couldn't you just use whatever secure mkstmp is appropriate for the language wget is written in http://rosettacode.org/wiki/Secure_temporary_file
so much easier and secure then faffing about. On Wed, Aug 17, 2016 at 7:40 AM, Dawid Golunski <da...@legalhackers.com> wrote: > Random file name + .part extension on temporary files would already be > good improvement (even if still stored within the same directory) and > help prevent the exploitation. > > Thanks. > > On Wed, Aug 17, 2016 at 9:22 AM, Tim Rühsen <tim.rueh...@gmx.de> wrote: > > On Mittwoch, 17. August 2016 13:37:33 CEST Ander Juaristi wrote: > >> I was thinking we could rename php extensions to phps, but it's all the > >> same thing in the end, and even better, since the former applies to any > >> kind of file and I've seen some broken servers that actually run phps > files. > >> > >> So, this is what I would do: > >> > >> 1. Write temporary files with 600 perms, and make sure they're owned > >> by the running user and group. qmail goes even further [1] by not > >> letting root run, but I would not do that here. > >> 2. Use mkostemp() to generate a unique filename and give it a > >> harmless extension (like Mozilla's .part). We already have unique_name() > >> in utils.c, altough it returns the file name untouched if it does not > >> exist. We should do some research on whether we could reuse parts of it. > > > > Giuseppe and I have a working patch that is basically like this. We are > still > > discussing the details (mkstemp extension, fixed extension, both or > maybe a > > mkdtemp directory where we put all the temp files). > > > > As soon as we agree, we'll post the patch here for further > discussion/review. > > > >> 3. Place them in /tmp, or even better, in ~/.wget-tempfiles, or > >> something like that. > > > > /tmp often is on a separate filesystem (e.g. RAM disk) with limited > space. > > This could open another (DOS) attack vector. > > > > You do not always have a home directory when running Wget. > > > >> There's a patch by Tim somewhere in this list that already does 1 (but > >> please, remove the braces ;D). > >> > >> It also comes to my mind, instead of writing each temp file to its own > >> file, we could put them all in the same file (with O_APPEND). But a) we > >> need a way to tell them apart later, and b) it may cause problems in > >> NFS, according to open(2). > >> > >> [1] http://cr.yp.to/qmail/guarantee.html > >> > >> On 15/08/16 18:31, Tim Rühsen wrote: > >> > On Montag, 15. August 2016 10:02:55 CEST moparisthebest wrote: > >> >> Hello, > >> >> > >> >> I find it extremely hard to call this a wget vulnerability when SO > many > >> >> other things are wrong with that 'vulnerable code' implementation it > >> >> isn't even funny: > >> >> > >> >> 1. The image_importer.php script takes a single argument, why would > it > >> >> download with the recursive switch turned on? Isn't that clearly a > bug > >> >> in the php script? Has a php script like this that downloads all > files > >> >> from a website of a particular extension ever been observed in the > wild? > >> >> > >> >> 2. A *well* configured server would have a whitelist of .php files it > >> >> will execute, making it immune to this. A *decently* configured > server > >> >> would always at a minimum make sure they don't execute code in > >> >> directories with user provided uploads in them. So it's > additionally a > >> >> bug in the server configuration. (incidentally every php package I've > >> >> downloaded has at minimum a .htaccess in upload directories to > prevent > >> >> this kind of thing with apache) > >> >> > >> >> It seems to me like there has always been plenty of ways to shoot > >> >> yourself in the foot with PHP, and this is just another iteration on > a > >> >> theme. > >> > > >> > Hi, > >> > > >> > this is absolutely true and your points were the first things that > came to > >> > my mind when reading the original post. > >> > > >> > But there is also non-obvious wget behavior in creating those (temp) > files > >> > in the filesystem. And there is also a long history of attack vectors > >> > introduced by temp files as well. > >> > > >> > Today the maintainers discussed a few possible fixes, all with pros > and > >> > cons. I would like to list them here, in case someone likes to > comment: > >> > > >> > 1. Rewrite code to keep temp files in memory. > >> > Too complex, needs a redesign of wget. And has been done for wget2... > >> > > >> > 2. Add a harmless extension to the file names. > >> > Possible name collision with wanted files. > >> > Possible name length issues, have to be worked around. > >> > > >> > 3. Using file mode 0 (no flags at all). > >> > Short vulnerability when changing modes to write/read the data. > >> > > >> > 4. Using O_TMPFILE for open(). > >> > Just for Linux, not for every filesystem available. > >> > > >> > 5. Using mkostemp(). > >> > Possible name collision with wanted files (which would be unexpectedly > >> > named as *.1 in case of a collision). At least the chance for a > collision > >> > seems very low. > >> > > >> > Any thoughts or other ideas ? > >> > > >> > Regards, Tim > > > > > > -- > Regards, > Dawid Golunski > http://legalhackers.com > -- -- Kurt Seifried -- Red Hat -- Product Security -- Cloud PGP A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993 Red Hat Product Security contact: secal...@redhat.com