Password Spraying in Chi with Jwt Tokens

In Chi, a common pattern is to issue a JWT token after verifying a username and password. Password spraying becomes particularly relevant when an attacker targets many accounts with a small list of likely passwords, attempting to authenticate and obtain a JWT token for each. Because Chi applications often rely on JWT tokens for subsequent authorization, an attacker who successfully obtains a token can make privileged requests until the token expires.

When endpoints in Chi validate credentials and immediately return a JWT token without additional protections, password spraying can be more effective. The attacker iterates over user accounts, sending a single password attempt per account to avoid account lockout, while the application issues a JWT for any valid credentials. If the application does not enforce rate limiting or anomaly detection at the authentication endpoint, this behavior can go unnoticed.

Chi applications that accept JWT tokens via the Authorization header (Bearer scheme) may also be vulnerable when tokens are accepted without strict validation. For example, if a token is accepted even when issued for a different audience or scope, an attacker can reuse a token obtained via password spraying across multiple endpoints. The presence of weak token binding, missing nonce checks, or permissive CORS settings can further expand the impact of password spraying combined with JWT usage.

OpenAPI specifications in Chi sometimes describe security schemes using bearerAuth with type http and scheme bearer, but may omit critical details like required scopes or audience constraints. Attackers can leverage this ambiguity by attempting password spraying against endpoints documented as requiring a JWT token, especially when the authentication endpoint itself does not enforce strong protections.

Real-world attack patterns observed in the wild include spraying passwords like P@ssw0rd1 or Welcome1 across a list of known usernames, then using any resulting JWT tokens to access user data or administrative routes. Because Chi applications often centralize authentication logic, a weakness in how tokens are issued or validated can amplify the risk of password spraying.

To reduce the risk of password spraying when using JWT tokens in Chi, apply strong authentication controls and tighten token validation. The following code examples show concrete remediation steps using Chi and related libraries.

1. Enforce rate limiting on the login endpoint

Limit login attempts per IP or user to slow down spraying. The following example uses a simple in-memory rate limiter in Chi:

use chiuse chi::Router;
use std::collections::HashMap;
use std::sync::{Arc, Mutex};

struct RateLimiter {
    attempts: HashMap,
}

impl RateLimiter {
    fn new() -> Self {
        Self { attempts: HashMap::new() }
    }

    fn allow(&mut self, key: &str) -> bool {
        let count = self.attempts.entry(key.to_string()).or_insert(0);
        *count += 1;
        // Allow at most 5 attempts per key per window (simplified)
        *count <= 5
    }
}

fn login_handler(limiter: Arc<Mutex<RateLimiter>>, username: String) -> String {
    let mut limiter = limiter.lock().unwrap();
    let key = format!("login:{}", username);
    if limiter.allow(&key) {
        // proceed with credential checks
        "Login processed".to_string()
    } else {
        "Too many attempts".to_string()
    }
}

// In your route:
let limiter = Arc::new(Mutex::new(RateLimiter::new()));
let login_route = chi::route::get("/login", move |req: &mut chi::Request| {
    let limiter = limiter.clone();
    let username = req.url_params().get("username").unwrap_or("").to_string();
    let response = login_handler(limiter, username);
    Ok(chi::Response::new().body(response))
});

2. Validate JWT audience and issuer strictly

Ensure tokens are only accepted for the intended audience and issuer. Example using the jsonwebtoken crate:

use jsonwebtoken::{decode, Algorithm, DecodingKey, Validation, TokenData};
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
struct Claims {
    sub: String,
    exp: usize,
    aud: String,
    iss: String,
}

fn validate_token(token: &str) -> Result<TokenData<Claims>, jsonwebtoken::errors::Error> {
    let mut validation = Validation::new(Algorithm::HS256);
    validation.set_audience(&["my-chi-app"]);
    validation.set_issuer(&["https://auth.myapp.com"]);
    validation.validate_exp = true;

    decode::