Arbitrary file deletion vulnerability in Image Slider allows authenticated users to delete files (WordPress plugin)

[dxw Security <security () dxw com>]

Details
================
Software: Image Slider
Version: 1.1.41,1.1.89
Homepage: http://wordpress.org/plugins/image-slider-widget/
Advisory report: 
https://security.dxw.com/advisories/arbitrary-file-deletion-vulnerability-in-image-slider-allows-authenticated-users-to-delete-files/
CVE: Awaiting assignment
CVSS: 5.5 (Medium; AV:N/AC:L/Au:S/C:P/I:P/A:N)

Description
================
Arbitrary file deletion vulnerability in Image Slider allows authenticated users to delete files

Vulnerability
================
Any user able to create or edit “Sliders” (the same users who can create/edit posts, as far as I can tell) is able to 
delete arbitrary files that the web user has permission to write to. In addition, the attacker is told whether that 
operation succeeded or failed.
Depending on configuration this could lead to the attacker being able to:

Delete media uploads
Delete plugin files (this would be especially bad if there were security plugins limiting the attacker’s abilities)
Delete important system files (/etc/hosts, /usr/bin/php)
Attempt to delete unimportant files in order to discover more information about the system (i.e. attempting to delete 
/usr/share/doc/apt/changelog.gz would have little effect on the system if successful but it would tell the attacker 
that the host is running a Debian derivative)


Proof of concept
================

First, make sure you have a file to delete. I’m going to use /etc/hosts as an example because it demonstrates that 
you’re not limited to files within the WordPress installation, but make sure whichever file you use can be deleted by 
the user account WordPress is running under
Visit /wp-admin/post-new.php?post_type=easyimageslider
Input the following JavaScript in the inspector’s console to get the nonce value: 
document.querySelector(\'[data-tnonce]\').dataset[\'tnonce\']
Create a page containing the following code, replace NONCE with the nonce you got in the previous step, visit the page 
and click submit

<form action=\"http://localhost/wp-admin/admin-ajax.php\"; method=\"POST\">
  <input type=\"text\" name=\"action\" value=\"ewic_timthumb_check\">
  <input type=\"text\" name=\"turl\" value=\"/etc/hosts\">
  <input type=\"text\" name=\"security\" value=\"NONCE\">
  <input type=\"submit\">
</form>
If WordPress is being run as root (or if the web user has permission to write to that file) then the page will display 
“1”, if not it won’t display anything.

Mitigations
================
Disable the plugin. No fixed version is known.

Disclosure policy
================
dxw believes in responsible disclosure. Your attention is drawn to our disclosure policy: 
https://security.dxw.com/disclosure/

Please contact us on security () dxw com to acknowledge this report if you received it via a third party (for example, 
plugins () wordpress org) as they generally cannot communicate with us on your behalf.

This vulnerability will be published if we do not receive a response to this report with 14 days.

Timeline
================

2015-10-29: Discovered
2016-12-09: Reported to vendor via info () ghozylab com
2016-12-23: Vendor has not responded after 14 days
2016-12-23: Published



Discovered by dxw:
================
Tom Adams
Please visit security.dxw.com for more information.
          


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