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Widened svg content attribute xss filtering

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Takes care of additional cases that can occur.
Closes #3705
This commit is contained in:
Dan Brown 2022-09-06 17:01:56 +01:00
parent 24f82749ff
commit 6955b2fd5a
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GPG Key ID: 46D9F943C24A2EF9
2 changed files with 7 additions and 3 deletions
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7
app/Util/HtmlContentFilter.php
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@ -45,10 +45,11 @@ class HtmlContentFilter
$badIframes = $xPath->query('//*[' . static::xpathContains('@src', 'data:') . '] | //*[' . static::xpathContains('@src', 'javascript:') . '] | //*[@srcdoc]');
static::removeNodes($badIframes);
// Remove tags hiding JavaScript or data uris in values attribute.
// Remove attributes, within svg children, hiding JavaScript or data uris.
// A bunch of svg element and attribute combinations expose xss possibilities.
// For example, SVG animate tag can exploit javascript in values.
$badValuesTags = $xPath->query('//*[' . static::xpathContains('@values', 'data:') . '] | //*[' . static::xpathContains('@values', 'javascript:') . ']');
static::removeNodes($badValuesTags);
$badValuesAttrs = $xPath->query('//svg//@*[' . static::xpathContains('.', 'data:') . '] | //svg//@*[' . static::xpathContains('.', 'javascript:') . ']');
static::removeAttributes($badValuesAttrs);
// Remove elements with a xlink:href attribute
// Used in SVG but deprecated anyway, so we'll be a bit more heavy-handed here.

3
tests/Entity/PageContentTest.php
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@ -333,6 +333,9 @@ class PageContentTest extends TestCase
'<svg><animate href=#xss attributeName=href values=javascript:alert(1) /></svg>',
'<svg><animate href="#xss" attributeName="href" values="a;javascript:alert(1)" /></svg>',
'<svg><animate href="#xss" attributeName="href" values="a;data:alert(1)" /></svg>',
'<svg><animate href=#xss attributeName=href from=javascript:alert(1) to=1 /><a id=xss><text x=20 y=20>XSS</text></a>',
'<svg><set href=#xss attributeName=href from=? to=javascript:alert(1) /><a id=xss><text x=20 y=20>XSS</text></a>',
'<svg><g><g><g><animate href=#xss attributeName=href values=javascript:alert(1) /></g></g></g></svg>',
];
$this->asEditor();