How to Use Run Arguments in Scripts and Command-Line Tools

Secure Handling of Run Arguments: Avoiding Injection and LeaksRun arguments (also called command-line arguments, runtime parameters, or flags) let users and systems modify program behavior without changing code. They are convenient and powerful — and when handled incorrectly, they become a common vector for security problems such as injection attacks, information leaks, privilege escalation, and accidental misconfiguration. This article explains risks associated with run arguments, shows defensive programming patterns, and offers practical checklists and examples for several common platforms and languages.

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Why run-argument security matters

• Run arguments are often treated as trusted because they come from administrators, scripts, or automation; this trust can be misplaced.
• Many attacks exploit unsanitized arguments to execute shell commands, alter program flow, or exfiltrate secrets.
• Leaked arguments appear in process listings, logs, crash reports, and monitoring systems, exposing sensitive data such as API keys, credentials, or personally identifiable information (PII).
• Automated systems (CI/CD, schedulers, container orchestrators) frequently inject arguments, so mistakes can scale broadly across infrastructure.

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Common threats

• Injection: Passing malicious input that is interpreted as code or commands — e.g., shell injection when program builds a command string using an argument.
• Argument spoofing: An attacker with local access launching a process with crafted args to bypass checks or trigger dangerous modes.
• Sensitive-data exposure: Secrets passed as arguments show in ps/top, /proc//cmdline (Linux), crash dumps, audit logs, or external monitoring.
• Environment manipulation: Arguments used to select config files or feature flags can cause the program to load unsafe resources.
• Privilege escalation: Arguments that trigger privileged operations without adequate authorization checks can be abused.

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Principles for secure handling

• Validate and sanitize: Treat all run arguments as untrusted. Enforce strict validation (whitelists, types, length).
• Avoid shell interpretation: Never pass untrusted arguments into shell commands. Use APIs that accept argument lists instead of constructing command lines.
• Don’t pass secrets as args: Prefer environment variables, secure vaults, or configuration files with restricted permissions rather than command-line arguments.
• Limit exposure: Mask or redact sensitive values when logging; minimize argument retention in crash reports and diagnostics.
• Principle of least privilege: Ensure the program’s effective privileges are minimized and that certain dangerous modes require explicit, authenticated approval.
• Fail safe: On invalid or suspicious arguments, prefer failing closed (refuse to run) instead of proceeding in an unsafe state.
• Auditing and monitoring: Track unusual argument patterns, repeated failures, or anomalous flag use.

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Input validation patterns

1. Whitelisting over blacklisting
   • Accept only known allowed values (e.g., “start”, “stop”, “status”) rather than trying to block bad characters.
2. Typed parsing
   • Use library-provided parsers that produce typed values (integers, enums, booleans) rather than manual string parsing.
3. Length and character limits
   • Enforce maximum lengths and restrict characters (e.g., alphanumerics, dashes) for names or IDs.
4. Semantic checks
   • Validate that file paths point inside allowed directories, ports are within valid ranges, and URIs have expected schemes.
5. Rate limiting / throttling
   • For services exposed to users, limit how often certain dangerous flags or operations can be requested.

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Avoiding shell injection

A frequent mistake: building a command string by concatenating arguments and running it through a shell. Example (unsafe):

# DO NOT use: vulnerable to shell injection system(sprintf("tar -czf %s %s", archive_name, user_path)); 

Secure alternatives:

• Use process-spawning APIs that accept an argument array, avoiding shell parsing:
  • Python: subprocess.run([ “tar”, “-czf”, archive_name, user_path ], check=True)
  • Go: exec.Command(“tar”, “-czf”, archiveName, userPath)
  • Node.js: child_process.spawn(“tar”, [“-czf”, archiveName, userPath])
• If you must use a shell, strictly validate and escape arguments (last resort).

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Secrets: never as command-line args

Problems with secrets on command-line:

• Visible in process listings (ps, top), accessible to other local users.
• Stored in shell history if typed interactively.
• Leak into logging, monitoring, and crash dumps.

Safer options:

• Environment variables (with care): processes inherit env vars and they are less visible in casual process listings, but still can be exposed via /proc//environ on Linux or intentional dumps. Use for short-lived secrets and limit access.
• Files with strict permissions: write secret to a file in a secured directory that only the running user can read, then pass only the file path as an argument.
• Secret managers / vaults: retrieve secrets at runtime using secure APIs or agents (HashiCorp Vault, AWS Secrets Manager, GCP Secret Manager) and keep them in memory.
• OS-specific secure storage: keychains or credential stores.

If you must accept secret-like arguments:

• Detect and warn (or reject) patterns that look like secrets.
• Immediately overwrite in-memory buffers after use.
• Do not log them and redact them in diagnostics.

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Logging and diagnostics: redact and minimize

• Never log raw arguments containing potential secrets. Build a redact table (e.g., keys like “token”, “password”) and mask values before logging.
• When producing error reports or telemetry, avoid including full command-line. Log only non-sensitive flags or a sanitized summary.
• For debugging, provide a secure “debug mode” that writes more detail only to accessible local logs and requires explicit opt-in.

Example redaction function (pseudocode):

def redact_args(args):     redacted = []     for k, v in args.items():         if k.lower() in ("password","token","secret","apikey"):             redacted.append((k, "REDACTED"))         else:             redacted.append((k, v))     return redacted 

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Platform-specific guidance

Linux/Unix:

• ps and /proc expose command lines. Avoid secrets as args. Use setuid precautions; sanitize input before dropping privileges.
• When writing daemons, consider using systemd environment files or socket activation rather than long command-line secrets.

Windows:

• Command-line arguments are visible through Process Explorer and APIs. Use secure string APIs (e.g., SecureString) where applicable and avoid passing credentials on the command line.
• For services, use the Windows Credential Manager or service-specific secure mechanisms.

Containers and orchestration:

• Do not bake secrets into container images or declare them as literal args in container manifests. Use orchestrator secret mechanisms (Kubernetes Secrets, Docker secrets) and mount secrets as files or environment variables via secure channels.
• Be cautious with kubectl and container runtime commands that can reveal args in pod specs, audit logs, or cluster events.

Cloud CI/CD:

• Mask secrets in build logs; many CI systems offer built-in secret handling. Do not echo variables to console or pass them as CLI args in job steps that get recorded.

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Access control and authorization for dangerous flags

• Treat certain flags as requiring higher privilege or explicit authorization (e.g., –enable-root-ops, –restore-db).
• Implement an allowlist for which users/services can pass those flags (check process owner, call origin, or an authorization token).
• For remote APIs that accept operational flags, combine flag parsing with authentication and audit logging.

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Examples: secure patterns by language

• Python

  • Use argparse / click for typed parsing and choices.
  • Use subprocess.run with a list to avoid shell=True.
  • Example: argparse ArgumentParser(…).add_argument(“–mode”, choices=[“prod”,“dev”])

• Go

  • Use flag package for typed flags.
  • Use exec.Command with arguments slice.
  • Validate input early in main() and exit if malicious.

• Node.js

  • Use yargs or commander for parsing and validation.
  • Use child_process.spawn with args array; avoid exec() for untrusted inputs.

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Testing and CI checks

• Fuzz arguments: include malformed, overly long, or malicious-looking args in tests.
• Static analysis: scan code for unsafe patterns (use of system(), shell=True, string concatenation into commands).
• Automated secret detection: run tools that detect secrets in code, config, and CI logs.
• Pen testing: include argument-based attack scenarios (injection, local privilege escalation) in threat models.

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Recovery and incident response

• If an argument-related leak is discovered, rotate affected secrets immediately and invalidate any impacted credentials.
• Review logs and audit trails to determine if arguments were misused.
• Patch code to refuse secrets on the command line and improve sanitization; add tests to prevent regression.

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Practical checklist (short)

• Do not pass secrets as run arguments. Prefer vaults or files with restricted perms.
• Use typed parsers and whitelists.
• Avoid shell invocation; use argument arrays.
• Redact sensitive args in logs and telemetry.
• Limit dangerous flags with authorization checks.
• Test with fuzzing and CI scans for unsafe patterns.
• Rotate secrets and audit on any suspected leak.

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Secure handling of run arguments is a mix of engineering discipline, defensive coding, and platform-aware operation. Treat all arguments as untrusted, minimize exposure, and choose safer alternatives for secret transport. These steps reduce attack surface from a common but often-overlooked source of risk.