Active formatting elements

Find "active formatting elements" that get duplicated in case of wrongly nested tags

Created May 1, 2024

Updated May 27, 2025

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CategoryHTML Parsing

VisibilityPublic

TypeXSS

CharsetUTF-8

$[data1] placeholderhtml

Template used:

<p><$[data1] class="class">a<p>b</p>c</$[data1]></p>

Code used after fuzz:

if (document.getElementsByClassName("class").length > 1) log('$[data1]')

Sample payloads

<p><a class="class">a<p>b</p>c</a></p>

<p><b class="class">a<p>b</p>c</b></p>

<p><big class="class">a<p>b</p>c</big></p>

<p><code class="class">a<p>b</p>c</code></p>

<p><em class="class">a<p>b</p>c</em></p>

<p><font class="class">a<p>b</p>c</font></p>

<p><i class="class">a<p>b</p>c</i></p>

<p><nobr class="class">a<p>b</p>c</nobr></p>

<p><s class="class">a<p>b</p>c</s></p>

<p><small class="class">a<p>b</p>c</small></p>

<p><strike class="class">a<p>b</p>c</strike></p>

<p><strong class="class">a<p>b</p>c</strong></p>

<p><tt class="class">a<p>b</p>c</tt></p>

<p><u class="class">a<p>b</p>c</u></p>