be reused across multiple user contexts. If key validation does not include checks for token binding (e.g., associating a key with a specific user or IP), a single compromised key can provide broad access. MiddleBrick’s Authentication and BOLA/IDOR checks will flag weak segregation between key holders and will surface excessive agency when key-based access allows actions beyond intended permissions.

Additional risk arises when Api Keys are logged, leaked in error messages, or exposed in client-side code. middleBrick’s Data Exposure and Unsafe Consumption checks detect whether keys appear in responses, logs, or error payloads. Since Api Keys often grant higher-level access than session tokens, exposure through logging or misconfigured CORS can enable large-scale credential stuffing attacks without requiring brute force.

The LLM/AI Security checks in middleBrick examine whether an endpoint accepting Api Keys also exposes an unauthenticated LLM endpoint. If a model endpoint echoes key information or responds to injected prompts with key-like values, this could facilitate exfiltration or aid an attacker in refining stuffing payloads. These probes simulate realistic attack chains that combine credential reuse with model interaction.

Because middleBrick scans in 5–15 seconds without agents or credentials, teams can quickly identify whether their Axum API’s key-based authentication is vulnerable to credential stuffing. Findings include severity ratings and remediation guidance mapped to frameworks such as OWASP API Top 10 and PCI-DSS.

Securing Api Keys in Axum requires structural changes to how keys are issued, transmitted, and validated. The following examples demonstrate concrete mitigation patterns that reduce the risk of credential stuffing.

1. Use middleware to validate key scope and binding

Instead of a global key check, bind each key to a specific set of permissions and, where possible, to a request context such as IP or user ID. This limits the blast radius if a key is compromised.

use axum::{routing::get, Router, extract::Request, middleware::Next, http::Request as HttpRequest};
use std::convert::Infallible;

async fn api_key_middleware(
    req: Request,
    next: Next,
) -> Result<axum::response::Response, Infallible> {
    let key = req.headers().get("x-api-key")
        .and_then(|v| v.to_str().ok())
        .unwrap_or("");

    // Example: validate against a store with scope and binding metadata
    if !is_valid_key_with_scope(key, req.uri().path(), req.extensions().get::().copied()) {
        return Ok(axum::response::Response::builder()
            .status(403)
            .body("Invalid or insufficient scope".into());
    }
    next.run(req).await
}

async fn handler() -> &'static str { "ok" }

fn is_valid_key_with_scope(key: &str, path: &str, ip: Option) -> bool {
    // Implement lookup against a secure store; ensure scope and IP binding
    true // placeholder
}

This pattern ensures that each request is evaluated against contextual rules, making it harder to reuse a key across different endpoints or users.

2. Rotate keys and avoid embedding them in client-side code

Do not embed static keys in JavaScript bundles or mobile binaries. Use short-lived keys where feasible and implement a rotation schedule. If your stack supports it, issue keys via a secure provisioning endpoint that requires strong authentication.

3. Enforce rate limiting and anomaly detection

Apply per-key rate limits to reduce the effectiveness of stuffing campaigns. Combine this with logging that flags unusual request volumes or geographic origins.

use axum::middleware::from_fn_with_state;

async fn rate_limit_middleware(
    State(config): State<AppConfig>,
    req: Request,
    next: Next,
) -> Result<Response, Infallible> {
    let key = req.headers().get("x-api-key").unwrap().to_str().unwrap();
    let count = config.store.record_request(key, Instant::now());
    if count > config.limits.requests_per_minute {
        return Ok(Response::builder().status(429).body("Rate limit exceeded".into()).unwrap());
    }
    next.run(req).await
}

Integrate this with your monitoring to detect bursts that are characteristic of automated stuffing attacks.

4. Avoid logging or echoing keys

Ensure that error messages and logs do not include Api Key values. middleBrick’s Data Exposure checks will highlight any occurrence of keys in responses or logs.

By combining scoped keys, contextual validation, rate limiting, and secure storage, teams can significantly lower the risk of credential stuffing against Axum services. middleBrick’s CLI and Web Dashboard make it easy to verify that these controls are effective and to track improvements over time.