Command Injection in Phoenix with Api Keys

Command Injection in a Phoenix application becomes significantly riskier when API keys are involved because keys are often passed as request parameters, headers, or metadata that flow into system-level operations. If user-influenced data associated with API key handling is concatenated into OS commands, an attacker can inject shell metacharacters to execute arbitrary commands.

Consider a scenario where a Phoenix endpoint accepts an API key and uses it to invoke a system utility, such as a log analyzer or a custom binary, without proper sanitization. For example, a developer might construct a command like cmd = "log_parser --key " <> api_key and pass it to System.cmd/3. If the API key contains characters such as &, ;, or |, the shell interprets them as control operators, leading to command injection. This pattern violates secure input validation practices and maps to the OWASP API Top 10 category of Injection.

In a black-box scan, middleBrick tests this attack surface by submitting API key values that include shell metacharacters and observing whether unintended commands execute. A vulnerable endpoint might reflect injected output or change runtime behavior, indicating that the API key is being used unsafely in command construction. Such findings are reported with severity and remediation guidance, helping you address the issue before it reaches production.

Real-world attack patterns reference known CVEs where command injection was chained with weak handling of identifiers or tokens. For instance, endpoints that construct dynamic commands using external identifiers are prone to exploitation if input validation is bypassed. The presence of API keys does not inherently create the flaw, but their usage context—such as passing them directly to shell utilities—amplifies the impact and likelihood of successful injection.

To remediate command injection risks related to API keys in Phoenix, avoid passing API keys or any user-influenced data directly to shell commands. Instead, use language-native libraries or isolated execution contexts that do not involve a shell interpreter.

Replace System.cmd/3 with safer approaches. For example, if you need to invoke an external binary, use Port with a list of arguments, which bypasses shell parsing entirely:

def safe_parse_log(api_key) do
  # api_key is passed as a separate argument, not interpolated into a shell string
  port = Port.open({:spawn_executable, "log_parser"}, [:binary, args: ["--key", api_key]])
  case Port.command(port, "") do
    {_, {:data, result}} -> result
    _ -> {:error, :execution_failed}
  end
end

If your workflow requires constructing command-like strings, validate and sanitize the API key by allowing only alphanumeric characters and rejecting any characters that have special meaning in shells:

def valid_api_key?(key) when is_binary(key) do
  Regex.match?(~r/^[a-zA-Z0-9\-_]+$/, key)
end

def process_with_key(api_key) do
  if valid_api_key?(api_key) do
    # Use a safe execution path here
    safe_parse_log(api_key)
  else
    {:error, :invalid_api_key}
  end
end

Additionally, store API keys in environment variables or secure vaults rather than accepting them directly from unauthenticated requests. When using configuration, reference them via System.get_env/1 without exposing them in logs or error messages. middleBrick scans help identify whether API key handling flows into unsafe command construction by analyzing runtime behavior alongside OpenAPI specifications, providing prioritized findings with remediation guidance.

For teams using the middleBrick CLI, you can run middlebrick scan <url> to test your endpoints. The Pro plan supports continuous monitoring and CI/CD integration, which can fail builds if unsafe patterns are detected during scans.