Unicode Normalization in Axum with Cockroachdb

Unicode normalization issues arise when an application compares or stores text without ensuring a canonical form. In Axum, user-controlled strings such as usernames, identifiers, or search parameters may be accepted and then used in SQL queries sent to Cockroachdb. Cockroachdb stores text in Unicode Normalization Form C (NFC) for certain collations, but it does not automatically normalize inputs before comparison or indexing. If Axum passes unnormalized strings to Cockroachdb, equivalent characters can bypass lookups, cause duplicate entries, or lead to inconsistent authorization checks. For example, a decomposed string with combining accents may not match its precomposed NFC counterpart stored in a USERS table, resulting in authentication or authorization logic that incorrectly treats two visually identical identifiers as different or, conversely, treats different strings as identical.

These inconsistencies can affect BOLA/IDOR checks when an object identifier is derived from a user-supplied string that appears equivalent but normalizes differently, allowing horizontal or vertical privilege escalation. Input validation that relies on exact string matching may also be bypassed if normalization is not applied consistently across Axum and Cockroachdb. In addition, data exposure and unsafe consumption checks can be impacted when normalized and non-normalized representations of the same data are stored or returned, leading to inadvertent information disclosure or application logic errors.

To detect this using middleBrick’s 12 security checks, the scanner tests how Axum handles equivalent Unicode inputs and cross-references findings with Cockroachdb’s normalization behavior defined in the OpenAPI spec. Findings include severity-ranked guidance on normalization strategies, such as NFC normalization before storage and comparison, and mapping to relevant compliance frameworks like OWASP API Top 10 and GDPR.

Remediation centers on ensuring canonical Unicode representation before any database interaction. In Axum, implement a normalization layer that converts incoming text to NFC using a well-tested Unicode library before constructing SQL queries. Below is a concrete example using rust_icu_normalizer and sqlx with Cockroachdb. This approach ensures consistent encoding for identifiers, usernames, and searchable fields, mitigating comparison mismatches and BOLA/IDOR risks.

// Axum handler with NFC normalization before Cockroachdb interaction
use axum::{
    extract::Query,
    response::IntoResponse,
    routing::get,
    Router,
};
use rust_icu_normalizer::Normalizer;
use serde::Deserialize;
use sqlx::postgres::PgPoolOptions;
use std::net::SocketAddr;

#[derive(Deserialize)]
pub struct UserParams {
    pub username: String,
}

async fn get_user(
    Query(params): Query,
    pool: &axum::extract::State<sqlx::PgPool>
) -> impl IntoResponse {
    // Normalize to NFC before using in SQL
    let normalized_username = params.username.nfc().collect::();
    let user: (String,) = sqlx::query_as("SELECT username FROM users WHERE username = $1")
        .bind(&normalized_username)
        .fetch_one(&pool.0)
        .await
        .expect("Failed to fetch user");
    format!("User: {}", user.0)
}

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let pool = PgPoolOptions::new()
        .connect("postgresql://user:password@localhost/dbname?sslmode=require")
        .await
        .expect("Failed to create pool");
    let app = Router::new()
        .route("/user", get(get_user))
        .with_state(pool);
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
    Ok(())
}

Additionally, ensure that Cockroachdb column collations are explicitly set to a Unicode-aware collation if available, and avoid relying on implicit normalization. For existing data, run a one-time normalization migration to bring all entries into NFC. middleBrick’s CLI can be used to scan Axum endpoints against Cockroachdb integrations; the middlebrick scan <url> command will highlight inconsistencies between spec-defined normalization expectations and runtime behavior, including checks mapped to OWASP API Top 10 and compliance frameworks.

For continuous monitoring, the Pro plan provides scheduled scans and change detection, while the GitHub Action can fail builds if new endpoints introduce non-normalized inputs. The MCP Server allows you to validate Unicode handling directly from your AI coding assistant within the IDE, reducing the risk of introducing inconsistent text handling across Axum routes and Cockroachdb queries.