Session Fixation in Axum with Cockroachdb

Session fixation occurs when an application accepts a session identifier provided by the client without validating or regenerating it. In an Axum application that uses Cockroachdb as the session store, the risk centers on how session identifiers are created, stored, and associated with user data.

Axum is a web framework built on asynchronous Rust, and it does not enforce session management by default. Developers typically introduce sessions via middleware or custom state, often storing session data in external databases like Cockroachdb. Cockroachdb, a distributed SQL database, is commonly used to persist session records because of its strong consistency and horizontal scalability. However, the combination of Axum and Cockroachdb does not inherently protect against session fixation; it depends on implementation choices.

If an Axum application creates a session identifier client-side (e.g., in a cookie) and then stores it in Cockroachdb without ensuring uniqueness and unpredictability, an attacker can craft a known session ID and trick a victim into authenticating with that ID. Because Cockroachdb records are keyed by session identifiers, the attacker can later use the same identifier to hijack the authenticated session. This pattern is common when session state is stored in a relational store but session creation logic is not tightly coupled with authentication events.

Another vector arises when Axum endpoints read session identifiers from cookies or headers and directly query Cockroachdb to fetch session data without verifying whether the session was originally issued by the server. If the application does not enforce session regeneration after login (a common oversight), the pre-authentication session identifier persists into the post-authentication state. An attacker who knows this identifier can maintain access even after the victim authenticates, because the server continues to treat the supplied identifier as valid.

The database schema also plays a role. A typical Cockroachdb table for sessions might include columns such as session_id (primary key), user_id, expires_at, and payload. If session_id values are predictable (e.g., sequential integers or non-random UUIDs), or if they are not bound tightly to user context and expiration, the attack surface widens. Moreover, if the Axum application does not enforce strict cookie attributes like HttpOnly, Secure, and SameSite, the session identifier can be leaked through cross-site scripting or transmitted over insecure channels, compounding the fixation risk in a Cockroachdb-backed system.

Because this scanning tool evaluates unauthenticated attack surfaces, it can detect indicators such as predictable session identifiers, missing regeneration after authentication, and overly permissive cookie settings when reviewing API interactions with Cockroachdb-backed session logic. These findings highlight where the Axum application and its Cockroachdb persistence layer fail to break the attacker’s ability to fixate a session identifier.

Remediation focuses on ensuring that session identifiers are generated securely, bound to authentication events, and stored with strict validation in Cockroachdb. Below are concrete Axum patterns with syntactically correct Cockroachdb interaction code.

First, generate cryptographically random session identifiers and store them alongside metadata in Cockroachdb. Use the uuid crate to create version 4 UUIDs and bind them to user identifiers and expiration timestamps.

use axum::{routing::post, Router};
use cockroachdb_rs::Client; // hypothetical Cockroachdb client wrapper
use serde::{Deserialize, Serialize};
use std::net::SocketAddr;
use uuid::Uuid;

#[derive(Serialize, Deserialize)]
struct SessionRecord {
    session_id: String,
    user_id: i64,
    expires_at: chrono::DateTime<chrono::Utc>,
}

async fn create_session(user_id: i64, db_client: &Client) -> String {
    let session_id = Uuid::new_v4().to_string();
    let expires_at = chrono::Utc::now() + chrono::Duration::hours(1);
    let record = SessionRecord {
        session_id: session_id.clone(),
        user_id,
        expires_at,
    };
    // Insert or replace session in Cockroachdb
    db_client.execute(
        "INSERT INTO sessions (session_id, user_id, expires_at) VALUES ($1, $2, $3)",
        &[&record.session_id, &record.user_id, &record.expires_at],
    ).await.unwrap();
    session_id
}

#[tokio::main]
async fn main() {
    let db_client = Client::new("postgresql://root@localhost:26257/defaultdb?sslmode=disable").unwrap();
    let app = Router::new().route("/login", post(move |user_id: i64| async move {
        let sid = create_session(user_id, &db_client).await;
        (axum::http::StatusCode::OK, sid)
    }));
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    axum::Server::bind(&addr).serve(app.into_make_service()).await.unwrap();
}

Second, enforce session regeneration upon authentication to break fixation. After validating credentials, create a new session identifier, store it in Cockroachdb, and retire the old one. This ensures that even if an attacker provided a session ID, it is not reused after login.

async fn rotate_session(old_session_id: &str, user_id: i64, db_client: &Client) -> String {
    // Delete the old session to prevent reuse
    db_client.execute(
        "DELETE FROM sessions WHERE session_id = $1",
        &[&old_session_id],
    ).await.unwrap();
    create_session(user_id, db_client).await
}

Third, validate the session on each request by querying Cockroachdb and checking expiration and ownership. Do not trust client-supplied identifiers without server-side verification.

async fn validate_session(session_id: &str, user_id: i64, db_client: &Client) -> bool {
    let row = db_client.query_one_opt(
        "SELECT expires_at FROM sessions WHERE session_id = $1 AND user_id = $2",
        &[&session_id, &user_id],
    ).await.unwrap();
    match row {
        Some(record) => {
            let expires: chrono::DateTime<chrono::Utc> = record.get(0);
            expires > chrono::Utc::now()
        }
        None => false,
    }
}

Finally, configure secure cookie attributes in Axum to mitigate transmission risks. Use Cookie settings with secure, http_only, and same_site policies to ensure session identifiers are not exposed to scripts or transmitted over non-HTTPS channels.

let cookie = (
    "session_id",
    cookie::Cookie::build(("session_id", session_id))
        .secure(true)
        .http_only(true)
        .same_site(cookie::SameSite::Strict)
        .path("/")
        .finish(),
);

These patterns ensure that session identifiers are unpredictable, tied to authentication events, and verified against Cockroachdb state, effectively neutralizing session fixation in an Axum application.