Jwt Misconfiguration in Axum with Dynamodb

JWT misconfiguration in an Axum service that uses DynamoDB as a persistence layer can expose authentication bypass or privilege escalation risks. Axum is a Rust web framework where developers compose middleware and extractors to enforce authentication. If JWT validation is incomplete, an attacker can exploit gaps such as missing issuer checks, weak algorithm enforcement, or absent token binding to session state stored in DynamoDB.

DynamoDB stores user identities, roles, and session metadata. When Axum decodes a JWT and then queries DynamoDB to confirm permissions or session validity, inconsistencies between token claims and database records become exploitable. For example, if Axum trusts the sub claim without verifying that the subject exists and is active in DynamoDB, a static or forged token may grant access. Similarly, if the token lacks a jti (JWT ID) or the application does not check token revocation in DynamoDB, stolen or rotated credentials remain valid.

A concrete attack chain: an attacker obtains a leaked JWT from a misconfigured client or logs; the token uses HS256 with a weak secret or none algorithm due to Axum middleware misconfiguration; DynamoDB does not enforce a one-time-use or short-lived pattern; and the application skips scope/role validation against DynamoDB records. This can lead to horizontal or vertical privilege escalation, for example accessing admin endpoints by changing a role claim if Axum does not revalidate authorization against DynamoDB on each request.

SSRF and injection are not direct causes here, but unsafe token handling can amplify issues. For instance, Axum code that embeds user identifiers from JWT claims into DynamoDB queries without sanitization may open injection-like behavior in application logic. Proper validation, strict algorithm selection, and consistent state checks against DynamoDB mitigate these risks.

Remediation centers on strict JWT validation in Axum and authoritative checks against DynamoDB. Use a well-maintained crate such as jsonwebtoken for decoding and validating tokens, and the official AWS SDK for Rust to interact with DynamoDB. Enforce algorithm, issuer, audience, and expiration checks in Axum, then confirm the subject and permissions against DynamoDB on every authenticated request.

Example Axum middleware that validates JWT and rechecks authorization with DynamoDB:

use axum::{async_trait, extract::Request, middleware, response::Response, Extension};
use jsonwebtoken::{decode, Algorithm, DecodingKey, Validation};
use serde::{Deserialize, Serialize};
use aws_sdk_dynamodb::Client as DynamoClient;

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

async fn validate_jwt_and_dynamodb(
    token: &str,
    dynamo_client: &DynamoClient,
    expected_issuer: &str,
    expected_audience: &str,
) -> Result {
    let mut validation = Validation::new(Algorithm::HS256);
    validation.set_issuer(&[expected_issuer]);
    validation.set_audience(&[expected_audience]);
    validation.validate_exp = true;

    let token_data = decode::(
        token,
        &DecodingKey::from_secret("YOUR_STRONG_SECRET".as_ref()),
        &validation,
    ).map_err(|e| format!("JWT decode error: {:?}", e))?;

    // Check revocation or session state in DynamoDB using jti
    let item = dynamo_client.get_item()
        .table_name("auth_tokens")
        .key("jti", aws_sdk_dynamodb::types::AttributeValue::S(token_data.claims.jti.clone()))
        .send()
        .await
        .map_err(|e| format!("DynamoDB error: {:?}", e))?;

    if item.item().is_none() {
        return Err("Token not found or revoked".into());
    }

    // Optionally re-check user status
    let user_item = dynamo_client.get_item()
        .table_name("users")
        .key("sub", aws_sdk_dynamodb::types::AttributeValue::S(token_data.claims.sub.clone()))
        .send()
        .await
        .map_err(|e| format!("DynamoDB error: {:?}", e))?;

    if user_item.item().and_then(|i| i.get("enabled")).and_then(|v| v.as_bool()) != Some(true) {
        return Err("User disabled".into());
    }

    Ok(token_data.claims)
}

// Axum middleware example
pub async fn auth_middleware(
    req: Request,
    Extension(dynamo_client): Extension,
) -> Result {
    let auth_header = req.headers().get("authorization")
        .and_then(|v| v.to_str().ok())
        .ok_or_else(|| Response::builder().status(401).body("Missing authorization".into()).unwrap())?;
    let token = auth_header.strip_prefix("Bearer ").ok_or_else(|| Response::builder().status(401).body("Invalid auth format".into()).unwrap())?;

    let claims = validate_jwt_and_dynamodb(
        token,
        &dynamo_client,
        "https://myapi.example.com",
        "myapi-client",
    ).await.map_err(|_| Response::builder().status(403).body("Forbidden".into()).unwrap())?;

    // Attach claims for downstream handlers
    Ok(req.extensions().with(claims))
}

Key remediation steps:

• Enforce a strong secret and HS256 (or RS256) in Axum middleware; reject none and unset algorithms.
• Validate iss, aud, exp, and use jti to check token state in DynamoDB.
• Ensure DynamoDB tables have fine-grained access controls and store revocation or session state (e.g., active jti entries).
• On each request, re-validate critical authorization claims against DynamoDB to prevent stale or elevated privileges.
• Use short token lifetimes and refresh workflows, storing refresh token metadata in DynamoDB with appropriate TTL.

These measures align with the checks in middleBrick’s Authentication, BOLA/IDOR, and Property Authorization scans, which map findings to frameworks like OWASP API Top 10 and SOC2.