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Merge pull request #495 from aidantwoods/anti-xss

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Prevent various XSS attacks [rebase and update of #276]
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Emanuil Rusev 2018-02-28 13:41:37 +02:00 committed by GitHub
commit 6678d59be4
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8 changed files with 195 additions and 17 deletions
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123
Parsedown.php
View File

@ -75,6 +75,32 @@ class Parsedown
protected $urlsLinked = true;
function setSafeMode($safeMode)
{
$this->safeMode = (bool) $safeMode;
return $this;
}
protected $safeMode;
protected $safeLinksWhitelist = array(
'http://',
'https://',
'ftp://',
'ftps://',
'mailto:',
'data:image/png;base64,',
'data:image/gif;base64,',
'data:image/jpeg;base64,',
'irc:',
'ircs:',
'git:',
'ssh:',
'news:',
'steam:',
);
#
# Lines
#
@ -342,8 +368,6 @@ class Parsedown
{
$text = $Block['element']['text']['text'];
$text = htmlspecialchars($text, ENT_NOQUOTES, 'UTF-8');
$Block['element']['text']['text'] = $text;
return $Block;
@ -354,7 +378,7 @@ class Parsedown
protected function blockComment($Line)
{
if ($this->markupEscaped)
if ($this->markupEscaped or $this->safeMode)
{
return;
}
@ -457,8 +481,6 @@ class Parsedown
{
$text = $Block['element']['text']['text'];
$text = htmlspecialchars($text, ENT_NOQUOTES, 'UTF-8');
$Block['element']['text']['text'] = $text;
return $Block;
@ -678,7 +700,7 @@ class Parsedown
protected function blockMarkup($Line)
{
if ($this->markupEscaped)
if ($this->markupEscaped or $this->safeMode)
{
return;
}
@ -1074,7 +1096,6 @@ class Parsedown
if (preg_match('/^('.$marker.'+)[ ]*(.+?)[ ]*(?<!'.$marker.')\1(?!'.$marker.')/s', $Excerpt['text'], $matches))
{
$text = $matches[2];
$text = htmlspecialchars($text, ENT_NOQUOTES, 'UTF-8');
$text = preg_replace("/[ ]*\n/", ' ', $text);
return array(
@ -1253,8 +1274,6 @@ class Parsedown
$Element['attributes']['title'] = $Definition['title'];
}
$Element['attributes']['href'] = str_replace(array('&', '<'), array('&amp;', '&lt;'), $Element['attributes']['href']);
return array(
'extent' => $extent,
'element' => $Element,
@ -1263,7 +1282,7 @@ class Parsedown
protected function inlineMarkup($Excerpt)
{
if ($this->markupEscaped or strpos($Excerpt['text'], '>') === false)
if ($this->markupEscaped or $this->safeMode or strpos($Excerpt['text'], '>') === false)
{
return;
}
@ -1343,14 +1362,16 @@ class Parsedown
if (preg_match('/\bhttps?:[\/]{2}[^\s<]+\b\/*/ui', $Excerpt['context'], $matches, PREG_OFFSET_CAPTURE))
{
$url = $matches[0][0];
$Inline = array(
'extent' => strlen($matches[0][0]),
'position' => $matches[0][1],
'element' => array(
'name' => 'a',
'text' => $matches[0][0],
'text' => $url,
'attributes' => array(
'href' => $matches[0][0],
'href' => $url,
),
),
);
@ -1363,7 +1384,7 @@ class Parsedown
{
if (strpos($Excerpt['text'], '>') !== false and preg_match('/^<(\w+:\/{2}[^ >]+)>/i', $Excerpt['text'], $matches))
{
$url = str_replace(array('&', '<'), array('&amp;', '&lt;'), $matches[1]);
$url = $matches[1];
return array(
'extent' => strlen($matches[0]),
@ -1401,6 +1422,11 @@ class Parsedown
protected function element(array $Element)
{
if ($this->safeMode)
{
$Element = $this->sanitiseElement($Element);
}
$markup = '<'.$Element['name'];
if (isset($Element['attributes']))
@ -1412,7 +1438,7 @@ class Parsedown
continue;
}
$markup .= ' '.$name.'="'.$value.'"';
$markup .= ' '.$name.'="'.self::escape($value).'"';
}
}
@ -1426,7 +1452,7 @@ class Parsedown
}
else
{
$markup .= $Element['text'];
$markup .= self::escape($Element['text'], true);
}
$markup .= '</'.$Element['name'].'>';
@ -1485,10 +1511,77 @@ class Parsedown
return $markup;
}
protected function sanitiseElement(array $Element)
{
static $goodAttribute = '/^[a-zA-Z0-9][a-zA-Z0-9-_]*+$/';
static $safeUrlNameToAtt = array(
'a' => 'href',
'img' => 'src',
);
if (isset($safeUrlNameToAtt[$Element['name']]))
{
$Element = $this->filterUnsafeUrlInAttribute($Element, $safeUrlNameToAtt[$Element['name']]);
}
if ( ! empty($Element['attributes']))
{
foreach ($Element['attributes'] as $att => $val)
{
# filter out badly parsed attribute
if ( ! preg_match($goodAttribute, $att))
{
unset($Element['attributes'][$att]);
}
# dump onevent attribute
elseif (self::striAtStart($att, 'on'))
{
unset($Element['attributes'][$att]);
}
}
}
return $Element;
}
protected function filterUnsafeUrlInAttribute(array $Element, $attribute)
{
foreach ($this->safeLinksWhitelist as $scheme)
{
if (self::striAtStart($Element['attributes'][$attribute], $scheme))
{
return $Element;
}
}
$Element['attributes'][$attribute] = str_replace(':', '%3A', $Element['attributes'][$attribute]);
return $Element;
}
#
# Static Methods
#
protected static function escape($text, $allowQuotes = false)
{
return htmlspecialchars($text, $allowQuotes ? ENT_NOQUOTES : ENT_QUOTES, 'UTF-8');
}
protected static function striAtStart($string, $needle)
{
$len = strlen($needle);
if ($len > strlen($string))
{
return false;
}
else
{
return strtolower(substr($string, 0, $len)) === strtolower($needle);
}
}
static function instance($name = 'default')
{
if (isset(self::$instances[$name]))

2
test/ParsedownTest.php
View File

@ -48,6 +48,8 @@ class ParsedownTest extends TestCase
$expectedMarkup = str_replace("\r\n", "\n", $expectedMarkup);
$expectedMarkup = str_replace("\r", "\n", $expectedMarkup);
$this->Parsedown->setSafeMode(substr($test, 0, 3) === 'xss');
$actualMarkup = $this->Parsedown->text($markdown);
$this->assertEquals($expectedMarkup, $actualMarkup);

6
test/data/xss_attribute_encoding.html Normal file
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@ -0,0 +1,6 @@
<p><a href="https://www.example.com&quot;">xss</a></p>
<p><img src="https://www.example.com&quot;" alt="xss" /></p>
<p><a href="https://www.example.com&#039;">xss</a></p>
<p><img src="https://www.example.com&#039;" alt="xss" /></p>
<p><img src="https://www.example.com" alt="xss&quot;" /></p>
<p><img src="https://www.example.com" alt="xss&#039;" /></p>

11
test/data/xss_attribute_encoding.md Normal file
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@ -0,0 +1,11 @@
[xss](https://www.example.com")
![xss](https://www.example.com")
[xss](https://www.example.com')
![xss](https://www.example.com')
![xss"](https://www.example.com)
![xss'](https://www.example.com)

16
test/data/xss_bad_url.html Normal file
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@ -0,0 +1,16 @@
<p><a href="javascript%3Aalert(1)">xss</a></p>
<p><a href="javascript%3Aalert(1)">xss</a></p>
<p><a href="javascript%3A//alert(1)">xss</a></p>
<p><a href="javascript&amp;colon;alert(1)">xss</a></p>
<p><img src="javascript%3Aalert(1)" alt="xss" /></p>
<p><img src="javascript%3Aalert(1)" alt="xss" /></p>
<p><img src="javascript%3A//alert(1)" alt="xss" /></p>
<p><img src="javascript&amp;colon;alert(1)" alt="xss" /></p>
<p><a href="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
<p><a href="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
<p><a href="data%3A//text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
<p><a href="data&amp;colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
<p><img src="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
<p><img src="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
<p><img src="data%3A//text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
<p><img src="data&amp;colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>

31
test/data/xss_bad_url.md Normal file
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@ -0,0 +1,31 @@
[xss](javascript:alert(1))
[xss]( javascript:alert(1))
[xss](javascript://alert(1))
[xss](javascript&colon;alert(1))
![xss](javascript:alert(1))
![xss]( javascript:alert(1))
![xss](javascript://alert(1))
![xss](javascript&colon;alert(1))
[xss](data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
[xss]( data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
[xss](data://text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
[xss](data&colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
![xss](data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
![xss]( data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
![xss](data://text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)
![xss](data&colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==)

7
test/data/xss_text_encoding.html Normal file
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@ -0,0 +1,7 @@
<p>&lt;script&gt;alert(1)&lt;/script&gt;</p>
<p>&lt;script&gt;</p>
<p>alert(1)</p>
<p>&lt;/script&gt;</p>
<p>&lt;script&gt;
alert(1)
&lt;/script&gt;</p>

12
test/data/xss_text_encoding.md Normal file
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@ -0,0 +1,12 @@
<script>alert(1)</script>
<script>
alert(1)
</script>
<script>
alert(1)
</script>