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Title: CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly parsed
Type: behavior Stage: resolved
Components: Library (Lib) Versions: Python 3.10, Python 3.9
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: orsenthil Nosy List: catalin.iacob, demian.brecht, martin.panter, miss-islington, mwatkins, orsenthil, petri.lehtinen, terry.reedy
Priority: normal Keywords: patch

Created on 2009-01-25 15:30 by mwatkins, last changed 2022-04-11 14:56 by admin. This issue is now closed.

File name Uploaded Description Edit
cgi-accept.patch martin.panter, 2015-02-15 04:26 review
Pull Requests
URL Status Linked Edit
PR 23638 merged orsenthil, 2020-12-04 11:57
PR 23657 merged miss-islington, 2020-12-05 14:57
Messages (6)
msg80510 - (view) Author: Mike Watkins (mwatkins) Date: 2009-01-25 15:30
There appears to have been a bug in how HTTP_ACCEPT is parsed living in 
run_cgi() for eons, perhaps from the time it was written. Perhaps not 
many are using this code (I'm not either) but recent (post 3.0 Release) 
Python 3.x appear to have broken something in getallmatchingheaders() 
(which originates in Message) and I happened to stumble upon this 
condition while searching through the stdlib code.

From Line 980 of http.server

        accept = []
        for line in self.headers.getallmatchingheaders('accept'):
            if line[:1] in "\t\n\r ":
                accept = accept + line[7:].split(',')
        env['HTTP_ACCEPT'] = ','.join(accept)

line[:1] in '\t\n\r' clearly was meant to to be line[-1].

However that doesn't fix completely this chunk of code as it makes some 
assumptions about what getallmatchingheaders() delivers which aren't 
accurate. The following behaves as expected and feels safer:

        accept = []
        for line in self.headers.getallmatchingheaders('accept'):
            if line.lower().startswith("accept:"):
                line = line[7:]
            for part in line.split(','):
                part = part.strip()
                if part:
        env['HTTP_ACCEPT'] = ','.join(accept)

Note that post Python 3.0 release, 
http.client.HTTPMessage.getallmatchingheaders() was broken. I've 
reported this just now and proposed a fix in #5053.
msg108657 - (view) Author: Terry J. Reedy (terry.reedy) * (Python committer) Date: 2010-06-26 00:10
I hope that someone who knows more than me on this subject takes a look at this.
msg236019 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2015-02-15 04:26
Posting a patch for this so that we can get rid of the broken HTTPMessage.getallmatchingheaders() method in Issue 5053.
msg236020 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2015-02-15 04:34
BTW in the original code, I think line[:1] in "\t\n\r " might have been correct. It looks like the getallmatchinheaders() method was actually meant to return continued lines separately, prefixed with whitespace. My patch is probably only appropriate for Python 3; maybe Mike’s code will work for Python 2.
msg382569 - (view) Author: miss-islington (miss-islington) Date: 2020-12-05 15:26
New changeset b630ca7bc13ba9bdf95cd7dce0ac8e1578fb53a0 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-5054: CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly parsed (GH-23638) (GH-23657)
msg382570 - (view) Author: Senthil Kumaran (orsenthil) * (Python committer) Date: 2020-12-05 16:00
This was also resolved in 3.10
Date User Action Args
2022-04-11 14:56:44adminsetgithub: 49304
2020-12-05 16:00:36orsenthilsetmessages: + msg382570
2020-12-05 15:59:51orsenthilsetstatus: open -> closed
resolution: fixed
stage: patch review -> resolved
2020-12-05 15:26:44miss-islingtonsetmessages: + msg382569
2020-12-05 14:57:01miss-islingtonsetnosy: + miss-islington
pull_requests: + pull_request22525
2020-12-04 11:57:22orsenthilsetpull_requests: + pull_request22506
2020-12-01 22:41:03orsenthilsetassignee: orsenthil
versions: + Python 3.9, Python 3.10, - Python 2.6, Python 3.1, Python 2.7, Python 3.2
2015-05-31 11:13:17martin.panterlinkissue5053 dependencies
2015-05-31 11:10:59martin.pantersetstage: patch review
2015-02-16 19:01:36demian.brechtsetnosy: + demian.brecht
2015-02-15 04:34:53martin.pantersetmessages: + msg236020
2015-02-15 04:26:24martin.pantersetfiles: + cgi-accept.patch

nosy: + martin.panter
messages: + msg236019

keywords: + patch
2012-11-26 08:25:36catalin.iacobsetnosy: + catalin.iacob
2011-11-23 19:26:41petri.lehtinensetnosy: + petri.lehtinen
2010-06-26 02:21:49r.david.murraysetnosy: + orsenthil
2010-06-26 00:10:37terry.reedysetnosy: + terry.reedy

messages: + msg108657
versions: + Python 3.2, - Python 2.5, Python 2.4, Python 3.0
2009-01-25 15:30:02mwatkinscreate