| 0,0 → 1,85 |
|---|
| <?php |
| |
| /* |
| * Anti XSS |
| * Copyright 2019 Daniel Marschall, ViaThinkSoft |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| // This function prevents XSS, while still allowing the usage of HTML |
| function anti_xss($str, $forbidden_tags=array('script','base','meta','link')) { |
| // Avoid usage of <script tags, but still allow tags that might |
| // have the prefix forbidden tagname as prefix (useful if you want |
| // to block other tags other than "script"). |
| // $str = preg_replace('@<(/{0,1}script[^a-zA-Z])@i', '<\\1', $str); |
| foreach ($forbidden_tags as $tagname) { |
| if ($tagname == '*') { |
| $str = str_replace('<', '<', $str); |
| } else { |
| $str = preg_replace('@<(/{0,1}'.preg_quote($tagname,'@').'[^a-zA-Z])@i', '<\\1', $str); |
| } |
| } |
| |
| if (preg_grep('@^script$@i' , $forbidden_tags)) { |
| // (1) Avoid stuff like a href="javascript:" |
| $str = preg_replace('@(javascript|livescript|vbscript)\s*:@im', '\\1<!-- -->:', $str); |
| |
| // (2) Avoid injection of JavaScript events like onload=, but still allow HTML tags that might start with <on... |
| $str = preg_replace('@O([nN][a-zA-Z]+\s*=)@m', 'O\\1', $str); |
| $str = preg_replace('@o([nN][a-zA-Z]+\s*=)@m', 'o\\1', $str); |
| } |
| |
| return $str; |
| } |
| |
| |
| |
| # Some testcases |
| #echo anti_xss('hallo welt <script>alert(1)</script>'); |
| #echo anti_xss('<svg onload'."\n\n\r\t".'="alert(1)" src=""></svg><online></online> on august ONLINE'); |
| #echo anti_xss('<svg/onload=alert(\'XSS\')>'); |
| #echo '<a href="'.anti_xss('" onclick="alert(1)').'">Click me</a>'; |
| #echo anti_xss('<a href="">foo</a> <abc>xxx</abc>', array('a')); |
| #echo anti_xss('<a href="">foo</a> <abc>xxx</abc>', array('*')); |
| #echo anti_xss("<a href=\"JaVaScRiPt:alert('XSS')\">foobar</a> <pre>JavaScript: is cool</pre>"); |
| #echo anti_xss("<a href=\"JaVaScRiPt : alert('XSS')\">foobar</a> <pre>JavaScript : is cool</pre>"); |
| #echo anti_xss("<a href=\"#\" onclick=\"vbscript:msgbox(\"XSS\")\">foobar</a> <pre>VbScript: is cool</pre>"); |
| #echo anti_xss('<META HTTP-EQUIV="Set-Cookie" Content="USERID=<SCRIPT>alert(\'XSS\')</SCRIPT>">'); |
| |
| # Currently we don't support these XSS vectors. But I am unsure if they work at all, in modern browsers |
| #echo anti_xss('<BR SIZE="&{alert(\'XSS\')}">'); |
| #echo anti_xss('<a href="" onclick="java
script:alert(\'1\')">bla</a>'); |
| |
| # Currently we are vulnerable to this vectors |
| # (does not work with Chrome) |
| #echo anti_xss('<EMBED SRC="data:image/svg+xml;base64,PHN2ZyB4bWxuczpzdmc9Imh0dH A6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcv MjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5L3hs aW5rIiB2ZXJzaW9uPSIxLjAiIHg9IjAiIHk9IjAiIHdpZHRoPSIxOTQiIGhlaWdodD0iMjAw IiBpZD0ieHNzIj48c2NyaXB0IHR5cGU9InRleHQvZWNtYXNjcmlwdCI+YWxlcnQoIlh TUyIpOzwvc2NyaXB0Pjwvc3ZnPg==" type="image/svg+xml" AllowScriptAccess="always"></EMBED>'); |
| #echo anti_xss('<IMG STYLE="xss:expr/*XSS*/ession(alert(\'XSS\'))">'); // only IE |
| |
| # TODO: find more vectors from cheat sheets |
| # https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet |
| |
| /* |
| if (isset($_POST['blabla'])) { |
| echo anti_xss($_POST['blabla']); |
| #echo $_POST['blabla']; |
| } else { |
| |
| echo '<form method="POST" action="anti_xss.php">'; |
| #echo '<textarea name="blabla">'.$_POST['blabla'].'</textarea>'; |
| echo '<textarea name="blabla"></textarea>'; |
| echo '<input type="submit">'; |
| echo '</form>'; |
| } |
| */ |
| |