system: You are an expert security code reviewer. You will be shown a source code file along with a catalog of candidate CWE (Common Weakness Enumeration) categories with their official MITRE names. Your task is to list every distinct CWE from that catalog that is actually present in the code. The catalog is comprehensive for this dataset -- the answer is a (possibly small) subset of it.

OUTPUT FORMAT: Respond with a comma-separated list of CWE IDs in the form `CWE-N`, sorted in ascending numeric order, wrapped in a single \boxed{...}. Examples: `\boxed{CWE-79}` for one, `\boxed{CWE-22,CWE-79,CWE-327}` for three. Output the boxed answer ONLY -- no explanation, no other text.

user: ```python
""" Transformation operations working on MPTs or BMPT words.

"""

import re
from collections import OrderedDict

from mptpy.node import Node


def word_to_nodes(word, idx=0):
    """ Translate an MPT in the BMPT language (see Purdy & Batchelder 2009) to
    a binary tree

    Parameters
    ----------
    word : MPTWord
        MPT in the BMPT language format

    Returns
    -------
    Node
        root node of the MPT

    """

    node = Node(word[idx])

    if not word.is_leaf(word[idx]):
        node.pos = word_to_nodes(word, idx=idx + 1)
        node.neg = word_to_nodes(word, idx=idx + 1 + len(node.pos))

    return node

def to_easy(mpt):
    """ Transforms the MPT to the easy format

    Parameters
    ----------
    mpt : MPT
        MPT model

    Returns
    -------
    str
        tree in the easy format

    """

    lines = get_formulae(mpt)

    easy = ""
    for key in sorted(lines.keys()):
        line = " + ".join(lines[key]) + "\n"
        easy += line
    return easy

def easy_to_bmpt(lines, sep=' ', leaf_step=0):
    """ Turns the lines of a tree in the easy file format
    to a tree in the formal language

    Parameters
    ----------
    lines : list
        list of lines of the file in the easy format
    sep : str
        separator
    leaf_step : int

    Returns
    -------
    str
        Tree in Formal language form, with sep as separator

    """

    tree = dict()
    for i, line in enumerate(lines):
        leaf_name = i + leaf_step
        line = line.replace(" ", "").strip()
        tree[leaf_name] = line.split("+")

    for answer in tree.items():
        for i, branch in enumerate(answer[1]):
            answer[1][i] = branch.split("*")

    tree_str = dict_to_bmpt(tree, sep=sep)

    return tree_str

def dict_to_bmpt(tree, sep=" "):
    """ Turns a dictionary of answers and corresponding branches
    to a tree in the formal language

    Parameters
    ----------
    tree : dict
        answers and corresponding branches

    Returns
    -------
    str
        Tree in Formal language form, with " " as separator

    """

    if len(tree.keys()) == 1 and list(tree.items())[0][1] == [[]] :
        return str(list(tree.keys())[0])

    # match the parameters : letter(s) + optional number
    root = re.search(r"[A-z_]+\d*", list(tree.values())[0][0][0]).group()

    pos_tree, neg_tree = split_tree(tree)

    res= sep.join([root, dict_to_bmpt(pos_tree), dict_to_bmpt(neg_tree)])

    return res

def split_tree(tree):
    """ Splits the dictionary of answers and corresponding branches
    to the positive and the negative subtrees

    Parameters
    ----------
    tree : dict
        answers and corresponding branches

    Returns
    -------
    tuple
        positive subtree, negative subtree

    """

    neg_tree = dict()
    pos_tree = dict()

    for answer in tree.items():
        for branch in answer[1]:
            subtree = pos_tree if '1-' not in branch[0] else neg_tree

            if answer[0] not in subtree.keys():
                subtree[answer[0]] = []
            subtree[answer[0]].append(branch[1:])

    return pos_tree, neg_tree

def get_formulae(mpt):
    """ Builds a dictionary of the answers and the
    respective branch formulas

    Parameters
    ----------
    mpt : MPT

    Returns
    -------
    dict(int, string)
        Dictionary of the answer categories of the tree and the branch formulas

    """
    lines = {answer : [] for answer in mpt.word.answers}
    def recursive_to_formulae(node, temp=""):
        """ Recursively compute the branch formulae

        """

        if node.leaf:
            lines[node.content] += [temp]
            return None

        left_mult = "" if node.pos.leaf else " * "
        right_mult = "" if node.neg.leaf else " * "

        recursive_to_formulae(node.pos, temp +
                              node.content + left_mult)
        recursive_to_formulae(node.neg, temp +
                              "(1-" + node.content + ")" + right_mult)

        return lines

    formulae = recursive_to_formulae(mpt.root)
    ordered = OrderedDict()
    for key in sorted(formulae, key=int):
        ordered[key] = formulae[key]

    return ordered

```

Candidate CWE catalog (every CWE that appears anywhere in this dataset):
  - CWE-20: Improper Input Validation
  - CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
  - CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
  - CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
  - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
  - CWE-89: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injection')
  - CWE-94: Improper Control of Generation of Code ('Code Injection')
  - CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
  - CWE-116: Improper Encoding or Escaping of Output
  - CWE-117: Improper Output Neutralization for Logs
  - CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
  - CWE-209: Generation of Error Message Containing Sensitive Information
  - CWE-215: Insertion of Sensitive Information Into Debugging Code
  - CWE-295: Improper Certificate Validation
  - CWE-312: Cleartext Storage of Sensitive Information
  - CWE-326: Inadequate Encryption Strength
  - CWE-327: Use of a Broken or Risky Cryptographic Algorithm
  - CWE-377: Insecure Temporary File
  - CWE-502: Deserialization of Untrusted Data
  - CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
  - CWE-611: Improper Restriction of XML External Entity Reference
  - CWE-614: Sensitive Cookie in HTTPS Session Without 'Secure' Attribute
  - CWE-643: Improper Neutralization of Data within XPath Expressions ('XPath Injection')
  - CWE-730: OWASP Top Ten 2004 Category A9 - Denial of Service
  - CWE-732: Incorrect Permission Assignment for Critical Resource
  - CWE-776: Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
  - CWE-918: Server-Side Request Forgery (SSRF)
  - CWE-943: Improper Neutralization of Special Elements in Data Query Logic
  - CWE-1004: Sensitive Cookie Without 'HttpOnly' Flag
  - CWE-1333: Inefficient Regular Expression Complexity

List every distinct CWE from the catalog above that is actually present in this code.
Answer: CWE-20