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+#!/usr/bin/env python3
+
+# Ndiff
+#
+# This programs reads two Nmap XML files and displays a list of their
+# differences.
+#
+# Copyright 2021 Nmap Software LLC
+# Ndiff is distributed under the same license as Nmap. See the file
+# LICENSE in the Nmap source distribution or
+# https://nmap.org/book/man-legal.html for more details.
+#
+# Original author was David Fifield based on a design by Michael Pattrick
+
+import sys
+
+# Check if the given directory, and all its parent directories, are owned and
+# writable only by our euid or by root. If symlinks are present, they are
+# recursively checked, up to a limit of SYMLINK_LIMIT.
+# https://www.securecoding.cert.org/confluence/display/seccode/FIO15-C.+Ensure+that+file+operations+are+performed+in+a+secure+directory
+# We use this code for Zenmap too
+SYMLINK_LIMIT = 5
+def is_secure_dir(path, num_symlinks=0):
+    import os
+    import os.path
+    import stat
+
+    if not os.path.isabs(path):
+        return False
+
+    if num_symlinks >= SYMLINK_LIMIT:
+        return False
+
+    dirs = []
+    while True:
+        dirs.append(path)
+        dirname = os.path.dirname(path)
+        if dirname == path:
+            break
+        path = dirname
+    # Traverse root-to-leaf.
+    dirs.reverse()
+
+    for dir in dirs:
+        if os.path.islink(dir):
+            link = os.readlink(dir)
+            if not is_secure_dir(link, num_symlinks + 1):
+                return False
+            continue
+        if not os.path.isdir(dir):
+            return False
+        buf = os.stat(dir)
+        if buf.st_uid != os.geteuid() and buf.st_uid != 0:
+            return False
+        if buf.st_mode & (stat.S_IWGRP | stat.S_IWOTH) != 0:
+            return False
+
+    return True
+
+# Add the install_lib directory to sys.path, the list of directories searched
+# for modules, but don't do it if the directory or its parents may be writable
+# by other users. The following line is replaced by the installation program.
+INSTALL_LIB = None
+if INSTALL_LIB is not None and is_secure_dir(INSTALL_LIB):
+    sys.path.append(INSTALL_LIB) # lgtm[py/unreachable-statement]
+
+try:
+    import ndiff
+except ImportError as e:
+    print("""\
+Could not import the ndiff module: %s.
+I checked in these directories:""" % repr(e), file=sys.stderr)
+    for dir in sys.path:
+        print("    %s" % dir, file=sys.stderr)
+    print("""\
+If you installed Ndiff in another directory, you may have to add the
+modules directory to the PYTHONPATH environment variable.""", file=sys.stderr)
+    sys.exit(1)
+
+import ndiff
+
+if __name__ == "__main__":
+    sys.excepthook = ndiff.excepthook
+    sys.exit(ndiff.main())