DokuWiki 2018-04-22a Greebo Arbitrary Code Execution

`SEC Consult Vulnerability Lab Security Advisory < 20180906-0 >  
=======================================================================  
title: CSV Formula Injection  
product: DokuWiki  
vulnerable version: 2018-04-22a "Greebo" and older versions  
fixed version: None  
CVE number: CVE-2018-15474  
impact: Medium  
homepage: https://www.dokuwiki.org  
found: 2018-07-09  
by: Jean-Benjamin Rousseau (Office Zurich)  
SEC Consult Vulnerability Lab  
  
An integrated part of SEC Consult  
Europe | Asia | North America  
  
https://www.sec-consult.com  
  
=======================================================================  
  
Vendor description:  
-------------------  
"DokuWiki is a simple to use and highly versatile Open Source wiki software  
that doesn't require a database. It is loved by users for its clean and  
readable syntax. The ease of maintenance, backup and integration makes it  
an administrator's favorite. Built in access controls and authentication  
connectors make DokuWiki especially useful in the enterprise context  
and the large number of plugins contributed by its vibrant community allow  
for a broad range of use cases beyond a traditional wiki."  
  
Source: https://www.dokuwiki.org/dokuwiki  
  
  
Business recommendation:  
------------------------  
The issue will not be fixed according to the vendor. Users are advised  
to be careful when opening files via the CSV export functionality.  
  
SEC Consult recommends to perform a thorough security review conducted by  
security professionals to identify and resolve all security issues.  
  
  
Vulnerability overview/description:  
-----------------------------------  
1) CSV Formula Injection vulnerability  
The administration panel of the application has a "CSV export of users"  
feature which allows the export of user data (username, real name,  
email address and user groups) as a CSV file. On the registration page,  
it is possible for an attacker to set certain values in the Real Name field  
that - when exported and opened with a spreadsheet application  
(Microsoft Excel, Open Office, etc.) - will be interpreted as a formula.  
This puts the administrators who open those malicious exported files at risk.  
Exfiltration of sensitive data or even the execution of arbitrary code  
on the local machine of the victim will be the result. The final impact  
depends on the used spreadsheet software on the client of the victim.  
  
  
Proof of concept:  
-----------------  
1) CSV Formula Injection vulnerability  
Registration URL:  
http://www.example.com/doku.php?id=start&do=register  
  
When the registration request is submitted, the following parameters are sent  
in a POST request:  
  
sectok=&do=register&save=1&login=login_parameter&fullname=evil_csv_formula_injection_payload&email=email_address  
  
The "fullname" parameter is not sanitized before being stored and during  
the CSV export. An attacker can inject different CSV formula  
payloads in the fullname parameter.  
For example:  
=cmd|'/C calc'!A0  
  
As soon as the file gets opened in Microsoft Excel, the program calc.exe is  
launched. Different warnings might pop up. However, these warnings are usually  
ignored because the file comes from a trusted source.  
  
  
Vulnerable / tested versions:  
-----------------------------  
The latest version 2018-04-22a "Greebo" has been tested:  
https://download.dokuwiki.org/out/dokuwiki-8a269cc015a64b40e4c918699f1e1142.tgz  
  
Also found to be vulnerable:  
2017-02-19 stable release  
2016-06-26 stable release  
2015-08-10 stable release  
2014-09-29 stable release  
2014-05-05 stable release  
2013-12-08 stable release  
  
  
Vendor contact timeline:  
------------------------  
2018-07-18: Contacting vendor through [email protected]  
2018-07-18: Vendor replied, they asked for the advisory without encryption  
2018-07-19: Advisory sent without encryption  
2018-07-19: Vendor replied with no intention to fix the vulnerability  
2018-07-30: Reminder sent to the vendor. No reply  
2018-08-20: Ask for updates to the vendor  
2018-08-20: Vendor replied that no patch will be provided  
2018-09-06: Public release of security advisory  
  
  
Solution:  
---------  
The issue will not be fixed according to the vendor:  
https://github.com/splitbrain/dokuwiki/issues/2450  
  
  
Workaround:  
-----------  
None  
  
  
Advisory URL:  
-------------  
https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html  
  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
SEC Consult Vulnerability Lab  
  
SEC Consult  
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EOF Jean-Benjamin Rousseau / @2018  
  
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