Symlink Attack in Axum with Cockroachdb

A symlink attack in an Axum service that uses CockroachDB can occur when user-controlled input influences file system paths used during backup, migration, or log operations, and those operations are executed in a context where database credentials or connection strings are accessible via the file system. For example, an Axum handler that receives a filename parameter and writes a CockroachDB dump to that path without validating or sanitizing the input can allow an attacker to supply a path that resolves to a sensitive location. If the application later reads from that path with higher privileges (for instance, to restore the dump into the CockroachDB cluster), the attacker can replace the intended file with a symlink that points to a critical system file or a CockroachDB configuration file containing connection details.

When combined with CockroachDB, the risk surface expands if the application stores or references database credentials, certificates, or connection URIs as files on disk. An attacker who can redirect a file write to a location that the CockroachDB client or an auxiliary script reads may gain insight into authentication mechanisms or be able to inject malicious SQL by influencing a restore operation. Even in a black-box scan with no credentials, middleBrick can detect indicators such as unauthenticated endpoints that accept file paths and show that user input flows into system-level operations, helping to highlight the presence of path traversal or symlink-prone handlers.

In practice, this vulnerability is not about breaking CockroachDB itself but about the surrounding integration in Axum where file system operations are tied to database workflows. An OpenAPI spec analyzed by middleBrick might define a backup endpoint without clarifying that the provided filename is used server-side in file system calls; runtime testing could then surface that unauthenticated probes reach handlers that write files. The combination of Axum routing, unchecked path usage, and CockroachDB-related artifacts on disk creates a scenario where an attacker can manipulate file references to gain information or set up conditions for further exploitation.

Remediation centers on strict input validation, avoiding direct filesystem operations with user input, and isolating database credentials from file system paths. In Axum, prefer using typed configuration and environment variables for CockroachDB connection strings rather than reading credentials from files that user input could influence. If you must write files related to backups or migrations, generate deterministic, server-side filenames and store them outside of publicly reachable or user-controlled directories.

Use path sanitization and canonicalization before any file operation, and resolve paths against a strict base directory to prevent symlink escapes. The following Axum handler demonstrates a safe approach that avoids using user input as a filesystem path and instead uses a server-generated filename while interacting with CockroachDB via a secure connection string sourced from environment variables.

use axum::{routing::post, Router};
use std::net::SocketAddr;
use cockroachdb_rs::Client; // hypothetical client for illustration
use std::env;
use uuid::Uuid;

async fn backup_handler() -> Result {
    // Read CockroachDB connection details from environment, not from user-controlled files
    let db_url = env::var("COCKROACH_URL").map_err(|_| {
        (axum::http::StatusCode::INTERNAL_SERVER_ERROR, "Server configuration missing".to_string())
    })?;

    // Generate a server-side filename to avoid path injection
    let filename = format!("backup-{}.sql", Uuid::new_v4());
    let base_dir = "/srv/app/backups"; // a non-user-controlled directory
    let path = std::path::Path::new(base_dir).join(filename);

    // Ensure the base directory exists and is not writable by untrusted users
    tokio::fs::create_dir_all(base_dir).await.map_err(|e| {
        (axum::http::StatusCode::INTERNAL_SERVER_ERROR, format!("Backup directory error: {e}"))
    })?;

    // Use a CockroachDB client to perform a backup operation
    let client = Client::new(&db_url).await.map_err(|e| {
        (axum::http::StatusCode::INTERNAL_SERVER_ERROR, format!("Database connection error: {e}"))
    })?;

    // Example: invoke a backup routine that writes to the server-side path
    client.backup_to_path(&path).await.map_err(|e| {
        (axum::http::StatusCode::INTERNAL_SERVER_ERROR, format!("Backup failed: {e}"))
    })?;

    Ok(filename)
}

#[tokio::main]
async fn main() {
    let app = Router::new().route("/backup", post(backup_handler));
    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
    axum::Server::bind(&addr)
        .serve(app.into_make_service())
        .await
        .unwrap();
}

Key practices include: never using user input as a direct filesystem path, resolving all paths against a strict allowlist base directory, storing CockroachDB credentials in environment variables or a secure configuration service, and ensuring that any generated artifacts are created with restrictive filesystem permissions. These measures reduce the attack surface for symlink-based techniques targeting the Axum-CockroachDB integration.