How to fix JWT Vulnerabilities (Weak Signing, None Algo)
in Salvo
Executive Summary
JWT vulnerabilities in Salvo applications typically arise from improper use of the `jsonwebtoken` crate within custom middlewares or handlers. The most critical flaws include accepting the 'none' algorithm—which allows attackers to bypass signature verification entirely—and using weak, hardcoded HMAC secrets that are susceptible to offline brute-force attacks. Hardening your Salvo app requires strict algorithm enforcement and robust secret management.
The Vulnerable Pattern
use salvo::prelude::*; use jsonwebtoken::{decode, DecodingKey, Validation, Algorithm};#[handler] async fn insecure_handler(req: &mut Request) -> String { let token = req.headers().get(“Authorization”).unwrap().to_str().unwrap();
// VULNERABILITY 1: Weak, hardcoded secret let key = DecodingKey::from_secret("secret123".as_ref()); // VULNERABILITY 2: Allowing 'None' algorithm or failing to restrict algorithms let mut validation = Validation::default(); validation.algorithms = vec![Algorithm::HS256, Algorithm::None]; let token_data = decode::<Claims>(token, &key, &validation).unwrap(); format!("Authenticated as: {}", token_data.claims.sub)
}
The Secure Implementation
The fix addresses two primary vectors: 1. Algorithm Restriction: By using `Validation::new(Algorithm::HS256)`, we explicitly whitelist only HS256. This prevents 'alg: none' attacks where an attacker removes the signature and changes the header to bypass authentication. 2. Cryptographic Strength: Replacing the hardcoded 'secret123' with an environment variable ensures that the signing key is not leaked in source control and can be a high-entropy string, preventing brute-force tools like Hashcat from cracking the HMAC. Additionally, the secure snippet implements proper error handling and Bearer token parsing, preventing panics on malformed input.
use salvo::prelude::*; use jsonwebtoken::{decode, DecodingKey, Validation, Algorithm}; use std::env;#[handler] async fn secure_handler(req: &mut Request, res: &mut Response) { let auth_header = match req.headers().get(“Authorization”).and_then(|v| v.to_str().ok()) { Some(h) if h.starts_with(“Bearer ”) => &h[7..], _ => { res.status_code(StatusCode::UNAUTHORIZED); return; } };
// FIX 1: Load high-entropy secret from environment variables let secret = env::var("JWT_SECRET").expect("JWT_SECRET must be set"); let key = DecodingKey::from_secret(secret.as_bytes()); // FIX 2: Explicitly restrict to strong algorithms only (Never use Algorithm::None) let validation = Validation::new(Algorithm::HS256); match decode::<Claims>(auth_header, &key, &validation) { Ok(token_data) => res.render(format!("Authenticated as: {}", token_data.claims.sub)), Err(_) => res.status_code(StatusCode::UNAUTHORIZED), }
}
Your Salvo API
might be exposed to JWT Vulnerabilities (Weak Signing, None Algo)
74% of Salvo apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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