Gregory's ServerI'm wondering if I can give untrusted authors the ability to go wild with custom SVG in a framed-off fixed size area of a web page, without breaching the security of the wider page or application
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18 comments
 This is great! This Cloudflare Rust library includes a detailed test suite that tells me everything I wanted to know https://mastodon.theorangeone.net/@jake/113370469717181352 Even better... it looks like I can point to them from a regular img tag and the SVG spec has me covered: https://www.w3.org/TR/SVG2/conform.html#secure-static-mode ... and it looks like that means I can do an img tag with an src that points to a base64 encoded SVG object and any nasty JavaScript etc will be disabled for me - here's an example which seems to demonstrate that working https://gistpreview.github.io/?03f0076446027b9b12e1ea14315db52b  @simon right, an img tag sandboxes them. What I do for svgshare.com is both display them as img and also run the svg through python html5lib and remove any script elements. (I also inline it in the upload dialogue so anyone trying to xss me does it to themselves instead). The other approach is what feedparser does and whitelist svg and html elements. @simon you can try stuff like https://github.com/cure53/DOMPurify. I am not sure that is the best one, but they exist (I wrote one, once upon a time).  @polotek yeah probably! I'm still trying to work up my confidence in those, detailed and comprehensive documentation on exactly what the sandbox attribute does has been hard to come by  @simon the JS in an SVG cannot interact with anything outside of itself. @simon <iframe sandbox> is useful here. You can even allow JavaScript but have it run in an opaque origin. @jaffathecake I'm desperately keen on learning the true ins and outs of that, but I've found detailed documentation (including browser support) on all of the options you can stuff in that sandbox attribute frustratingly difficult to locate @simon the table at the bottom of https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe is decent @jaffathecake it's the best I've seen but it still leaves me with so many questions... how good is browser support for each of those allowX things? What do browser security experts advise in terms of using them? I'm really paranoid :/ @simon the browser support for the various allow features is in the table at the end of the page  @simon @jaffathecake if you just want the SVG displayed, put them in an <img> tag. Otherwise, your favorite sanitizer library DOMPurify has great SVG support. (Iframe sandbox works really great too!!) |
@simon SVG can do a lot, but perhaps a Web Component that would only hold a single svg would sequester such an SVG and prevent it from attempting to suck in information about the enclosing page.