Base64encode bytes-like object is required in python3

Question

My code is:

_cmd = "|| echo " + base64.b64encode(args.cmd) + "|base64 -d|bash"
   p.update({"form_284": _cmd})

My error is:

Traceback (most recent call last):
  File "openemr_rce.py", line 136, in <module>
    _cmd = "|| echo " + base64.b64encode(args.cmd) + "|base64 -d|bash"
  File "/usr/lib/python3.8/base64.py", line 58, in b64encode
    encoded = binascii.b2a_base64(s, newline=False)
TypeError: a bytes-like object is required, not 'str'

Edit:

There is no problem when you run it in python2

args.cmd is a str, it should be a bytes object to make it compatible with base 64 encoding. Without knowing where it came from, we can't know why it's the wrong type. A minimal reproducible example is needed for a complete answer. — ShadowRanger
– ShadowRanger, Commented Sep 10, 2020 at 22:08
Heh. I wonder if you're playing the same CTF where I recently saw OpenEMR used as a target... — Charles Duffy
– Charles Duffy, Commented Sep 10, 2020 at 22:14

Bharel · Accepted Answer · 2020-09-10 22:41:36Z

2

Your args.cmd is a string.

If it was meant to be, try base64.b64encode(args.cmd.encode("ascii")).decode("ascii").

If your command contains non-ascii characters, the bash cmd is on a system-dependent encoding, and you can use sys.getdefaultencoding() to fetch it.

edited Sep 10, 2020 at 22:41

answered Sep 10, 2020 at 22:08

Bharel

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5 Comments

Bharel Over a year ago

@CharlesDuffy I'm not encoding the base64, I'm encoding the input to the base64 which can be anything.

Bharel Over a year ago

@vortext what do you mean? What was wrong with the solution?

vortext Over a year ago

Traceback (most recent call last): File "openemr_rce.py", line 136, in <module> _cmd = "|| echo " + base64.b64encode(args.cmd.encode("ascii")) + "|base64 -d|bash" TypeError: can only concatenate str (not "bytes") to str

Bharel Over a year ago

If the solution helped you, you can choose to accept the answer by clicking the green check mark next to the answer. For more info, see the help manuals

Bharel Over a year ago

@vortext Indeed, you need to decode the answer as well. Updated appropriately.

Code-Apprentice · Accepted Answer · 2020-09-10 22:09:18Z

0

As the error says, you must pass a "bytes-like object" to b64encode, not a string. To get bytes from a string, you can call encode():

base64.b64encode(args.cmd.encode('utf8'))

answered Sep 10, 2020 at 22:09

Code-Apprentice

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2 Comments

vortext Over a year ago

Traceback (most recent call last): File "openemr_rce.py", line 136, in <module> _cmd = "|| echo " + base64.b64encode(args.cmd.encode('utf8')) + "|base64 -d|bash" TypeError: can only concatenate str (not "bytes") to str

Code-Apprentice Over a year ago

@vortext Please post a new question with your current code. Hint: the problem is very similar. You need to match the correct types.

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