Python Pexpect属性错误。 'NoneType'没有属性'sendline'

Question

使用Pexpect编写脚本以通过ssh连接，但是会引发属性错误。

import pexpect
PROMPT = ['# ', '>>> ', '> ', '\$ ', '~# ']
def send_command(child, cmd):
    child.sendline(cmd)
    child.expect(PROMPT)
    print child.before, child.after
def connect(user, host, password):
    ssh_newkey = 'Are you sure you want to continue connecting (yes/no)?'
    connStr = 'ssh ' + user + '@' + host
    child = pexpect.spawn(connStr)
    ret = child.expect([ssh_newkey, 'password:'])
    if ret == 0:
        print '[-] Error Connecting'
        return
    elif ret == 1:
        child.sendline('yes')
        ret = child.expect('password:')
        if ret == 0:
            print '[-] Error Connecting'
            return
    child.sendline(password)
    child.expect(PROMPT)
    return child
def main():
    host = 'test.rebex.net'
    user = 'demo'
    password = 'password'
    child = connect(user, host, password)
    send_command(child, 'cat /etc/shadow | grep root')
if __name__ == '__main__':
    main()

我遇到以下错误：

[-] Error Connecting
Traceback (most recent call last):
  File "./bruteSSH.py", line 33, in <module>
    main()
  File "./bruteSSH.py", line 31, in main
    send_command(child, 'cat /etc/shadow | grep root')
  File "./bruteSSH.py", line 6, in send_command
    child.sendline(cmd)
AttributeError: 'NoneType' object has no attribute 'sendline'

我认为这与我的子对象为“ NoneType”有关，但我无法确定自己做错了什么。

Answer 1

首先，您在6行上的缩进是错误的。

由于未正确设置子对象并成功连接子对象，因此导致此错误。

如果这正是您的代码，那么问题在于“ child.sendline（）”在函数外部执行，而child是函数“ send_command”内部的局部变量 因此全局子变量尚未定义

Answer 2

您不会在两个条件上返回任何值。那就是您得到None的地方，也是导致错误的原因。参见下面的注释行：

if ret == 0:
    print '[-] Error Connecting'
    return  # THIS WILL CAUSE YOUR ERROR

elif ret == 1:
    child.sendline('yes')
    ret = child.expect('password:')
    if ret == 0:
        print '[-] Error Connecting'
        return  # THIS WILL ALSO CAUSE YOUR ERROR

但是您的逻辑仍然存在缺陷。如果为数组传递期望值，则Expect会返回0或匹配项的索引。在您的代码中，将其传递给数组。因此，返回值为0表示它已成功匹配您的第一个条目-“您确定”条件。如果匹配，则要发送“是”。以下是我认为您想要的更多内容...

import pexpect
PROMPT = ['# ', '>>> ', '> ', '\$ ', '~# ']
def send_command(child, cmd):
    child.sendline(cmd)
    child.expect(PROMPT)
    print child.before, child.after

def connect(user, host, password):
    ssh_newkey = 'Are you sure you want to continue connecting (yes/no)?'
    connStr = 'ssh ' + user + '@' + host
    child = pexpect.spawn(connStr)
    ret = child.expect(['password:', ssh_newkey])
    if ret == 1:
        child.sendline('yes')
        ret = child.expect('password:')
    if ret != 0:
        print '[-] Error Connecting'
        return  # THIS WILL RETURN A NONE SO YOU SHOULD CHECK FOR IT.  SHOULD EXPLICITLY DO A return None TO MAKE IT CLEARER
    child.sendline(password)
    child.expect(PROMPT)
    return child

def main():
    host = 'localhost'
    user = 'demo'
    password = 'password'
    child = connect(user, host, password)
    if child is not None:
        send_command(child, 'cat /etc/shadow | grep root')
    else:
        print "Problem connecting!"

if __name__ == '__main__':
    main()

Answer 3

问题就在您眼前。如“ [*]错误连接”打印语句所示，当您在连接函数中遇到错误时，您什么也不返回。仅当连接成功时，它才会返回子对象，但是当连接失败时，您将返回“空对象”并退出函数。您无法建立成功的连接，因此子对象永远不会返回到主函数中的“子”变量中。 并且您将此相同的“空对象”传递给send_command（），因此不起作用

import sys

def connect(user, host, password):
    ssh_newkey = 'Are you sure you want to continue connecting (yes/no)?'
    connStr = 'ssh ' + user + '@' + host
    child = pexpect.spawn(connStr)
    ret = child.expect([ssh_newkey, 'password:'])
    if ret == 0:
        print '[-] Error Connecting'
        sys.exit()
    elif ret == 1:
        child.sendline('yes')
        ret = child.expect('password:')
        if ret == 0:
            print '[-] Error Connecting'
            sys.exit()
    child.sendline(password)
    child.expect(PROMPT)
    return child

现在，只有连接成功后，您的程序才会继续执行。 也许期望值和密码可能是错误的，总体问题是您无法建立成功的连接