\thisispiers\Xss\Escape

A PHP implementation of OWASP's Cross Site Scripting Prevention Cheat Sheet

Released under LGPL v3.0. Requires PHP >= 7.1 and mbstring extension

Install with Composer composer require thisispiers/xss-escape

Usage

Untrusted data should be encoded differently depending on context. This library provides a static method for each context.

Text in HTML Body

i.e. <span>UNTRUSTED DATA</span>

htmlBody(mixed $untrusted_data): string

$untrusted_data is cast to string

HTML in HTML body

i.e. <div>UNTRUSTED HTML</div>

Use a full HTML validator in this context, such as HTML Purifier or DOMPurify

Safe HTML attributes

i.e. <input type="text" name="field_name" value="UNTRUSTED DATA">

htmlAttr(string $attr, mixed $untrusted_data, bool $wrap = true): string

$attr must be one of

• align
• alink
• alt
• bgcolor
• border
• cellpadding
• cellspacing
• class
• color
• cols
• colspan
• coords
• dir
• face
• height
• href (see URLs)
• hspace
• ismap
• lang
• marginheight
• marginwidth
• multiple
• nohref
• noresize
• noshade
• nowrap
• ref
• rel
• rev
• rows
• rowspan
• scrolling
• shape
• span
• src (see URLs)
• summary
• tabindex
• title
• usemap
• valign
• value
• vlink
• vspace
• width

$untrusted_data is cast to string

If $wrap is true, the returned string is prefixed by a space, the attribute name, an equal sign and wrapped in double quote marks i.e. value="ENCODED DATA".

URLs

URLs in src or href HTML attributes i.e. <iframe src="UNTRUSTED URL" /> or <a href="UNTRUSTED URL">link</a>

validateUrl(mixed $untrusted_data): bool

$untrusted_data is cast to string

Untrusted URLs are currently only checked to be HTTPS. This is a crude check to avoid becoming a full URL parsing library. It is highly recommended that you run more sophisticated validation on your untrusted URLs, such as rejecting URLs by hostname.

JavaScript variables

i.e. <script>var someValue='UNTRUSTED DATA';</script> or <script>someFunction('UNTRUSTED DATA');</script>

jsVar(mixed $untrusted_data): string

$untrusted_data is cast to string

CSS values

i.e. <div style="width: UNTRUSTED DATA;">

cssValue(mixed $untrusted_data): string

$untrusted_data is cast to string

URL parameters

i.e. <a href="/site/search?value=UNTRUSTED DATA">link</a>

urlParam(mixed $untrusted_data): string

$untrusted_data is cast to string

JSON in HTML

jsonInHtml(mixed $untrusted_data): string

$untrusted_data is cast to string

Output JSON inside a hidden element before calling JSON.parse e.g.

<div id="data" style="display:none"><?php echo \thisispiers\Xss\Escape::jsonInHtml($untrusted_data); ?></div>
<script>var data = JSON.parse(document.getElementById('data').textContent);</script>

Contributing & Help

Don't expect frequent updates, but pull requests for security and performance improvements are welcome!

There is no guarantee this library complies with the latest OWASP cheat sheet recommendations. Create an issue if you think it's out of date, or start a pull request.

To save keystrokes, you might want to create an alias for this class e.g. class_alias('\\thisispiers\Xss\\Escape', '\\esc');