[whatwg] Priority between <a download> and content-disposition

Boris Zbarsky bzbarsky at MIT.EDU
Wed May 8 09:01:13 PDT 2013

On 5/8/13 10:45 AM, Gordon P. Hemsley wrote:
> I still think @download takes priority.
> The Content-Disposition header says, "Nevermind what filename the URL
> shows; this is really file B.txt."
> The @download attribute says, "Nevermind what filename this link would
> normally be; let's just consider it A.txt."

OK, that's at least a reasonable argument for the behavior.  ;)

> OK, technically, the way I phrased it, yes. But what I meant was that
> it rolls a bunch of steps into one, telling the browser that the link
> should be downloaded and named per suggestion.

Yes, but the key is _who_ is making the suggestion and why.

> That seems like quite a sophisticated attack that relies on a lot of
> things falling into place all at once.

Uh... yes.  Like most browser exploits.

> Then I think it is the responsibility of the UA to sniff the file and
> protect the user from such attempts to mislead.

This is not trivial, since sniffing can easily fail on files that are 
both HTML and png or both HTML and exe at the same time.  There's a good 
bit of research on things like this.

> There is a price to freedom, as they say. We shouldn't let a few
> rotten apples spoil the whole bunch.

If it's going to open users to exploits.... we do it all the time.

> I'm not sure I have the resources to do extensive real-world testing
> of this (and that documentation suggests it has been superseded in
> more modern OSes), but I don't think it would be unreasonable for the
> UA to override or augment the filename suggested by the @download
> attribute it if determines that it would not be in the best interest
> of the user to use the suggested filename unchanged.

Phrased that way, using the Content-Disposition filename is a perfectly 
valid "override if not in the best interest of the user" behavior, fwiw.


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