system: You are an expert security code reviewer. You will be shown a source code file along with a multi-select question listing several CWE (Common Weakness Enumeration) categories. Your task is to identify which of the listed CWEs are present in the code.

OUTPUT FORMAT: Respond with the letter(s) of all correct options, sorted alphabetically and comma-separated, wrapped in a single \boxed{...}. Examples: `\boxed{A}` for one correct, `\boxed{A,C}` for two, `\boxed{A,C,E}` for three. Output the boxed answer ONLY -- no explanation, no other text.

user: ```python
from __future__ import print_function
import datetime
import pickle
import time
import os.path
from googleapiclient.discovery import build
from google_auth_oauthlib.flow import InstalledAppFlow
from google.auth.transport.requests import Request
import webbrowser
import re

# If modifying these scopes, delete the file token.pickle.
SCOPES = ['https://www.googleapis.com/auth/calendar.readonly']

link_save = []
sleep_time = 300


def find_url(string): 
    # findall() has been used  
    # with valid conditions for urls in string
    url = re.findall('http[s]?://(?:[a-zA-Z]|[0-9]|[$-_@.&+]|[!*\(\), ]|(?:%[0-9a-fA-F][0-9a-fA-F]))+', string)
    return url 

def get_event(creds, service):

    #DOESN'T WORK WITHOUT THIS
    now = datetime.datetime.utcnow().isoformat() + 'Z' # 'Z' indicates UTC time

    nowist = datetime.datetime.now()

    #GETTING THE UPCOMING EVENT
    events_result = service.events().list(calendarId='primary', timeMin=now,
                                        maxResults=1, singleEvents=True,
                                        orderBy='startTime').execute()
    events = events_result.get('items', [])

    if not events:
        print('No upcoming events found.')
        exit()
        
    start = events[0]['start'].get('dateTime', events[0]['start'].get('date'))
    time = start[:16]

    #FOR FULL DAY EVENTS
    if(start[17:]==""):
        print("Next event is a full day event")
        return 0
    
    record_time = datetime.datetime.strptime(time, '%Y-%m-%dT%H:%M')

    if(nowist.month<record_time.month):
        print("Next event is not this month")
        return 0

    #if(nowist.day<record_time.day):
     #   print("Next event is not today")
      #  return 0

    print("Found Event happening today!")


    rec_timeVal = int(str(record_time.hour)+str(record_time.minute))
    now_timeVal = int(str(nowist.hour)+str(nowist.minute))
     
    #print("rec_timeVal: ", rec_timeVal)
    print("Current Time:", nowist)
    print("Next Event Time:", record_time)

    if(nowist.hour==record_time.hour):
        if(nowist.minute>=record_time.minute-5 and nowist.minute<=record_time.minute+10):
            print("Event time matches current time! LAUNCHING...")
            try:
                zoom_url = events[0]['description']
                zoom_url = find_url(zoom_url)
                print("Searching for URL: ",zoom_url)
                if(zoom_url==""):
                    print("No URL found in description")
                    return 0
                if zoom_url not in link_save:
                    link_save.append(zoom_url)
                    webbrowser.open_new_tab(zoom_url[0])
                else:
                    print("Meeting already launched, waiting for next meeting")
                return 0
            except:
                print("URL does not exist")
                return 0
        
    
    print("NEXT EVENT: ", record_time, events[0]['summary'])

    return 0
    

    


def main():

    try:
    
        #AUTHENTICATION START--------------------------------------------------------------------------------
        
        creds = None
        # The file token.pickle stores the user's access and refresh tokens, and is
        # created automatically when the authorization flow completes for the first
        # time.
        if os.path.exists('token.pickle'):
            with open('token.pickle', 'rb') as token:
                creds = pickle.load(token)
        # If there are no (valid) credentials available, let the user log in.
        if not creds or not creds.valid:
            if creds and creds.expired and creds.refresh_token:
                creds.refresh(Request())
            else:
                flow = InstalledAppFlow.from_client_secrets_file(
                    'credentials.json', SCOPES)
                creds = flow.run_local_server(port=0)
            # Save the credentials for the next run
            with open('token.pickle', 'wb') as token:
                pickle.dump(creds, token)
                
        #AUTHENTICATION END------------------------------------------------------------------------------

        service = build('calendar', 'v3', credentials=creds)

        while(get_event(creds, service)!=1):
            #HOW LONG TO SLEEP FOR IN SECONDS
            time.sleep(sleep_time)

    except:
        print("Please check your internet connection")
        time.sleep(sleep_time)
        main()    

if __name__ == '__main__':
    main()

```

Which of the following CWE vulnerability categories are present in this code? Multiple options may be correct.

  A) CWE-20: Improper Input Validation
  B) CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
  C) CWE-1333: Inefficient Regular Expression Complexity
  D) CWE-918: Server-Side Request Forgery (SSRF)
  E) CWE-730: OWASP Top Ten 2004 Category A9 - Denial of Service
  F) CWE-209: Generation of Error Message Containing Sensitive Information
Answer: A