diff --git a/src/Core/XssSanitiser.php b/src/Core/XssSanitiser.php
new file mode 100644
index 00000000000..5ffdb224b95
--- /dev/null
+++ b/src/Core/XssSanitiser.php
@@ -0,0 +1,213 @@
+sanitiseHtmlValue($htmlValue);
+ return $htmlValue->getContent();
+ }
+
+ /**
+ * Remove XSS attack vectors from HTMLValue content
+ */
+ public function sanitiseHtmlValue(HTMLValue $html): void
+ {
+ foreach ($html->query('//*') as $element) {
+ if (!is_a($element, DOMElement::class)) {
+ continue;
+ }
+ $this->sanitiseElement($element);
+ }
+ }
+
+ /**
+ * Remove XSS attack vectors from a DOMElement
+ */
+ public function sanitiseElement(DOMElement $element): void
+ {
+ // Remove elements first - if we remove the element, we don't have any attributes to check so exit early
+ $removed = $this->stripElement($element);
+ if ($removed) {
+ return;
+ }
+ $this->stripAttributes($element);
+ $this->stripAttributeContents($element);
+ }
+
+ /**
+ * Get the names of elements which will be removed.
+ */
+ public function getElementsToRemove(): array
+ {
+ return $this->elementsToRemove;
+ }
+
+ /**
+ * Set the names of elements which will be removed.
+ * Note that allowing the elements which are included in the default list could result in XSS vulnerabilities.
+ */
+ public function setElementsToRemove(array $elements): static
+ {
+ $this->elementsToRemove = $elements;
+ return $this;
+ }
+
+ /**
+ * Get the names of attributes which will be removed from any elements that have them.
+ */
+ public function getAttributesToRemove(): array
+ {
+ return $this->attributesToRemove;
+ }
+
+ /**
+ * Set the names of attributes which will be removed from any elements that have them.
+ * Note that allowing the attributes which are included in the default list could result in XSS vulnerabilities.
+ */
+ public function setAttributesToRemove(array $attributes): static
+ {
+ $this->attributesToRemove = $attributes;
+ return $this;
+ }
+
+ /**
+ * Get whether the inner contents of an element will be kept for elements that get removed.
+ */
+ public function getKeepInnerHtmlOnRemoveElement(): bool
+ {
+ return $this->keepInnerHtmlOnRemoveElement;
+ }
+
+ /**
+ * Set whether to keep the inner contents of an element if it gets removed.
+ */
+ public function setKeepInnerHtmlOnRemoveElement(bool $keep): static
+ {
+ $this->keepInnerHtmlOnRemoveElement = $keep;
+ return $this;
+ }
+
+ /**
+ * If $element is one of the elements in $elementsToRemove, replace it
+ * with a text node.
+ */
+ private function stripElement(DOMElement $element): bool
+ {
+ if (!in_array($element->tagName, $this->getElementsToRemove())) {
+ return false;
+ }
+ // Make sure we don't remove any child nodes
+ $parentNode = $element->parentNode;
+ if ($this->getKeepInnerHtmlOnRemoveElement() && $parentNode && $element->hasChildNodes()) {
+ // We can't just iterate through $node->childNodes because that seems to skip some children
+ while ($element->hasChildNodes()) {
+ $parentNode->insertBefore($element->firstChild, $element);
+ }
+ }
+ $element->remove();
+ return true;
+ }
+
+ /**
+ * Remove all attributes in $attributesToRemove from the element.
+ */
+ private function stripAttributes(DOMElement $element): void
+ {
+ $attributesToRemove = $this->getAttributesToRemove();
+ if (empty($attributesToRemove)) {
+ return;
+ }
+ $attributes = $element->attributes;
+ for ($i = count($attributes) - 1; $i >= 0; $i--) {
+ /** @var DOMAttr $attr */
+ $attr = $attributes->item($i);
+ foreach ($attributesToRemove as $toRemove) {
+ if (str_starts_with($toRemove, '*') && str_ends_with($attr->name, str_replace('*', '', $toRemove))) {
+ $element->removeAttributeNode($attr);
+ } elseif (str_ends_with($toRemove, '*') && str_starts_with($attr->name, str_replace('*', '', $toRemove))) {
+ $element->removeAttributeNode($attr);
+ } elseif (!str_contains($toRemove, '*') && $attr->name === $toRemove) {
+ $element->removeAttributeNode($attr);
+ }
+ }
+ }
+ }
+
+ /**
+ * Strip out attributes which have dangerous content which might otherwise execute javascript.
+ * This is content that we will always remove regardless of whether the attributes and elements in question
+ * are otherwise allowed, e.g. via WYSIWYG configuration.
+ */
+ private function stripAttributeContents(DOMElement $element): void
+ {
+ $regex = $this->getStripAttributeContentsRegex();
+ foreach (['lowsrc', 'src', 'href', 'data'] as $dangerAttribute) {
+ if ($element->hasAttribute($dangerAttribute)) {
+ $attrContent = $element->getAttribute($dangerAttribute);
+ if (preg_match($regex, $attrContent)) {
+ $element->removeAttribute($dangerAttribute);
+ }
+ }
+ }
+ }
+
+ private function getStripAttributeContentsRegex(): string
+ {
+ $regexes = [
+ $this->splitWithWhitespaceRegex('javascript:'),
+ $this->splitWithWhitespaceRegex('data:text/html'),
+ $this->splitWithWhitespaceRegex('vbscript:'),
+ ];
+ // Regex is "starts with any of these, with optional whitespace at the start, case insensitive"
+ return '#^\s*(' . implode('|', $regexes) . ')#iu';
+ }
+
+ private function splitWithWhitespaceRegex(string $string): string
+ {
+ // Note that `\s` explicitly includes ALL invisible characters when used with the `u` modifier.
+ // That includes unicode characters like the non-breaking space.
+ return implode('\s*', str_split($string));
+ }
+}
diff --git a/src/Forms/FormMessage.php b/src/Forms/FormMessage.php
index ce18ee153a6..8a6d85b74a3 100644
--- a/src/Forms/FormMessage.php
+++ b/src/Forms/FormMessage.php
@@ -3,6 +3,7 @@
namespace SilverStripe\Forms;
use InvalidArgumentException;
+use SilverStripe\Core\XssSanitiser;
use SilverStripe\ORM\ValidationResult;
use SilverStripe\View\ViewableData;
@@ -33,6 +34,7 @@ trait FormMessage
/**
* Returns the field message, used by form validation.
+ * If the current cast is ValidationResult::CAST_HTML, the message will be sanitised.
*
* Use {@link setError()} to set this property.
*
@@ -40,7 +42,11 @@ trait FormMessage
*/
public function getMessage()
{
- return $this->message;
+ $message = $this->message;
+ if ($this->getMessageCast() === ValidationResult::CAST_HTML) {
+ $message = XssSanitiser::create()->sanitiseString($message);
+ }
+ return $message;
}
/**
diff --git a/src/Forms/HTMLEditor/HTMLEditorSanitiser.php b/src/Forms/HTMLEditor/HTMLEditorSanitiser.php
index c056bca10f3..49eda400afa 100644
--- a/src/Forms/HTMLEditor/HTMLEditorSanitiser.php
+++ b/src/Forms/HTMLEditor/HTMLEditorSanitiser.php
@@ -6,6 +6,7 @@
use DOMElement;
use SilverStripe\Core\Config\Configurable;
use SilverStripe\Core\Injector\Injectable;
+use SilverStripe\Core\XssSanitiser;
use SilverStripe\View\Parsers\HTMLValue;
use stdClass;
@@ -289,6 +290,10 @@ public function sanitise(HTMLValue $html)
{
$linkRelValue = $this->config()->get('link_rel_value');
$doc = $html->getDocument();
+ // Get a sanitiser but don't deny any specific attributes or elements, since that's
+ // handled as part of the element rules.
+ $xssSanitiser = XssSanitiser::create();
+ $xssSanitiser->setElementsToRemove([])->setAttributesToRemove([]);
/** @var DOMElement $el */
foreach ($html->query('//body//*') as $el) {
@@ -342,16 +347,8 @@ public function sanitise(HTMLValue $html)
$el->setAttribute($attr, $forced);
}
- // Matches "javascript:" with any arbitrary linebreaks inbetween the characters.
- $regex = '#^\s*(' . implode('\s*', str_split('javascript:')) . '|' . implode('\s*', str_split('data:text/html;')) . ')#i';
- // Strip out javascript execution in href or src attributes.
- foreach (['src', 'href', 'data'] as $dangerAttribute) {
- if ($el->hasAttribute($dangerAttribute)) {
- if (preg_match($regex, $el->getAttribute($dangerAttribute))) {
- $el->removeAttribute($dangerAttribute);
- }
- }
- }
+ // Explicit XSS sanitisation for anything that there's really no sensible use case for in a WYSIWYG
+ $xssSanitiser->sanitiseElement($el);
}
if ($el->tagName === 'a' && $linkRelValue !== null) {
diff --git a/tests/php/Core/XssSanitiserTest.php b/tests/php/Core/XssSanitiserTest.php
new file mode 100644
index 00000000000..0d1ef959447
--- /dev/null
+++ b/tests/php/Core/XssSanitiserTest.php
@@ -0,0 +1,463 @@
+ '',
+ 'expected' => '',
+ ],
+ [
+ 'input' => 'hello world',
+ 'expected' => 'hello world',
+ ],
+ [
+ 'input' => '<hello world>',
+ 'expected' => '<hello world>',
+ ],
+ [
+ 'input' => '< Hello',
+ 'expected' => ' Hello',
+ ],
+ [
+ 'input' => 'Lorem & Ipsum',
+ 'expected' => 'Lorem & Ipsum',
+ ],
+ // Unknown tag
+ [
+ 'input' => 'Lorem ipsum',
+ 'expected' => 'Lorem ipsum',
+ ],
+ // Scripts
+ [
+ 'input' => '',
+ 'expected' => 'alert(\'ok\');',
+ ],
+ [
+ 'input' => 'javascript:/*-->