Date: Mon, 10 Feb 2014 12:10:01 +0000 From: Simon McVittie <smcv@...ian.org> To: oss-security@...ts.openwall.com Subject: Re: Re: CVE request: python-gnupg before 0.3.5 shell injection On 09/02/14 21:40, cve-assign@...re.org wrote: > First, it seems that the shell_quote function in version 0.3.5 has > two fundamentally different problems with different flaw types and > different discoverers. I think the underlying problem here is that a library for interacting with GNUPG from Python is trying to implement Unix shell escaping. Unix shell escaping is subtle and easy to get wrong, so libraries whose intended scope does not include "miscellaneous OS/runtime utilities" should be delegating this to a better-tested and better-audited implementation. If possible, the preferred way to start a subprocess should be without going via /bin/sh: in Python, using functions from the subprocess module, without using the argument shell=True, achieves this. This is analogous to posix_spawn() (or fork()/exec()) in plain C, g_spawn_[a]sync() in GLib and so on. If python-gnupg really does need to go via a shell, analogous to system() in plain C or g_spawn_command_line_[a]sync() in GLib, then it should use a library function analogous to GLib's g_shell_quote(). Python's shlex.quote() seems ideal for this, but unfortunately it's new in version 3.3. Python 2.7 does document pipes.quote(), and the documentation indicates that pipes.quote() may have been present-but-undocumented in previous versions. As a worst case, as much as I hate to encourage embedded code copies, copying the implementation of shlex.quote() or pipes.quote() seems likely to yield better results than reimplementing it. S
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