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
# -*- coding: utf-8 -*-
"""
Created on Sat Dec 22 12:12:53 2018

@author: logesh
"""
#import statements
import pandas as pd
import numpy as np
import re
import nltk
from nltk.corpus import stopwords
from nltk.stem import WordNetLemmatizer
import unicodedata
from pattern.en import suggest
import contractions
pattern = re.compile(r"(.)\1{2,}")
tokenizer = nltk.TweetTokenizer(strip_handles=True)
stopword_list = nltk.corpus.stopwords.words('english')
#url and hyperlinks removal
def remove_url(doc):
    doc = re.sub(r'https?:\/\/.*[\r\n]*','',doc)
    doc = doc.lower()
    return doc
        
#remove special characters
def remove_special_characters(text):
    text = re.sub('[^a-zA-z\s]', '', text)
    return text

#tokenization
def tokenize_text(doc):
    tokens=tokenizer.tokenize(doc)
    filtered_tokens = [token for token in tokens if token not in stopword_list]
    return(" ".join(filtered_tokens))   

#Remove additional characters    
def reduce_lengthening(text):
    return pattern.sub(r"\1\1", text)
        
#remove accented characters
def remove_accented_chars(text):
    text = unicodedata.normalize('NFKD', text).encode('ascii', 'ignore').decode('utf-8', 'ignore')
    return text
  
#lemmentization
def lemmetize(text):
    lem = WordNetLemmatizer()
    tokens = text.split(" ")
    list1 = [lem.lemmatize(token,pos='v') for token in tokens]
    return(" ".join(list1))
   
#Replace contractions in string of text    
def replace_contractions(text):
    return(contractions.fix(text)) 

    


def normalize(sentences):
    count=0
    nor_sentences = []
    for doc in sentences:
        doc = remove_url(doc)
        doc = replace_contractions(doc)
        doc = tokenize_text(doc)
        doc = remove_special_characters(doc)
        doc = remove_accented_chars(doc)
        doc = reduce_lengthening(doc)
        doc = lemmetize(doc)
        doc = re.sub(' +', ' ', doc)
        nor_sentences.append(doc)
        count = count+1
        print(count) 
    return(nor_sentences)    
        
        
```

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