# [Security] Harden Script Execution Endpoint Against Command Injection and Path Traversal Attacks

[prince-pokharna]

Summary

DevShell executes shell scripts through a Flask backend and streams execution output to clients. Based on the repository architecture, script execution workflow, and subprocess-based design, there appears to be a potential risk of command injection and path traversal if user-supplied script identifiers or execution parameters are not strictly validated before being passed to subprocess execution routines.

Since the primary purpose of DevShell is to execute shell scripts, strengthening input validation and execution safeguards would significantly improve the application's security posture.

---

Problem Description

The application exposes functionality that allows users to execute scripts through a web interface and API endpoints.

If script names, arguments, file paths, or remote script URLs are accepted from HTTP requests and subsequently passed to shell commands without strict validation, several attack vectors may become possible:

• Command Injection
• Path Traversal
• Arbitrary File Access
• Unsafe Remote Script Fetching
• Server-Side Request Forgery (SSRF)

Because script execution is a core feature of DevShell, these attack surfaces deserve additional hardening.

---

Potential Attack Scenarios

1. Command Injection Through Script Parameters

If user-controlled input is interpolated into shell commands and executed using:

subprocess.Popen(command, shell=True)

or similar patterns, shell metacharacters may be interpreted by the operating system.

Example payload:

{
  "script": "deploy.sh; echo injected"
}

If concatenated directly into a shell command, unintended commands may execute alongside the intended script.

---

2. Path Traversal via Script Resolution

The project stores scripts within dedicated script directories.

Without strict path validation, a crafted request could attempt to escape the intended directory structure:

{
  "script": "../../app.py"
}

Potential consequences include:

• Accessing unintended files
• Executing unauthorized scripts
• Reading application source files
• Overwriting files in unsafe implementations

---

3. Remote Script Fetching Risks

The README references the ability to pull scripts from GitHub-hosted sources.

If remote URLs are accepted from user input and passed directly to shell utilities such as:

curl <url>
wget <url>

without validation, additional risks may arise:

• SSRF
• Downloading untrusted content
• Unexpected network access
• Potential command injection depending on implementation

---

Steps to Reproduce

1. Clone the repository.
2. Start the application:

python app.py

3. Identify the script execution endpoint (for example /run or equivalent).

4. Submit a crafted request containing shell metacharacters:

curl -X POST http://127.0.0.1:5000/run \
  -H "Content-Type: application/json" \
  -d '{
    "script":"test.sh; echo injected"
  }'

5. Observe whether:

• The request is accepted.
• Additional commands are interpreted.
• Path traversal payloads bypass directory restrictions.
• Remote URLs are accepted without validation.

---

Current Behavior

The current implementation appears to rely on subprocess-based script execution.

It is unclear whether:

• User input is sanitized.
• Shell metacharacters are rejected.
• Path traversal protections are enforced.
• Remote URLs are validated against an allowlist.

Adding explicit safeguards would reduce the risk of future vulnerabilities and improve defense in depth.

---

Expected Behavior

The application should:

• Execute only approved scripts.
• Reject invalid filenames.
• Prevent directory traversal attempts.
• Avoid shell interpretation of user-controlled input.
• Restrict remote downloads to approved domains.
• Return clear validation errors for malformed requests.

---

Proposed Solution

1. Avoid shell=True

Prefer argument-list execution instead of shell command strings.

Unsafe

subprocess.Popen(
    f"bash {script_name}",
    shell=True
)

Safer

subprocess.Popen(
    ["bash", resolved_script_path],
    shell=False
)

This prevents shell metacharacters from being interpreted.

---

2. Enforce Safe Path Resolution

Resolve all script paths relative to a predefined scripts directory.

import os

SCRIPTS_ROOT = os.path.abspath("scripts/linux")

def resolve_safe_path(script_name: str):
    basename = os.path.basename(script_name)

    resolved = os.path.realpath(
        os.path.join(SCRIPTS_ROOT, basename)
    )

    if not resolved.startswith(SCRIPTS_ROOT):
        raise ValueError("Path traversal blocked")

    return resolved

---

3. Add Filename Validation

Restrict filenames to expected patterns.

import re

def validate_script_name(name):
    if not re.match(
        r"^[a-zA-Z0-9_\-\.]+\.sh$",
        name
    ):
        raise ValueError(
            "Invalid script name"
        )

    return name

---

4. Validate Remote URLs

Only permit approved GitHub domains.

from urllib.parse import urlparse

ALLOWED_DOMAINS = {
    "raw.githubusercontent.com",
    "gist.githubusercontent.com"
}

def validate_url(url):
    parsed = urlparse(url)

    return (
        parsed.scheme == "https"
        and parsed.netloc in ALLOWED_DOMAINS
    )

---

5. Add Security Tests

Introduce automated tests covering:

• Command injection payloads
• Path traversal attempts
• Invalid filenames
• Unauthorized remote URLs
• Safe subprocess invocation

This helps prevent regressions in future releases.

---

Benefits

• Reduces command injection risk.
• Prevents directory traversal attacks.
• Improves safety of remote script imports.
• Strengthens deployment security.
• Provides defense-in-depth around the application's most sensitive functionality.

---

Why This Matters

DevShell's core responsibility is executing shell scripts.

Any weakness in input handling around script execution can have a disproportionate impact compared to traditional web applications. Strengthening validation and subprocess safety mechanisms would improve reliability, reduce risk, and make the platform safer for local, shared-network, and self-hosted deployments.

---

Contribution

I would be happy to work on implementing these safeguards and submit a PR with accompanying test coverage.

Suggested Labels

• security
• bug
• hardening
• level:intermediate
• gssoc26

[prince-pokharna]

Hey @siddu-k ,
I have gone through the project deeply by local running and testing and found some major security vulnerability.
Based on my skill-set and issue solving requirements ,I would want to contribute to the issue .

Please assign it to me.