Hi Tim, Thanks for this. The filename generation with temporary name in it looks good. As for the credit, I discovered this vulnerability and passed it on to VeriSign, so I'd appreciate it if you could add 1 more credit in the patch / bug announcement as:
Discovered by: Dawid Golunski (http://legalhackers.com) As for the CVEID, I think we should email this to [email protected] Thanks. On Wed, Aug 17, 2016 at 4:48 PM, Tim Rühsen <[email protected]> wrote: > Please review / test this patch. > > Please check the 'Reported-by' in the commit message and if you got a CVE > number, please report for inclusion into the commit message (and/or the code). > > Regards, Tim > > On Mittwoch, 17. August 2016 10:40:35 CEST Dawid Golunski 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 <[email protected]> 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
