Hi, In May 2017, user "Orange" found a vulnerability in the urllib fix for CVE-2016-5699 (HTTP Header Injection vulnerability): https://bugs.python.org/issue30458 It allows to inject arbitrary HTTP headers. Copy of their message: """ Hi, the patch in CVE-2016-5699 can be broke by an addition space. http://www.cvedetails.com/cve/CVE-2016-5699/ https://hg.python.org/cpython/rev/bf3e1c9b80e9 https://hg.python.org/cpython/rev/1c45047c5102 import urllib, urllib2 urllib.urlopen('http://127.0.0.1\r\n\x20hihi\r\n :11211') urllib2.urlopen('http://127.0.0.1\r\n\x20hihi\r\n :11211') """ Last month, the same bug has been rediscovered by user "ragdoll.guo": https://bugs.python.org/issue36276 Almost one year after the bug has been reported, no one came with a solution. I'm not comfortable with having known security issues impacting HTTP. Can someone please have a look at the issue and try to write a change to fix the issue? According to Karthikeyan Singaravelan, the Go language fixed a similar issue in Go 1.12: throw an error if the URL contains any control character. If we decide that the issue is not a security issue, we should document the behavior properly and close the issue. See also this related issue: "urlopen URL with unescaped space" https://bugs.python.org/issue14826 Victor -- Night gathers, and now my watch begins. It shall not end until my death.