(Pentest Apache #2) - The Beauty of "%3F" and Apache's Inability | Wordpress | Mod Security

Tested Apache Version: Apache 1.3.37(Unix) (with different modules)

I was doing an open research and came across an interesting issue which helps a penetration tester to gather more information about the files present (directory listing) on the web server (specific web folder). I tested only one version of Apache for this. Let's understand this issue. The problem is present in Apache's ability to process the encoded value of "?" which is "%3F". 

Testing: During the validation, I found that wordpress was running on Apache 1.3.37(unix). Due to misconfiguration, it was possible to access the /wp-includes/  folder, which resulted in directory listing as shown below:

So, when I accessed the /wp-admin/ directory, it redirected me to the login page as presented below:

Tthe above presented screenshot shows the correct behavior of the wordpress or the Apache server when /wp-admin/ directory is accessed. Now, when I accessed the http://www.example.com/blog/ , the web server displayed the contents of wordpress blog such as posts and entries. 

Question : Is it possible to get the directory listing on accessing the /blog/ directory?

Answer : Yes, It can be done in some web servers such as Apache.

Question : How can it be possible?

Answer : I exploited the behavior of Apache in processing the encoded "?" character whose value is

"%3F". Amazingly, it worked. I constructed the payload as:   http://www.example.com/blog/%3Fpage_id=34. [One can use any id number or parameter]

Other examples:

http://www.example.com/blog/%3Fp_id=34

http://www.example.com/blog/%3Fpg_id=34

When I used the above stated payload, I got the response as follows:

This allowed me to get the listing of the /blog/ directory which really helped me to understand the presence of different files on the remote web server. But, If I used the payload as: http://www.example.com/blog/?page_id=34 without encoding, it did not work. So the encoding of "?" character resulted in failure of processing the request as desired by the Apache web server thereby resulting in directory listing.

Let's have a look at the HTTP response headers:

Request 1: http://www.example.com/blog/%3Fpage_id=34.

(Status-Line)      HTTP/1.1 200 OK
Date      Sun, 20 Jan 2013 19:22:59 GMT
Server   VHFFS / Apache/1.3.34 (Unix) mod_lo/1.0 PHP/4.4.4 with Hardening-Patch mod_ssl/2.8.25 OpenSSL/0.9.8b mod_chroot/0.5
Content-Type    text/html; charset=ISO-8859-1
Transfer-Encoding           chunked

Request 2: http://www.example.com/blog/?page_id=34

(Status-Line)      HTTP/1.1 200 OK
Date      Sun, 20 Jan 2013 19:23:48 GMT
Server   VHFFS / Apache/1.3.34 (Unix) mod_lo/1.0 PHP/4.4.4 with Hardening-Patch mod_ssl/2.8.25 OpenSSL/0.9.8b mod_chroot/0.5
X-Powered-By  PHP/5.1.5 with Hardening-Patch
Content-Type    text/html; charset=ISO-8859-1
Transfer-Encoding           chunked

In the request 2, the response contains X-Powered-By as compared to the first request. So, the PHP preprocessor plays a part in it.

Constraint: In this technique, one can only get the directory listing but will no be able to access those files

until unless there is misconfiguration issue.

Background: I forced Google to provide me with related information and I got the related links as follows:

1. http://stackoverflow.com/questions/9786853/apache-not-processing-encoded-urls-with-3f

2. https://issues.apache.org/bugzilla/show_bug.cgi?id=34602

Solution: Configure appropriate rewrite rules using mod_rewrite to prevent these types of vulnerabilities.

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Note: If any reader has a specific view on this, please respond back.