[FD] CVE-2019-6726: Arbitrary File Deletion in WP fastest Cache <= 0.8.9.0

[Sebastian Neef <fulldisclosure@xxxxxxxxx>]

The wordpress plugin "WP Fastest Cache" [0] suffered from an arbitrary file 
deletion bug. 

# Description

A successful attack allows an unauthenticated attacker to specify a path to a 
directory from which files and directories will be deleted recursively. The 
vulnerable code path extracts the path portion of the referrer header and then 
uses string concatenation to build an absolute path. This path is then passed 
to the 'rm_folder_recursively' function which deletes folders and their files 
in a recursive manner. 

Although a successful exploit leads to data loss and potentially a DoS against 
the website, because wordpress won't find important files to run, there are 
several requirements which need to be met:

- WP Fastest Cache is installed and the cache is activated
- Wordpress is configured to use 'pretty' URL schemes, like /<data>/<title> etc.
- WP Postratings [1] is installed
- At least one ratable post or page was published

# PoC / Exploit

A proof of concept and ready-to-use python exploit script exists at [2], but is 
in general as simple as finding a ratable post/page, extracting the nonce and 
sending a POST request with the malicious referrer header. 

# Timeline
- 24.01.2019: Reported the vulnerability to the vendor
- 24.01.2019: CVE-2019-6726 assigned by MITRE
- 29.01.2019: Finished communication about possible fixes
- 17.02.2019: Vendor released fixed version
- 09.03.2019: Details published

Best,
Sebastian Neef
https://0day.work

[0] https://vi.wordpress.org/plugins/wp-fastest-cache/
[1] https://vi.wordpress.org/plugins/wp-postratings/
[2] 
https://0day.work/cve-2019-6726-arbitrary-file-deletion-in-wp-fastest-cache-0-8-8-1/

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