Sandbox Escape in Axum with Cockroachdb

A sandbox escape in the context of an Axum service using CockroachDB occurs when an attacker is able to move from a constrained execution or query context into the host system or broader infrastructure. Axum is a web framework for building HTTP services in Rust, and CockroachDB is a distributed SQL database often deployed in Kubernetes or cloud environments. The combination can expose risks if the API surface does not properly validate inputs, enforce least-privilege database permissions, or isolate tenant workloads.

One common path involves an API endpoint that dynamically constructs SQL queries using string interpolation based on user-controlled parameters. For example, an endpoint accepting a tenant identifier might concatenate it into a SQL statement without proper parameterization or schema isolation. An attacker could supply a tenant ID such as '; SELECT * FROM system.users --, causing the query to break out of the intended data namespace and read from system tables. CockroachDB’s SQL layer will execute the injected fragment if the application does not rigorously validate or parameterize inputs, potentially exposing cluster metadata or configuration details that aid in further exploitation.

Another vector arises from stored procedures or user-defined functions in CockroachDB that are invoked by Axum-based services. If these routines perform filesystem-like operations or call external network functions and are accessible via crafted inputs, an attacker may leverage them to execute arbitrary logic within the database node’s environment. This is particularly relevant when the database is deployed with extended capabilities enabled and the API does not enforce strict input validation or command whitelisting. The escape can pivot from the database to the host when the database process has elevated operating-system privileges or when network policies are permissive.

Deployment configurations amplify the impact. In Kubernetes, a Pod running an Axum service might mount CockroachDB client certificates and keys. If an attacker achieves code execution inside the application container through an injection flaw, they could read these mounted secrets and compromise the database client identity. From there, they might perform privileged operations allowed to that client, such as altering schema or reading from restricted tables. Proper pod security policies, restricted service account permissions, and encrypted secrets reduce the likelihood of lateral movement after an initial injection.

middleBrick’s scans include checks for Input Validation and Property Authorization, which help surface endpoints where untrusted data reaches the database layer without safeguards. The tool also examines authentication and authorization mechanisms across the API to detect BOLA/IDOR patterns that could allow tenant boundary violations. These checks are relevant because a weak authorization model in Axum routes can permit an attacker to submit identifiers that query or modify data belonging to other tenants or system-level objects, effectively enabling a sandbox escape through the database.

Because CockroachDB supports distributed transactions and multi-region deployments, misconfigured isolation levels or overly permissive role bindings can expose administrative operations to API-facing queries. For instance, setting transaction isolation to READ UNCOMMITTED in sensitive workflows may allow reading intermediate states that reveal internal timing or configuration data. An Axum service that does not explicitly set transaction context may inherit these settings, unintentionally aiding an attacker’s reconnaissance for a more severe escape.

Remediation focuses on strict input handling, least-privilege database roles, and explicit transaction controls. In Axum, prefer extracting query parameters into typed structures and using compile-time checks to avoid string-based SQL assembly. When dynamic SQL is unavoidable, use positional placeholders and let the driver manage escaping. The following examples assume the use of tokio-postgres with TLS and a dedicated database user per tenant or service.

1. Parameterized queries with typed extraction

Define a extractor that validates and parses tenant identifiers against an allowlist or a database lookup, then use prepared statements:

use axum::{
    extract::Query,
    response::IntoResponse,
};
use serde::Deserialize;
use tokio_postgres::{NoTls, Client};

#[derive(Deserialize)]
pub struct ReportQuery {
    tenant_id: String,
    report_name: String,
}

async fn get_report(
    Query(params): Query,
    db_client: &Client,
) -> impl IntoResponse {
    // Validate tenant_id format before using it
    if !params.tenant_id.chars().all(|c| c.is_alphanumeric() || c == '-' || c == '_') {
        return (StatusCode::BAD_REQUEST, "invalid tenant identifier");
    }

    // Use positional placeholders; the driver handles quoting
    let rows = db_client
        .query(
            "SELECT title, content FROM tenant_reports WHERE tenant_id = $1 AND name = $2",
            &[¶ms.tenant_id, ¶ms.report_name],
        )
        .await
        .map_err(|e| (StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    // Process rows...
}

2. Least-privilege CockroachDB role setup

Create a dedicated database user for the Axum service and grant only necessary permissions. Avoid public or admin roles. Example SQL executed by an operator:

-- Create a role with read/write only on tenant-specific schema
CREATE ROLE axum_app WITH LOGIN PASSWORD 'strong_password';
GRANT USAGE ON SCHEMA tenant_123 TO axum_app;
GRANT SELECT, INSERT, UPDATE ON ALL TABLES IN SCHEMA tenant_123 TO axum_app;
REVOKE ALL ON DATABASE crdb_internal FROM axum_app;
REVOKE ALL ON SCHEMA pg_catalog FROM axum_app;

In Axum, configure the connection string to use this role and avoid connecting as a superuser. Rotate credentials periodically and store them in a secrets manager mounted securely by the runtime environment.

3. Explicit transaction isolation and context

Set transaction isolation explicitly to prevent unintended reads of uncommitted states. In Axum handlers that interact with CockroachDB, begin transactions with strict isolation:

use tokio_postgres::Transaction;

async fn write_ledger(
    db_client: &Client,
    tenant_id: &str,
    entries: Vec<LedgerEntry>,
) -> Result<(), Box<dyn std::error::Error>> {
    let txn = db_client.transaction().await?;
    txn.execute(
        "SET TRANSACTION ISOLATION LEVEL REPEATABLE READ",
        &[],
    ).await?;

    for entry in entries {
        txn.execute(
            "INSERT INTO ledger (tenant_id, account, delta) VALUES ($1, $2, $3)",
            &[&tenant_id, &entry.account, &entry.delta],
        ).await?;
    }
    txn.commit().await?;
    Ok(())
}

4. Avoid CockroachDB internal exposure

Disable or restrict access to built-in statements and tables that reveal cluster internals. If not needed, prevent usage of SHOW and EXPLAIN through application policies and database role restrictions. Ensure that the Axum service account cannot query crdb_internal or execute administrative commands.

5. Runtime and secret management

Mount CockroachDB client certificates and secrets via Kubernetes secrets or a similar mechanism with read-only access to the application container. Run the Axum service with a non-root user and apply pod security standards to limit filesystem and network access. Combine these runtime hardening steps with network policies that restrict egress to the database endpoints only.