[issue43949] binascii.Error raised in smtplib when initial_response_ok=False

[junpengruan]

junpengruan <632077...@qq.com> added the comment:

Hi Pandu, thanks for your reply!
I have read the RFC4954 you mentioned and agree that the server shouldn't react 
like this. Then I notice that this RFC's publication date is 2007 and the 
server I use is published in 2003, that's maybe the reson why I meet this 
problem, Maybe I should just evade this problem for my own program and close 
this bug?

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[issue43949] binascii.Error raised in smtplib when initial_response_ok=False

[Pandu E POLUAN]

Pandu E POLUAN  added the comment:

> I am using Magic Winmail Server2.4(build 0530) as a SMTP server, which 
> appears dont support initial_response, so I set initial_response_ok=False and 
> got this Error. currently I catch this error and ignore it to evade program 
> failed, it works fine. Is there better way to fix this problem?

I suggest either of:

(1) Contacting the makers of the software, to force Base64-encoding for "334 " 
replies, or

(2) If the text following "334 " is customizable, Base64-encode them yourself, 
then use the base64-encoded text as the customized "334 " response.

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[issue43949] binascii.Error raised in smtplib when initial_response_ok=False

[Pandu E POLUAN]

Pandu E POLUAN  added the comment:

A stronger case is the "Formal Syntax" on 
https://tools.ietf.org/html/rfc4954#page-13 :

>   continue-req= "334" SP [base64] CRLF
> ;; Intermediate response to the AUTH
> ;; command.
> ;; This non-terminal complies with
> ;; syntax defined by Reply-line [SMTP].

Nothing else besides base64 is allowed; after "334 " it MUST be either  
or .

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[issue43949] binascii.Error raised in smtplib when initial_response_ok=False

[Pandu E POLUAN]

Pandu E POLUAN  added the comment:

Technically, that is not the fault of smtplib.SMTP

The standard for SMTP AUTH specifies that characters following "334 " MUST be 
Base64 encoded.

See https://tools.ietf.org/html/rfc4954#page-4 , 3rd paragraph:

> A server challenge is sent as a 334 reply with the text part
> containing the [BASE64] encoded string supplied by the SASL
> mechanism.  This challenge MUST NOT contain any text other
> than the BASE64 encoded challenge.

Servers that send non-BASE64-encoded text after "334 " IMO is violating the 
standards.

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nosy: +pepoluan

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[issue43949] binascii.Error raised in smtplib when initial_response_ok=False

[junpengruan]

New submission from junpengruan <632077...@qq.com>:

Hi
I think there is a bug when initial_response_ok=False and using AUTH PLAIN, the 
server will response like:
--
C: AUTH PLAIN
S: 334 ok. go on
--
and it's not base64 encoding, while in the auth() it will base64 decode the 
resp(here is "ok, go on") which will cause a binascii.Error:

Traceback (most recent call last):
  File "/usr/lib/python3.6/smtplib.py", line 644, in auth
challenge = base64.decodebytes(resp)
  File "/usr/lib/python3.6/base64.py", line 553, in decodebytes
return binascii.a2b_base64(s)
binascii.Error: Incorrect padding

I am using Magic Winmail Server2.4(build 0530) as a SMTP server, which appears 
dont support initial_response, so I set initial_response_ok=False and got this 
Error. 
currently I catch this error and ignore it to evade program failed, it works 
fine. Is there better way to fix this problem?

Thanks!

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components: email
messages: 392039
nosy: barry, junpengruan, r.david.murray
priority: normal
severity: normal
status: open
title: binascii.Error raised in smtplib when initial_response_ok=False
type: behavior
versions: Python 3.6, Python 3.7, Python 3.8, Python 3.9

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