I responded to your mail that says "The problem described in the article was less about arbitrary people but someone who hacked through other security issues to become administrator with temple editing rights". So I thought that the premise there was that people who shouldn't be able to edit templates become able to do so. But it doesn't mater how it was in that case. Because as I said in the linked bug report, and as the FAQ says, if you allow someone to edit templates with the default FreeMarker configuration, that's almost like if you allow them to edit Java files. So whatever your application has right to do (like read the password file, launch missiles, etc.), the templates probably can do as well. The point of discouraging complex/technical logic in templates (not just in FreeMarker) was the MVC principle, where you should only put presentation logic into the templates.
We can't provide a practically useful default configuration that's secure if you can't trust people that can edit templates, because the whitelist content is specific to the concrete application. By default ?new is not restricted (well, it can instantiate TemplatModel-s only, but that hardly saves anyone security wise). The reason ?api is still disabled by default is that if someone went through the pain of setting up FreeMarker to be safe(r) (which implies that you do not use the default ObjectWrapper, nor the default settings for ?new, and you are thoughtful with your TemplateLoader, as the FAQ says), then the new FreeMarker version where ?api was introduced should not open a new hole on your system. For almost all users though, ?api enabled by default would be better (it's mostly to allow users to work around TemplateHashModel limitations when dealing with java.util.Map-s), but I have chosen the safer approach when I added it. The unsafeMethods mechanism will be updated, as things stand, despite that it's not strictly backward compatible. It will be still a quite pointless mechanism. I don't know why was it added by the author (some 10-15 years ago, I think). On Tue, Dec 24, 2019 at 4:14 PM Siegfried Goeschl < [email protected]> wrote: > Hi Daniel, > > Not sure about your line of thoughts :-) > > My understanding > > * There is a recipe out there how someone can access the file system and > the setup was not bad security-wise - only "?api" built-in was enabled > * I think the "?api.class.getResource" and > "?api.class.getResourceAsStream" can be marked as unsafe method? > * I also think that ALLOWS_NOTHING_RESOLVER is not the default > configuration? > * I actually tried the published code and it reads my "/etc/passwd" :( > > If the assumptions above are correct - can this particular attack be > avoided? If so we should react and improve the configuration ... > > Thanks in advance, > > Siegfried Goeschl > > > > On 24.12.2019, at 11:50, Daniel Dekany <[email protected]> wrote: > > > > The blog entry might starts its case with a privilege escalation > > independent of FreeMarker, but the question you got during your > > presentation wasn't about that, I think. But more importantly, some real > > world applications do allow editing templates for users who aren't > > necessarily some kind of superusers. Right now, after they realized that > > the problem exists at all, they will have to figure out a solution > > themselves. We are in a much better position to do the same. > > > > DOS-ing is certainly less of a concern in general, though unintentional > > DOS-ing (or I guess unintentional) was a problem for > > try.freemarker.apache.org in the past. My point there is just that if > > really everyone from the Internet can edit templates, then it will be a > > problem, I guess for any practical template language. > > > > > > On Mon, Dec 23, 2019 at 11:55 PM Siegfried Goeschl < > > [email protected]> wrote: > > > >> Hi Daniel, > >> > >> I guess I need to re-read the FreeMarker documentation and ticket - > having > >> said that > >> > >> * The problem described in the article was less about arbitrary people > but > >> someone who hacked through other security issues to become administrator > >> with temple editing rights > >> * The people having that skills usually don't have any interest in > >> starting a DOS attack by messing up templates - there are more valuable > >> things out there ... > >> * I think it is pretty much impossible to make FreeMarker 100% bullet > >> proof (tons of features, a lot of code, arbitrary libraries coming from > the > >> application) but at least we can check that this attack does not work > any > >> longer > >> * From my understanding - usually there a couple of security > >> vulnerabilites leading to complete data breach :-) > >> > >> Thanks in advance, > >> > >> Siegfried Goeschl > >> > >> > >>> On 23.12.2019, at 22:30, Daniel Dekany <[email protected]> > wrote: > >>> > >>> Hi, > >>> > >>> In short, allowing untrusted users to edit templates is not supported. > >> But, > >>> since people do it anyway, 2.3.30 will make an effort to allow doing > that > >>> with taking far less risk than what people take now. The > >> MemberAccessPolicy > >>> feature committed in recent days is the start of that. Actually, you > >> could > >>> always just use SimpleObjectWrapper (as the FAQ states), but clearly > >> that's > >>> too limiting for what many (most?) people use FreeMarker for. But > >> anyway, I > >>> don't believe that a template engine with the complexity of FreeMarker > >> will > >>> be ever a good fit for applications where random people can edit > >> templates. > >>> If users are accountable in real life for what they did, like they are > >>> employees at the client, then probably it will be good enough, but not > >> for > >>> use cases where anyone can edit templates. If nothing else, you will be > >> too > >>> easily DOS-able then. > >>> > >>> As of the blog entry, see this: > >>> https://issues.apache.org/jira/browse/FREEMARKER-124 > >>> Here I would add that it's likely that the calls used in the blog entry > >>> won't work anymore in 2.3.30. I'm a bit uneasy about that, as it's a > >>> backward compatibility risk (it won't be just blocking that single > >> method), > >>> while it doesn't provide real security. You need a whitelist of what's > >>> allowed for that (as opposed to a blacklist), and that's possible to do > >>> with MemberAccessPolicy, but I will also provide an implementation to > >> help > >>> doing that. > >>> > >>> Also, in the FAQ: > >>> > >> > https://freemarker.apache.org/docs/app_faq.html#faq_template_uploading_security > >>> > >>> > >>> On Mon, Dec 23, 2019 at 7:25 PM Siegfried Goeschl < > >>> [email protected]> wrote: > >>> > >>>> Hi folks, > >>>> > >>>> During my last presentation I was asked about how secure Apache > >> Freemarker > >>>> is in the context of user editing their templates - well, hard to say > >>>> without knowing the application. > >>>> > >>>> But I came across an interesting article (see > >>>> https://ackcent.com/blog/in-depth-freemarker-template-injection/) > where > >>>> the authors successfully hacked a CMS based on Apache FreeMarker > >>>> > >>>> * As far as I know the UNRESTRICTED_RESOLVER is the default? Maybe > >>>> ALLOWS_NOTHING_RESOLVER would be a better default? > >>>> * Enabling "?api" needs to be enabled by developers which is fine > >>>> * Update the "unsafeMethods.properties" according to the article? For > >> the > >>>> records "java.lang.Thread.suspend()" is duplicated anyway > >>>> > >>>> Thanks in advance, > >>>> > >>>> Siegfried Goeschl > >>>> > >>>> > >>> > >>> -- > >>> Best regards, > >>> Daniel Dekany > >> > >> > > > > -- > > Best regards, > > Daniel Dekany > > -- Best regards, Daniel Dekany
