Eliminating this makes sense to me given the security benefit. Thank you for pushing it! But it does seem somewhat risky from a web compat perspective. 0.005% is above our "small but non-trivial risk <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.mqfkui78vo5z>" rule of thumb. Here's a bit of an analysis according to our other compat principles <http://bit.ly/blink-compat>:
- Severity of breakage <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.u5ya6jvru7dl>: lower given this is likely only about some visualis, but this site <https://jobs.nzz.ch/> is a good example of non-trivial UI breakage. This pattern of putting a base64-encoded SVG into an SVG <use> element with nothing else in the <svg> is weird, isn't it? Why would someone do that rather than just put the SVG in directly, or put the data URL into an img tag? I don't suppose there's some creative way to allow this specific odd pattern while still getting the security benefit, is there? - Unique sites impacted <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.4k9u8ddizqrq>: Finding a variety of small sites is actually a lot worse than if we had found only a few bigger sites. It means there's probably some common tool or pattern leading different designers/developers to do this and so likely a relatively large number of individuals who would need to be involved in fixing the breakage. Of course our HTTP Archive list of sites is just a subset of who's fully impacted, so if the problem is a long-tail one as it seems, HTTP archive data shows us only the tip of that long tail. - Security <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.iklh96dxj81w>: it's definitely worth taking some comapt risk to reduce XSS surface area. I don't fully understand the threat model though. Is this mainly a risk for sites who are programmatically putting (potentially attacker-controlled) strings into SVGUseElement hrefs? Or are you more worried about cases where the attacker controls the HTML and can take advantage of this oddity in the platform on any normal site? I'm just trying to gauge the magnitude of the security benefit here to weigh it against the comapt risk, any help is appreciated. - Ease of adaptation <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.x5bhg5grhfeo>: seems like it should be easy to use an alternative, at least for these image cases, but I guess it's hard to say without knowing why people are doing this. Is there perhaps some website design tool which is generating this and will need to change? - Interop <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.4hjbxw7513sw>: The fact that this doesn't work in Safari is a vote in favor of breaking it in chromium to achieve interop. It does work in Firefox though. - Standards conformance <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.xcsa26ortrmi>: This is allowed by spec today, so breaking it requires some more diligence - Enterprise <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.axcg738lzcs9>: Being broken in Safari is an indication the risk will be higher in enterprise software which is often chromium-only. We may need to go through the enterprise breaking change process <https://www.chromium.org/developers/enterprise-changes/>. - Outreach <https://docs.google.com/document/d/1RC-pBBvsazYfCNNUSkPqAVpSpNJ96U8trhNkfV0v9fk/edit#heading=h.t9ade4ywppcg>: Given the relatively high usage, if we want to proceed with this plan I think this is the main opportunity for mitigations. Can we try contacting some of these sites we've identified to understand why they're using this pattern? Is there a tool generating this pattern which we can get updated before we make the change? I think we'd need a blog post capturing what we've learned from talking with a few customers who have done this and how they fixed it for their UI design flow. Sorry it's not looking to be an easy decision, but I hope this gives you some ideas for how we might be able to reduce the risk to a point that we could proceed. WDYT? Rick On Thu, Jan 12, 2023 at 3:11 PM 'Jun Kokatsu' via blink-dev < blink-dev@chromium.org> wrote: > On Thu, Jan 12, 2023 at 10:44 AM Mike Taylor <miketa...@chromium.org> > wrote: > >> On 1/11/23 6:49 PM, 'Jun Kokatsu' via blink-dev wrote: >> >> Contact emails >> >> jkoka...@google.com >> >> Specification >> >> https://svgwg.org/svg2-draft/struct.html#UseElementHrefAttribute >> >> https://github.com/w3c/svgwg/pull/901/files >> >> Summary >> >> Assigning a data: URL in SVGUseElement can cause XSS. And this also led >> to a Trusted Types bypass. >> >> Therefore, we plan to deprecate and remove support for it. >> >> >> Blink component >> >> Blink>SVG >> <https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3ESVG> >> >> Motivation >> >> Assigning an attacker controlled string to SVGUseElement.href causes XSS >> and a Trusted Types bypass >> <https://github.com/w3c/trusted-types/issues/357> because of data: URLs. >> If we fix this bug by requiring TrustedScriptURL assignment to >> SVGUseElement.href under Trusted Types enforcement, many sites would need >> to refactor code (even for same-origin URL or Blob URL assignment). >> >> Since Webkit does not support data: URLs in SVGUseElement and both >> Mozilla and Webkit are supportive for the removal, we think that removing >> support for data: URLs in SVGUseElement is the right way to solve this >> problem. >> >> Additionally, data: URLs can only trigger script execution in script >> loaders such as HTMLScriptElement.src or dynamic import >> <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import>. >> However, SVGUseElement is an exception to this, which also caused a >> bypass >> <https://bugs.chromium.org/p/chromium/issues/detail?id=1306450#c10> in >> the Sanitizer API. We believe that this also led to several other bugs in >> sanitizers and linters missing a check for this special case. >> >> The usage >> <https://chromestatus.com/metrics/feature/timeline/popularity/4356> of >> data: URLs in SVGUseElement is about 0.005%. >> >> Digging into the HTTP Archive shows usages in ~50 sites. There are 2 >> major sites (slickdeals.net and hunter.104.com.tw) which use data: URLs >> in SVGUseElement. >> >> The use in slickdeals.net is invisible (i.e. used in the footer but >> doesn't appear), and hunter.104.com.tw is using it for a single icon in >> the footer (which is already broken when rendered in Webkit). Rest of the >> usages seems to be in individual small sites. >> >> I poked around the 10 sample sites at the bottom of the use counter: >> >> https://www.aspareanord.it/, https://www.umbria.camcom.it, >> https://www.bisenzio.it/, https://www.comune.vernio.po.it/, >> https://appaltinnovativi.gov.it/, https://www.gdf.gov.it/, >> https://www.us.schott.com/, https://shop.wavin.com/, https://jobs.nzz.ch/, >> https://www.learnapp.com/ >> >> For the 6 Italian sites (I guess the same agency made them?), the right >> arrow icon next to "Vedi" would disappear. For a site like >> https://jobs.nzz.ch - there's a number of visually significant design >> icons that would be gone towards the bottom (and yes, it looks sort of >> broken today in Safari). >> >> It's not the end of the world, looking at these 10 sites, but I wonder >> how a developer would know how to fix this. Have you considered a DevTools >> issue? >> > > Thank you for the suggestion! Yes, I do plan to follow Deprecation steps > <https://chromium.googlesource.com/chromium/src/+/HEAD/third_party/blink/renderer/core/frame/deprecation/README.md> > and > add a Devtools issue 🙂 > >> Initial public proposal >> >> TAG review >> >> TAG review status >> >> Not applicable. >> >> Because this intent removes part of a feature, and it is already shipped >> in Webkit (i.e. never supported). >> >> Risks >> >> Interoperability and Compatibility >> >> Gecko: Positive >> <https://github.com/mozilla/standards-positions/issues/718> >> >> WebKit: Positive >> <https://github.com/WebKit/standards-positions/issues/108> >> >> Web developers: No signals >> >> >> Debuggability >> >> Is this feature fully tested by web-platform-tests >> <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md> >> ? >> >> Yes <https://github.com/web-platform-tests/wpt/pull/37511> >> >> Flag name >> >> RemoveDataUrlInSvgUse >> >> >> Requires code in //chrome? >> >> False >> >> Tracking bug >> >> https://bugs.chromium.org/p/chromium/issues/detail?id=1300195 >> >> Estimated milestones >> >> Deprecate for 2 milestones, then remove depending on breakages. >> >> Can you say more about what the deprecation looks like (i.e., blog post, >> deprecation reports, devtools issue, etc)? >> >> >> >> Link to entry on the Chrome Platform Status >> >> https://chromestatus.com/feature/5128825141198848 >> >> This intent message was generated by Chrome Platform Status >> <https://chromestatus.com/>. >> -- >> You received this message because you are subscribed to the Google Groups >> "blink-dev" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to blink-dev+unsubscr...@chromium.org. >> To view this discussion on the web visit >> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOWKMF6VXw7jmQoZM47i3ybzn%3D5Pc4mw26Khv9U9aP_UzBt-dg%40mail.gmail.com >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOWKMF6VXw7jmQoZM47i3ybzn%3D5Pc4mw26Khv9U9aP_UzBt-dg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> >> -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to blink-dev+unsubscr...@chromium.org. > To view this discussion on the web visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOWKMF5KQOG5R8baUM41T4fR01QbGFjvvEsf629h%2BzASCn_F0Q%40mail.gmail.com > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOWKMF5KQOG5R8baUM41T4fR01QbGFjvvEsf629h%2BzASCn_F0Q%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFUtAY9yaBNvQLwno9vOc2OFbmKZ6YRtrLOMtQYF2HLFbG5_xw%40mail.gmail.com.
