TypeError: a bytes-like object is required, not 'str' when reading and iterating over a file in Python3.x

Question

I'm trying to read and iterate over a text file in Python but I keep running into this error. I'm pretty new to Python and I'm not sure where the error in my code is:

import socket

def getBanner(ip, port):
    try:
        socket.setdefaulttimeout(2)
        s = socket.socket()
        s.connect((ip, port))
        banner = s.recv(1024)
        return banner
    except:
        return

def vulnCheck(banner):
    f = open("vuln_banners.txt", 'r')
    for line in f.readlines():
        if line.strip('\n') in banner:
            print("[+] Server is vulnerable: "+banner.strip('\n'))
        else:
            print("[-] FTP Server is not vulnerable.")
            return


def main():
    portList = [21, 22, 25, 80, 110, 443]
    for x in range(1, 255):
        ip = '192.168.1.' + str(x)
        for port in portList:
            banner = getBanner(ip, port)
            if banner:
                print("[+] " + str(ip) + ": " + str(banner))
                vulnCheck(banner)

if __name__ == '__main__':
    main()

I would like my program to iterate over a list of strings in a text file to compare against a banner, however, every time I run the code I get this error:

  File "/home/testing/Documents/HelloWorld.py", line 17, in vulnCheck
    if line.strip('\n') in banner:
TypeError: a bytes-like object is required, not 'str'

I've read few of the answers about this error and they talk about NOT opening the file as binary, but I don't think I'm doing that in my code. I'm simply trying to read each line in a text file and iterate over it. Can anyone point out the error in my code? Any help would be appreciated.

Answer 1

In getBanner , banner = s.recv(1024) is a bytes object, so banner in vulnCheck is also bytes . Since you did not open the file in binary mode, line.strip('\\n') will be a string . It is an error to search for str ings in bytes because a string must be encoded in order to do this (or the bytes must be decoded appropriately).

Thus, you should indeed open the file in binary mode.

Answer 2

横幅对象不是字符串，因此python无法搜索字节对象，试图找到字符串。

Answer 3

Your socket returns bytes while the file contains strings. You need to map one to the other - probably decode bytes banners to strings.

As an aside, repeatedly reading the same static text file is a significant bottleneck here. Unless the file is so huge that you should be using a database instead anyway, read it once, at the start.

The following also has assorted bug fixes and stylistic updates; most importantly, don't return in the middle of the vulnerability check if the first vulerability wasn't matched. Notice also how functions generally just return a result, and leave it to the caller to decide eg whether to print something based on that.

import socket

def get_banner(ip, port):
    try:
        socket.setdefaulttimeout(2)
        s = socket.socket()
        s.connect((ip, port))
        banner = s.recv(1024)
        return banner.decode('utf-8')
    except:
        return

def vuln_check(banner, vulnlist):
    for line in vulnlist:
        if line in banner:
            return True
    return False

def read_vulns(filename):
    with open(filename, 'r') as f:
        return f.read().splitlines()

def main():
    vulns = read_vulns("vuln_banners.txt")

    port_list = [21, 22, 25, 80, 110, 443]
    for x in range(1, 255):
        ip = '192.168.1.' + str(x)
        for port in port_list:
            banner = get_banner(ip, port)
            if banner:
                print("[+]", ip + ":", banner)
                if vuln_check(banner, vulns):
                    print("[+] Server is vulnerable:", banner.strip('\n'))
                else:
                    print("[-] FTP Server is not vulnerable.")

if __name__ == '__main__':
    main()