- From: Chris Palmer <palmer@google.com>
- Date: Mon, 8 Feb 2016 10:27:36 -0800
- To: Craig Francis <craig.francis@gmail.com>
- Cc: Frederik Braun <fbraun@mozilla.com>, public-webappsec@w3.org
- Message-ID: <CAOuvq22R6BGEKNgXBeV6oL=Ry8BXkdWQBKx6Js-1CFRNeLGiHQ@mail.gmail.com>
I also prefer The Simplest Thing That Could Possibly Work. To me that would seem to be the string in/string out interface, or a string in/tree of DOM Nodes interface (then the caller could do something like: e.appendChild(purify(bad_string)) ). Or both. On Feb 8, 2016 1:37 AM, "Craig Francis" <craig.francis@gmail.com> wrote: > As a web developer who frequently has to sanitise HTML (more so server > side), I would still like to see this. > > But creating a safe node list will be difficult. > > Take the <a> as an example, imagine a forum with a WYSIWYG (/me > shudders)... some forums won't like this at all (SEO spamming), some may > consider this safe if it has a rel=nofollow... but many will forget the > href="javascript:...", which is a valid attribute on a valid node, but > getting a click event can cause inline JavaScript to run (assuming no CSP > that blocks unsafe-inline). > > If you know how to solve this (both as a Sanitiser or under a Safe Node), > then I'll be very happy. > > Craig > > > > > On 8 Feb 2016, at 08:48, Frederik Braun <fbraun@mozilla.com> wrote: > > > > Hi, > > > > I think there is a need for a client-side HTML/XSS sanitization > > mechanism that lives in the browser (i.e., where the parser is). > > AFAIU, previous discussion has shown that there are no strong objections > > to this, but feel free to look the previous thread [1] or Mario > > Heiderich's presentation from Usenix Enigma [2] for further reading. > > > > I think that a first version of this spec should be a JavaScript API > > that consumes a string of potentially dangerous markup and returns a > > string that is clean. > > > > A Safe Node is certainly more interesting, but I'm afraid that we (the > > working group) are sometimes too detached from the needs of a modern web > > application and that we should start with providing something useful > *soon*. > > As we have seen with CSP, it's always harder to retrofit a new security > > system to an existing architecture. But the "String In - String Out" > > approach will certainly fit into every app. We can still do the Safe > > Node in a follow-up, if the initial feedback is good. > > > > Another outcome of the reduced first version would be a public, vetted > > and testable whitelist of safe DOM Nodes. This is useful for all > > existing custom sanitizers and is a positive outcome of its own [3]. > > > > I expect that this first version will be easy to implement, given that > > existing browsers use already this internally, albeit not exposed to web > > content. > > > > In the long run, attackers might race towards finding and abusing parser > > bugs and more quirks like those which Mario has called mXSS (mutation > > XSS) [4]. This is good, as it will guide us to what a Safe Node will > > need and prove that we have indeed risen the bar beyond trivial XSS > > exploits. > > > > Thoughts? > > > > > > Cheers, > > Frederik > > > > > > [1] For the initial thread "In-browser sanitization vs. a “Safe Node” in > > the DOM" see > > > https://lists.w3.org/Archives/Public/public-webappsec/2016Jan/thread.html > > > > [2] Link to his slides and the abstract at > > > https://www.usenix.org/conference/enigma2016/conference-program/presentation/heiderich > > > > [3] Obsolete whitelist at WHATWG wiki: > > https://wiki.whatwg.org/wiki/Sanitization_rules > > > > [4] "mXSS Attacks: Attacking well-secured Web-Applications > > by using innerHTML Mutations", see https://cure53.de/fp170.pdf > > > >
Received on Monday, 8 February 2016 18:28:05 UTC