Hallucination Attacks in Actix with Bearer Tokens

A hallucination attack in the context of Actix web applications using Bearer Tokens occurs when an API endpoint reflects or fabricates information about authentication, authorization, or token validity in a way that does not align with reality. Because Actix is a Rust web framework often used to build high-performance HTTP services, developers may assume that routing and handler logic alone are sufficient to enforce security. This assumption can allow an attacker to probe differences in behavior between valid and invalid tokens and infer system state or bypass authorization checks.

Bearer Tokens are typically passed in the Authorization header as Authorization: Bearer <token>. If an Actix handler does not consistently validate the token before accessing protected resources, an attacker can supply a malformed, expired, or unsigned token and observe diverging responses. A hallucination emerges when the handler unintentionally reveals whether a token was structurally valid, whether a user identity was inferred, or whether certain data exists, even when the request should be rejected. For example, an endpoint might return a 200 response with partial data for a token that appears valid but is actually revoked, or it might disclose a username in an error path that would normally be hidden. These subtle differences enable an attacker to hallucinate a valid session or privilege level without possessing a legitimate token.

The interaction between Actix middleware and routing exacerbates this risk. If token validation is implemented in a guard or a per-request handler rather than a centralized extractor or middleware layer, some routes may skip checks under certain conditions. An attacker can then craft requests that take advantage of these gaps, such as hitting a route that does not enforce extraction of the token or relies on default handler logic. Because Actix permits fine-grained control over which services and routes apply extractors, inconsistent application across the service surface creates exploitable blind spots. In addition, if error messages differ based on whether a token is present but invalid, or whether claims are missing or malformed, the application hallucinates information about the authentication state.

Consider an Actix handler that decodes a JWT but does not verify expiration or signature rigorously. An attacker can submit a token with a future expiration and observe whether the response changes compared to a token with a past expiration. The handler might inadvertently leak the claimed user ID or roles in a JSON error body, allowing the attacker to map internal identifiers. This is a hallucination attack because the system appears to enforce authorization while actually exposing information that should remain hidden. The risk is compounded when the handler mixes authorization checks with business logic, making it difficult to determine whether a given response is due to missing permissions or malformed input.

To contextualize this within common frameworks, these patterns map to the OWASP API Top 10 category Broken Object Level Authorization (BOLA) and can intersect with Injection and Security Misconfiguration. Unlike dedicated API security scanners, middleBrick performs specific checks for authentication inconsistencies and authorization leaks across unauthenticated attack surfaces. Its LLM/AI Security module includes system prompt leakage detection and active prompt injection testing, which are unrelated to this vector, but its inventory and property authorization checks help surface inconsistent enforcement in API designs. The scanner runs 12 security checks in parallel and returns a security risk score with prioritized findings and remediation guidance, highlighting routes where token validation is missing or divergent.

Remediation focuses on consistent validation, centralized extraction, and uniform error handling. In Actix, implement a dedicated extractor for Bearer Tokens and apply it uniformly across all protected routes. Avoid conditional checks that depend on route or handler differences. Use middleware or wrap handlers to guarantee that authorization decisions are made before business logic executes. Below are concrete, syntactically correct examples illustrating these practices.

First, define a Bearer token extractor that validates presence and format, and returns a standardized error response when validation fails. This extractor can be reused across services, ensuring that every route enforces the same rules.

use actix_web::{dev::Payload, Error, FromRequest, HttpMessage, HttpRequest};
use actix_web::http::header::AUTHORIZATION;
use actix_web::web::Bytes;
use futures::future::{ok, Ready};
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
pub struct AuthenticatedUser {
    pub subject: String,
    pub scopes: Vec,
}

pub struct BearerToken(pub String);

impl FromRequest for BearerToken {
    type Error = Error;
    type Future = Ready>;

    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
        let header = req.headers().get(AUTHORIZATION);
        match header {
            Some(value) => {
                if let Ok(auth_str) = value.to_str() {
                    if auth_str.starts_with("Bearer ") {
                        let token = auth_str[7..].trim();
                        if !token.is_empty() {
                            // TODO: perform signature/expiry validation here or in a later middleware step
                            return ok(BearerToken(token.to_string()));
                        }
                    }
                }
                // Hallucination mitigation: return a generic 401 without indicating why
                ok(Err(actix_web::error::ErrorUnauthorized("Unauthorized")))
            }
            None => ok(Err(actix_web::error::ErrorUnauthorized("Unauthorized"))),
        }
    }
}

Next, apply this extractor in your route definitions. By requiring the extractor, you ensure that no handler proceeds without a validated token, eliminating routes that might otherwise hallucinate access control states.

use actix_web::{web, HttpResponse};

async fn protected_endpoint(user: BearerToken) -> HttpResponse {
    // At this point, token format is verified; perform additional authorization checks as needed
    HttpResponse::Ok().json(web::Json(serde_json::json!({
        "message": "access granted",
        "token_subject": user.0
    })))
}

For centralized enforcement, wrap handlers with a middleware layer that validates scopes and expiration, and standardizes error responses. This prevents handler-specific logic from leaking information. Below is a simplified example of a middleware guard that checks a mock validation function and returns consistent 401 responses on failure.

use actix_web::{dev::{Service, ServiceResponse, Transform}, Error, HttpResponse};
use actix_web::http::Method;
use actix_web::body::BoxBody;
use std::task::{Context, Poll};
use futures::future::{ok, LocalBoxFuture};

pub struct AuthzMiddleware;

impl Transform for AuthzMiddleware
where
    S: Service, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Response = ServiceResponse;
    type Error = Error;
    type Transform = AuthzMiddlewareImpl;
    type InitError = ();
    type Future = Ready>;

    fn new_transform(&self, service: S) -> Self::Future {
        ok(AuthzMiddlewareImpl { service })
    }
}

pub struct AuthzMiddlewareImpl {
    service: S,
}

impl Service for AuthzMiddlewareImpl
where
    S: Service, Error = Error>,
    S::Future: 'static,
    B: 'static,
{
    type Response = ServiceResponse;
    type Error = Error;
    type Future = LocalBoxFuture<'static, Result>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll> {
        self.service.poll_ready(cx)
    }

    fn call(&mut self, req: ServiceRequest) -> Self::Future {
        // Example: enforce bearer token presence and basic format before proceeding
        let auth_header = req.headers().get("authorization");
        let valid = match auth_header {
            Some(h) => h.to_str().map(|s| s.starts_with("Bearer ")).unwrap_or(false),
            None => false,
        };
        if !valid {
            let response = ServiceResponse::new(
                req.into_parts().0,
                BoxBody::new(HttpResponse::Unauthorized().body("Unauthorized").into_body()),
            );
            return Box::pin(async { Ok(response) });
        }
        let fut = self.service.call(req);
        Box::pin(async move {
            let res = fut.await?;
            // Additional checks such as scope validation could be applied here
            Ok(res)
        })
    }
}