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Title: [CVE-2019-9947] Header Injection in urllib
Type: security Stage: resolved
Components: Library (Lib) Versions: Python 3.8, Python 3.7, Python 3.6, Python 3.4, Python 3.5, Python 2.7
Status: closed Resolution: duplicate
Dependencies: Superseder: [security][CVE-2019-9740][CVE-2019-9947] HTTP Header Injection (follow-up of CVE-2016-5699)
View: 30458
Assigned To: Nosy List: christian.heimes, gregory.p.smith, martin.panter, matrixise, orsenthil, push0ebp, vstinner, ware
Priority: normal Keywords: patch, patch, patch

Created on 2019-02-06 00:32 by push0ebp, last changed 2022-04-11 14:59 by admin. This issue is now closed.

Pull Requests
URL Status Linked Edit
PR 11768 closed matrixise, 2019-02-06 08:30
PR 12524 closed push0ebp, 2019-03-24 14:24
Messages (7)
msg334896 - (view) Author: Sihoon Lee (push0ebp) * Date: 2019-02-06 00:32
this patch can also be broken by path and query string.

can succeed to inject HTTP header and be more critical by bypassing illegal header check

# Vulnerability PoC

>>> import urllib.request

>>> urllib.request.urlopen('\r\nHeader: Value\r\nHeader2: \r\n')
>>> urllib.request.urlopen('\r\nHeader: Value\r\nHeader2: \r\n')

> nc -lv 1234
GET /?q=HTTP/1.1
Header: Value
Header2: HTTP/1.1
Accept-Encoding: identity
User-Agent: Python-urllib/3.8
Connection: close

we can inject headers completely.

## Redis
redis also be affected by bypassing SSRF protection checking header "host:" with this injection.

>>> urllib2.urlopen('\r\nSET VULN POC\r\nHeader2:\r\n').read()
'$-1\r\n+OK\r\n-ERR unknown command `Header2:`, with args beginning with: `HTTP/1.1`, \r\n-ERR unknown command `Accept-Encoding:`, with args beginning with: `identity`, \r\n'

$ redis-cli> GET VULN

# Root Cause

- _hostprog = re.compile('^//([^/?]*)(.*)$')
+ _hostprog = re.compile('//([^/#?]*)(.*)', re.DOTALL)

It could succeed to parse host because of re.DOTALL
re.DOTALL gave the opportunity of injection.

this version of the commit was 3.4.7+

this vulnerability can be affected 3.4.7+ ~ 3.8-dev <- I tested it.
also, python 2.7.15 can be affected. I don't know which python2 version is affected because not test.

maybe after the commit, all of higher versions can trigger this vulnerability.

# Conclusion
this patch provides more critical vulnerability to bypass the illegal header check.
and we can inject HTTP header completely in urlopen() from this patch.

(Although this vulnerability is old on 12 Jul 2017, I don't know why no one has submitted issue still now XDD)
msg334906 - (view) Author: Stéphane Wirtel (matrixise) * (Python committer) Date: 2019-02-06 08:32
Hi all,

Not sure for the right way for this fix but here is a PR. I am interested by your feedback.

Thank you
msg334999 - (view) Author: Sihoon Lee (push0ebp) * Date: 2019-02-07 03:05
Sorry, I'm late.
My review is here.
msg335000 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2019-02-07 03:34
Maybe related to Victor's "Issue 1" described in Issue 32085. That is also a security bug about CRLF in the URL's path, but was opened before Issue 30500 was opened and the code changed, so I'm not sure if it is the same as this or not.

Also there is Issue 13359, a proposal to automatically percent-encode invalid URLs. For a security fix, I'm not sure but it might be safer to raise an exception, rather than rewriting the invalid URL to a valid one.
msg335005 - (view) Author: Sihoon Lee (push0ebp) * Date: 2019-02-07 06:20
Yes, I thought so. before the commit version i said, the previous version(~3.4.6), raised an exception(no host given~) in urlopen failing parsing host.
If this patch wants to be same as the previous version, It is right to raise an exception like the previous version.
I thought there is no exact answer, only depends on Python features.
msg339835 - (view) Author: STINNER Victor (vstinner) * (Python committer) Date: 2019-04-10 08:51
According to, the CVE-2019-9947 has been assigned to this issue.
msg339842 - (view) Author: Gregory P. Smith (gregory.p.smith) * (Python committer) Date: 2019-04-10 09:32
my fix proposed in issue30458 fixes this issue.

i do not think this one deserved its own CVE; at least's current text also points to the other one.
Date User Action Args
2022-04-11 14:59:10adminsetgithub: 80087
2019-04-10 09:32:49gregory.p.smithsetkeywords: patch, patch, patch
status: open -> closed
stage: patch review -> resolved
2019-04-10 09:32:36gregory.p.smithsetnosy: + gregory.p.smith
messages: + msg339842

superseder: [security][CVE-2019-9740][CVE-2019-9947] HTTP Header Injection (follow-up of CVE-2016-5699)
keywords: patch, patch, patch
resolution: duplicate
2019-04-10 08:51:12vstinnersettitle: Header Injection in urllib -> [CVE-2019-9947] Header Injection in urllib
nosy: + vstinner

messages: + msg339835

keywords: patch, patch, patch
2019-04-09 15:44:44waresetnosy: + ware
2019-03-24 14:31:57xtreaksetkeywords: patch, patch, patch
nosy: + orsenthil
2019-03-24 14:30:26push0ebpsetpull_requests: - pull_request12476
2019-03-24 14:25:01push0ebpsetpull_requests: + pull_request12476
2019-03-24 14:24:40push0ebpsetpull_requests: + pull_request12475
2019-03-24 14:18:17push0ebpsetpull_requests: - pull_request12474
2019-03-24 14:15:43push0ebpsetpull_requests: + pull_request12474
2019-02-07 06:20:03push0ebpsetmessages: + msg335005
2019-02-07 03:34:00martin.pantersetkeywords: patch, patch, patch

messages: + msg335000
2019-02-07 03:05:31push0ebpsetmessages: + msg334999
2019-02-06 08:56:06matrixisesetpull_requests: - pull_request11730
2019-02-06 08:55:55matrixisesetpull_requests: - pull_request11731
2019-02-06 08:32:11matrixisesetkeywords: patch, patch, patch
nosy: + matrixise
messages: + msg334906

2019-02-06 08:30:42matrixisesetkeywords: + patch
stage: patch review
pull_requests: + pull_request11731
2019-02-06 08:30:36matrixisesetkeywords: + patch
stage: (no value)
pull_requests: + pull_request11730
2019-02-06 08:30:28matrixisesetkeywords: + patch
stage: (no value)
pull_requests: + pull_request11729
2019-02-06 02:23:47xtreaksetnosy: + martin.panter
2019-02-06 00:33:33rhettingersetnosy: + christian.heimes
2019-02-06 00:32:11push0ebpcreate