diff --git a/README.md b/README.md index 2f65e56..1b629e6 100644 --- a/README.md +++ b/README.md @@ -38,7 +38,32 @@ More examples in [the wiki](https://github.com/erusev/parsedown/wiki/) and in [t ### Security -Parsedown does not sanitize the HTML that it generates. When you deal with untrusted content (ex: user comments) you should also use a HTML sanitizer like [HTML Purifier](http://htmlpurifier.org/). +Parsedown is capable of escaping user-input within the HTML that it generates. Additionally Parsedown will apply sanitisation to additional scripting vectors (such as scripting link destinations) that are introduced by the markdown syntax itself. + +To tell Parsedown that it is processing untrusted user-input, use the following: +```php +$parsedown = new Parsedown; +$parsedown->setSafeMode(true); +``` + +If instead, you wish to allow HTML within untrusted user-input, but still want output to be free from XSS it is recommended that you make use of a HTML sanitiser that allows HTML tags to be whitelisted, like [HTML Purifier](http://htmlpurifier.org/). + +In both cases you should strongly consider employing defence-in-depth measures, like [deploying a Content-Secuity-Policy](https://scotthelme.co.uk/content-security-policy-an-introduction/) (making use of browser security feature) so that your page is likely to be safe even if an attacker finds a vulnerability in one of the first lines of defence above. + +#### Security of Parsedown Extensions + +Safe mode does not necessarily yield safe results when using extensions to Parsedown. Extensions should be evaluated on their own to determine their specific safety against XSS. + +### Escaping HTML +> ⚠️  **WARNING:** This method isn't safe from XSS! + +If you wish to escape HTML **in trusted input**, you can use the following: +```php +$parsedown = new Parsedown; +$parsedown->setMarkupEscaped(true); +``` + +Beware that this still allows users to insert unsafe scripting vectors, such as links like `[xss](javascript:alert%281%29)`. ### Questions