Bola Idor in Rocket with Hmac Signatures

Broken Object Level Authorization (BOLA) is an API security risk where an attacker can access or modify resources that belong to another user by manipulating object identifiers such as IDs. In the Rocket web framework for Rust, this commonly occurs when a route uses a user-supplied identifier (e.g., /users/123/account) and performs a lookup without confirming that the authenticated subject owns or is authorized to access that resource. When Hmac Signatures are used for request authentication or integrity checks—such as signing query parameters, API keys, or webhook payloads—misconfiguration can inadvertently create or expose BOLA vulnerabilities.

Consider a Rocket endpoint that accepts a signed identifier to locate a resource. If the signature only protects the integrity of the ID (e.g., to prevent tampering) but does not enforce authorization checks, an attacker can reuse a valid signed ID belonging to another user. Because the signature is valid, the server processes the request and returns data the attacker should not see. For example, a route GET /resources/:id might verify an Hmac signature on id but then directly load the resource without checking ownership. This combination leads to Insecure Direct Object References (IDOR), a classic BOLA manifestation.

Hmac Signatures can also introduce BOLA when they are used to authenticate API calls or webhooks without correlating the signing key or shared secret to a specific subject or scope. If multiple users or services share a key, or if a key is long-lived and leaked, an attacker can forge valid signed requests for other users' resources. In Rocket, this can happen when signing logic does not bind the signature to a principal, tenant, or contextual claim (such as a user ID or role). The signature ensures the request has not been altered, but it does not guarantee the requester is allowed to act on the target resource.

Another scenario involves path-based or query-parameter signatures where an attacker modifies non-identifier parameters while keeping the signature valid for the original parameters. If the server only validates the signature on a subset of parameters and then performs an access control decision based on unchecked inputs, BOLA can occur. For instance, a signed request might include user_id=100 in the payload, but the server uses current_user.id only for some checks and for others relies on the signed user_id. This inconsistency can lead to privilege escalation across accounts.

Real-world attack patterns mirror these risks. For example, an attacker might capture a legitimate request with a valid Hmac-signed ID, then replay it with a different ID if authorization is not re-evaluated. Common CWE entries relevant here include CWE-639 (Authorization Bypass Through User-Controlled Key) and CWE-287 (Improper Authentication When Using Public Key). In the context of OWASP API Security Top 10, this aligns with Broken Object Level Authorization (API1:2023). middleBrick detects such issues by correlating runtime behavior with OpenAPI/Swagger specifications, including $ref resolution, to identify endpoints where identifiers are used without proper ownership or scope-bound checks.

When using Rocket with Hmac Signatures, developers must ensure signatures are tied to the authorization context and not treated as a substitute for access control. The presence of a valid signature should not skip ownership verification, tenant isolation, or role-based checks. Continuous scanning and code review focused on the relationship between authentication signatures and resource-level permissions are essential to prevent BOLA in this setup.

To remediate BOLA when using Hmac Signatures in Rocket, bind signatures to the authorization context and enforce strict ownership checks on every request. Do not rely on signature validity alone to authorize access. Below are concrete, realistic code examples that demonstrate secure patterns.

1. Tying Hmac Signatures to User Identity

Ensure the signed payload includes a user identifier and that the server validates both the signature and that the identifier matches the current subject. Use constant-time comparison and avoid leaking timing information.

use rocket::http::Status;
use rocket::request::{self, FromRequest, Request};
use rocket::Outcome;
use hmac::{Hmac, Mac};
use sha2::Sha256;

type HmacSha256 = Hmac<Sha256>;

struct AuthenticatedUser {
    user_id: i64,
    scopes: Vec<String>,
}

struct ApiKey {
    user_id: i64,
    key_id: String,
}

#[rocket::async_trait]
impl<'r> FromRequest<'r> for AuthenticatedUser {
    type Error = ();

    async fn from_request(req: &'r Request<'_>) -> request::Outcome<Self, Self::Error> {
        // Extract signature and payload from headers
        let signature = match req.headers().get_one("X-API-Signature") {
            Some(s) => s,
            None => return Outcome::Error((Status::Unauthorized, ())),
        };
        let key_id = match req.headers().get_one("X-Key-ID") {
            Some(k) => k,
            None => return Outcome::Error((Status::Unauthorized, ())),
        };
        let timestamp = match req.headers().get_one("X-Timestamp") {
            Some(t) => t,
            None => return Outcome::Error((Status::Unauthorized, ())),
        };
        // Prevent replay attacks by checking timestamp window (example: 300 seconds)
        // ...

        // Retrieve the key securely (e.g., from a vault or database)
        let stored_key = match get_hmac_key_by_id(key_id).await {
            Some(k) => k,
            None => return Outcome::Error((Status::Unauthorized, ())),
        };

        // Verify signature over a canonical string that includes user_id
        let mut mac = HmacSha256::new_from_slice(&stored_key).expect("HMAC can take key of any size");
        // Canonical payload: timestamp + key_id + user_id (example)
        mac.update(timestamp.as_bytes());
        mac.update(key_id.as_bytes());
        // The user_id is part of the signed payload, ensuring signature ties to identity
        let payload = format!("{}", /* user_id from a trusted source */ 0);
        mac.update(payload.as_bytes());

        match mac.verify_slice(signature.as_bytes()) {
            Ok(_) => {
                // At this point, the signature is valid and tied to the payload's user_id
                // Ensure the user_id from payload matches the resource ownership checks downstream
                Outcome::Success(AuthenticatedUser { user_id: 0, scopes: vec![] }) // populate from payload
            }
            Err(_) => Outcome::Error((Status::Unauthorized, ())),
        }
    }
}

// Example protected route: the user can only access their own resources
#[get("/resources/")]
async fn get_resource(id: i64, user: AuthenticatedUser) -> Result<String, Status> {
    // BOLA check: ensure the resource belongs to the authenticated user
    let resource = fetch_resource_by_id(id).await;
    match resource {
        Some(r) => {
            if r.owner_id != user.user_id {
                return Err(Status::Forbidden);
            }
            Ok(format!("Resource: {:?}", r))
        }
        None => Err(Status::NotFound),
    }
}

2. Per-Request Scope Binding and Continuous Verification

For endpoints that accept identifiers as parameters, validate ownership on every request. Do not assume that a valid signature on an ID implies permission to access that ID across different contexts.

#[get("/users//settings")]
async fn get_user_settings(user_id: i64, user: AuthenticatedUser) -> Result<Json<Settings>, Status> {
    // BOLA mitigation: confirm the requested user_id matches the authenticated subject
    if user_id != user.user_id {
        return Err(Status::Forbidden);
    }
    let settings = fetch_settings_for_user(user_id).await;
    Ok(Json(settings))
}

3. Avoid Shared Keys Across Tenants or Users

If your system supports multi-tenancy, use tenant-specific keys and include the tenant identifier in the signed payload. This prevents cross-tenant access even if a signature is valid.

struct TenantApiKey {
    tenant_id: i64,
    key: Vec<u8>,
}

async fn verify_tenant_signature(
    tenant_id: i64,
    payload: &str,
    signature: &str,
) -> bool {
    let key = match get_tenant_key(tenant_id).await {
        Some(k) => k,
        None => return false,
    };
    let mut mac = HmacSha256::new_from_slice(&key).expect("HMAC can take key of any size");
    mac.update(payload.as_bytes());
    matches!(mac.verify_slice(signature.as_bytes()), Ok(()))
}

4. Use Short-Lived, Scoped Signatures

Prefer short expiration windows and include scope claims in the signed data. Rotate keys regularly and revoke compromised keys immediately. This reduces the impact of a leaked signature and limits the window for BOLA exploitation.

5. Combine Signatures with RBAC/ABAC Checks

Hmac Signatures should authenticate and integrity-protect the request, but authorization must be evaluated separately using role-based or attribute-based controls. In Rocket, implement guards that evaluate permissions after signature validation.

fn has_permission(user: &AuthenticatedUser, resource: &Resource) -> bool {
    // Example: check user roles or scopes against required permissions
    user.scopes.contains("read:resource".to_string()) && resource.scope == "user"
}

By binding Hmac Signatures to identity, validating ownership on every request, avoiding shared keys, using scoped short-lived tokens, and layering explicit authorization checks, you mitigate BOLA risks in Rocket applications while retaining the integrity benefits of Hmac Signatures.