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Re: [xsl] HTML5 semantics and XSLT
2022-02-23 12:30:48
Hi,
Mike Kay is right, this has nothing to do with the MathML namespace. Any
namespace would do. (The MathML namespace just happened to turn up in the place
where this purported exploit was described.) David and Norm are also right that
this is not an XSLT bug or an XML bug: they are working as designed.
Others are saying they can't even see the offending < s c r i p t xmlns =
whathaveyou>(script)< / s c r I p t > that I typed into my email, which
suggests scrubbing - not entirely surprising I suppose! It's a good thing the
list doesn't take attachments, I guess, or my alert("Boo") might be fired off
somewhere.
Cheers, Wendell
From: Michael Kay mike(_at_)saxonica(_dot_)com
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>
Sent: Wednesday, February 23, 2022 11:48 AM
To: xsl-list <xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com>
Subject: Re: [xsl] HTML5 semantics and XSLT
I don't think I've understood the significance of the mathml namespace in all
this.
And presumably any harm that can be done using this exploit could equally be
done by executing untrusted HTML in the browser directly?
Michael Kay
Saxonica
On 23 Feb 2022, at 16:31, Piez, Wendell A. (Fed)
wendell(_dot_)piez(_at_)nist(_dot_)gov<mailto:wendell(_dot_)piez(_at_)nist(_dot_)gov>
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>>
wrote:
Friends,
Starting from an interesting post at
https://blog.sonarsource.com/horde-webmail-account-takeover-via-email<https://gcc02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fblog.sonarsource.com%2Fhorde-webmail-account-takeover-via-email&data=04%7C01%7Cwendell.piez%40nist.gov%7C4fb0caa1e98d4d84cb5808d9f6ec3b37%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C637812316750696466%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=GCSrguxHP%2BqKgmR0elMen1jVYniB0v9Fn3RVJAI8F7s%3D&reserved=0>
(brought to my attention by a colleague) ...
Amazingly, it appears to be true that opened in a current web browser, a
document like the following will proceed to execute the script it contains.
<!DOCTYPE html>
<html
xmlns="http://www.w3.org/1999/xhtml<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.w3.org%2F1999%2Fxhtml&data=04%7C01%7Cwendell.piez%40nist.gov%7C4fb0caa1e98d4d84cb5808d9f6ec3b37%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C637812316750696466%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=AHMNKUdTdDXU5bc2NBTTKZpCtNFCS2TENDmxm0CmLos%3D&reserved=0>">
<head>
<title>Boo?</title>
</head>
<body>
</body>
</html>
NB: yes, that supposed MathML is bogus. FWIW this is also different from the
code snippet in the post, which isn't actually realistic. But it documents a
real phenomenon.
The reason I remark on this is that (as noted in the post) it implies that any
template such as this (copied from a widely distributed library), when
targeting HTML, might be problematic on some uncontrolled inputs:
<xsl:template match="*" mode="math">
<xsl:element name="{local-name()}"
namespace=http://www.w3.org/1998/Math/MathML<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML&data=04%7C01%7Cwendell.piez%40nist.gov%7C4fb0caa1e98d4d84cb5808d9f6ec3b37%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C637812316750696466%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=67vjn50nTWtT97eyUzIvzhoXtPuJfeenRxOh8qNnyIc%3D&reserved=0>>
<xsl:apply-templates select="@*|node()" mode="math"/>
</xsl:element>
</xsl:template>
Might this need to be defended, maybe by emitting a prefix on every element
name it makes?
<xsl:template match="*" mode="math">
<xsl:element name="mml:{local-name()}"
namespace=http://www.w3.org/1998/Math/MathML<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML&data=04%7C01%7Cwendell.piez%40nist.gov%7C4fb0caa1e98d4d84cb5808d9f6ec3b37%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C637812316750696466%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=67vjn50nTWtT97eyUzIvzhoXtPuJfeenRxOh8qNnyIc%3D&reserved=0>>
<xsl:apply-templates select="@*|node()" mode="math"/>
</xsl:element>
</xsl:template>
Otherwise, at least as reported in the post cited above, an OpenOffice
document, when previewed in certain execution contexts, can act much like a
Word document with embedded malware.
Comments?
Regards, Wendell
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