Wrong attachement filename when mail mime header was too long

[manfred-kaiser]

BPO	39040
Nosy	@warsaw, @bitdancer, @maxking, @miss-islington, @manfred-kaiser
PRs	bpo-39040: added whitespaced to linesep_splitter in email.policy #17590 bpo-39040: Fix parsing of email mime headers with whitespace between encoded-words. #17620 [3.9] bpo-39040: Fix parsing of email mime headers with whitespace between encoded-words. (gh-17620) #20504 [3.8] bpo-39040: Fix parsing of email mime headers with whitespace between encoded-words. (gh-17620) #20505 [3.7] bpo-39040: Fix parsing of email mime headers with whitespace between encoded-words. (gh-17620) #20506
Files	testscript.py: Script to read filenames error.eml: Mail with broken filename original_mail_from_gmail.eml: downloaded mail from gmail (web interface). I only edited the the mail addresses for privacy reasons. Same problem with this mail

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-12-13.16:59:51.619>
labels = ['3.8', 'type-bug', '3.7', 'expert-email', '3.9']
title = 'Wrong attachement filename when mail mime header was too long'
updated_at = <Date 2020-05-29.11:43:51.599>
user = 'https://github.com/manfred-kaiser'

bugs.python.org fields:

activity = <Date 2020-05-29.11:43:51.599>
actor = 'miss-islington'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2019-12-13.16:59:51.619>
creator = 'mkaiser'
dependencies = []
files = ['48775', '48776', '48777']
hgrepos = []
issue_num = 39040
keywords = ['patch']
message_count = 23.0
messages = ['358343', '358345', '358350', '358351', '358352', '358378', '358384', '358393', '358395', '358396', '358458', '358460', '358463', '358500', '358530', '358573', '358608', '358853', '358857', '370276', '370298', '370299', '370300']
nosy_count = 5.0
nosy_names = ['barry', 'r.david.murray', 'maxking', 'miss-islington', 'mkaiser']
pr_nums = ['17590', '17620', '20504', '20505', '20506']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39040'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[manfred-kaiser]

I'm working on a mailfilter in python and used the method "get_filename" of the "EmailMessage" class.

In some cases a wrong filename was returned. The reason was, that the Content-Disposition Header had a line break and the following intention was interpreted as part of the filename.

After fixing this bug, I was able to get the right filename.

I had to change "linesep_splitter" in "email.policy" to match the intention.

Old Value:

linesep_splitter = re.compile(r'\n|\r')

New Value:

linesep_splitter = re.compile(r'\n\s+|\r\s+')

[bitdancer]

Thanks for the report. Can you provide an example that reproduces the problem?

Per the RFC, lines may be broken before whitespace in certain places in certain headers, but that does not make the whitespace go away. Only the crlf sequence is removed when unfolding the header, per the RFC, so your proposed fix is incorrect. I suspect your example header is invalid, and the question will then become is there some sort of Postel-style error recovery we can and want to do in the function that parses the content-disposition header.

[manfred-kaiser]

The original filename is "Schulbesuchsbestättigung.pdf", but when I use the method "get_filename" I got "Schulbesuchsbestättigung. pdf"

I removed some headers from the mail for privacy reasons