Command Injection in Phoenix with Cockroachdb

Command injection occurs when untrusted input is passed to system-level commands without proper validation or escaping. In a Phoenix application using Cockroachdb, this risk can emerge indirectly through misuse of Elixir functions that construct shell commands, often when integrating with tooling, migrations, or custom administrative scripts. While Cockroachdb itself is a database and does not directly execute shell commands, the application layer that interacts with it can become the vector if dynamic query building or external command invocation is not handled safely.

For example, consider a scenario where a developer uses System.cmd/3 to run a Cockroachdb SQL script or a helper binary, passing user-controlled data as part of the command arguments. If input is not sanitized, an attacker may inject additional shell commands using shell metacharacters such as &&, ||, or backticks. This can lead to unauthorized command execution on the host, potentially exposing database credentials or enabling further intrusion. A typical vulnerable pattern might look like:

user_input = "some_table; rm -rf /" # injected
System.cmd("cockroach", ["sql", "--execute=" <> user_input], [])

In this contrived case, the injected semicolon allows a second command to run. Even if the primary intent is to pass SQL to Cockroachdb, unsafe construction of the command line bypasses the intended database operation. The risk is compounded when the Phoenix app runs with elevated privileges or when the database connection string is derived from environment variables that could be manipulated via command injection.

Another subtle vector involves log aggregation or observability tooling. If Phoenix callbacks or custom tasks construct command-line strings for external logging processors and include raw request data, an attacker may manipulate the command line to exfiltrate data or alter behavior. Because Cockroachdb is often used in distributed and cloud-native environments, the exposed host running Phoenix may also host orchestration tools, increasing the blast radius of a successful injection.

Importantly, middleBrick detects such issues during black-box scanning by analyzing runtime behavior and OpenAPI specifications, even when the vulnerability arises from unsafe interaction patterns rather than the database itself. The scanner does not make assumptions about internal architecture but flags risky endpoint designs that could permit command injection through indirect paths involving Cockroachdb-dependent workflows.

Secure remediation centers on avoiding shell command construction altogether and using structured, parameterized approaches. When interacting with Cockroachdb, prefer the built-in Ecto query interface and parameterized queries to prevent injection at the database layer. For cases where external commands are unavoidable, strictly validate and sanitize inputs, and avoid passing untrusted data directly into command arguments.

Below are concrete, safe examples of working with Cockroachdb in Phoenix.

Safe Ecto Query with Parameterized Inputs

Use Ecto's query syntax to ensure values are never interpreted as executable code:

query = from(u in User, where: u.id == ^user_id and u.status == ^status)
Repo.all(query)

This approach guarantees that user_id and status are bound as parameters, not string-concatenated into SQL.

Using Ecto.Adapters.SQL for Raw SQL (When Necessary)

If raw SQL is required, use parameterized statements via Ecto.Adapters.SQL.query/3:

result = Ecto.Adapters.SQL.query!(Repo, "SELECT * FROM users WHERE id = $1 AND email = $2", [user_id, email])
# For Cockroachdb, use $1, $2 style placeholders

This ensures that inputs are properly escaped by the driver and not interpreted as shell commands.

Avoiding Unsafe System Command Construction

If you must invoke external binaries, validate and whitelist inputs rigorously. Never concatenate user input into command arguments:

# Unsafe — do not use
System.cmd("cockroach", ["sql", "--execute=SELECT * FROM #{table_name}"])

# Safer: whitelist table names and use parameterized execution
allowed_tables = ["users", "orders", "products"]
table_name = if table_name in allowed_tables, do: table_name, else: raise "Invalid table"
# Prefer structured operations over shell commands entirely

For administrative tasks, consider using Cockroachdb's HTTP status endpoints or built-in tooling that does not require shell invocation.

middleBrick's scanning capabilities include checks related to unsafe consumption patterns and input validation, which can highlight endpoints where command injection risks intersect with API surface areas. By combining secure coding practices with continuous scanning, teams can reduce the likelihood of injection vulnerabilities in Phoenix applications backed by Cockroachdb.