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Drop unsafe SMIL attributeName values in SVG sanitization #911

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Drop unsafe SMIL attributeName values in SVG sanitization #911

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f686c4b
Add the possibility to specify attribute sanitization logic
giuscris Jun 27, 2026
179c3ac
Drop unsafe SMIL `attributeName` values in SVG sanitization
giuscris Jun 27, 2026
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32 changes: 20 additions & 12 deletions formwork/src/Sanitizer/DomSanitizer.php
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Original file line number Diff line number Diff line change
Expand Up @@ -231,22 +231,30 @@ protected function sanitizeNodeAttributes(DOMElement $domElement): void
continue;
}

if (!in_array($attribute->nodeName, $this->allowedAttributes, true)) {
$domElement->removeAttribute($attribute->nodeName);
}
$this->sanitizeNodeAttribute($domElement, $attribute);
}
}

if (in_array($attribute->nodeName, $this->uriAttributes, true)) {
$uri = $this->sanitizeUri((string) $attribute->nodeValue);
/**
* Sanitize a single DOM element attribute
*/
protected function sanitizeNodeAttribute(DOMElement $domElement, DOMAttr $domAttr): void
{
if (!in_array($domAttr->nodeName, $this->allowedAttributes, true)) {
$domElement->removeAttribute($domAttr->nodeName);
}

$scheme = Uri::scheme($uri);
if (in_array($domAttr->nodeName, $this->uriAttributes, true)) {
$uri = $this->sanitizeUri((string) $domAttr->nodeValue);
Comment on lines +243 to +248

if ($scheme === null && !Str::startsWith($uri, '//')) {
continue;
}
$scheme = Uri::scheme($uri);

if (!$this->allowExternalUris || !in_array($scheme, $this->allowedUriSchemes, true)) {
$domElement->removeAttribute($attribute->nodeName);
}
if ($scheme === null && !Str::startsWith($uri, '//')) {
return;
}

if (!$this->allowExternalUris || !in_array($scheme, $this->allowedUriSchemes, true)) {
$domElement->removeAttribute($domAttr->nodeName);
}
}
}
Expand Down
13 changes: 13 additions & 0 deletions formwork/src/Sanitizer/Reference/SvgReference.php
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Original file line number Diff line number Diff line change
Expand Up @@ -318,4 +318,17 @@ class SvgReference
'href',
'xlink:href',
];

/**
* SMIL elements that require handling of the `attributeName` attribute to ensure it is safe
*
* @var list<string>
*/
public const array SMIL_ELEMENTS = [
'animate',
'animateMotion',
'animateTransform',
'discard',
'set',
];
}
27 changes: 27 additions & 0 deletions formwork/src/Sanitizer/SvgSanitizer.php
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,11 @@ class SvgSanitizer extends DomSanitizer

protected array $uriAttributes = SvgReference::URI_ATTRIBUTES;

/**
* @var list<string>
*/
protected array $smilElements = SvgReference::SMIL_ELEMENTS;

public function __construct(
protected DomParserInterface $domParser = new PhpDomParser(),
) {}
Expand All @@ -42,6 +47,19 @@ protected function sanitizeDocumentFragment(DOMDocumentFragment $domDocumentFrag
$this->addExplicitSvgNamespace($domDocumentFragment);
}

protected function sanitizeNodeAttribute(DOMElement $domElement, DOMAttr $domAttr): void
{
parent::sanitizeNodeAttribute($domElement, $domAttr);

if (
in_array($domElement->nodeName, $this->smilElements, true)
&& $domAttr->name === 'attributeName'
&& !$this->isSafeSmilAttributeName($domAttr->value)
) {
$domElement->removeAttribute($domAttr->name);
}
}

protected function addExplicitSvgNamespace(DOMDocumentFragment $domDocumentFragment): void
{
$svg = $domDocumentFragment->firstElementChild;
Expand Down Expand Up @@ -80,4 +98,13 @@ protected function addExplicitSvgNamespace(DOMDocumentFragment $domDocumentFragm

$svg->replaceWith($domElement);
}

/**
* Return whether the SMIL `attributeName` is allowed and not a URI attribute (which would be unsafe)
*/
private function isSafeSmilAttributeName(string $attributeName): bool
{
return in_array($attributeName, $this->allowedAttributes, true)
&& !in_array($attributeName, $this->uriAttributes, true);
}
}
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