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These types of attacks has been introduced and documented [**by Orange in this blog post**](https://blog.orange.tw/2024/08/confusion-attacks-en.html?m=1) and the following is a summary. The "confusion" attack basically abuses how the tens of modules that work together creating a Apache don't work perfectly synchronised and making some of them modify some unexpected data can cause a vulnerability in a later module.
### Filename Confusion
#### Truncation
The **`mod_rewrite`** will trim the content of `r->filename` after the character `?` ([_**modules/mappers/mod\_rewrite.c#L4141**_](https://github.com/apache/httpd/blob/2.4.58/modules/mappers/mod\_rewrite.c#L4141)). This isn't totally wrong as most modules will treat `r->filename` as an URL. Bur in other occasions this will be treated as file path, which would cause a problem.
* **Path Truncation**
It's possible to abuse `mod_rewrite` like in the following rule example to access other files inside the file system, removing the last part of the expected path adding simply a `?`:
# the output of file `/var/user/orange/profile.yml`
# Attack
curl http://server/user/orange%2Fsecret.yml%3F
#the output of file `/var/user/orange/secret.yml`
```
* **Mislead RewriteFlag Assignment**
In the following rewrite rule, as long as the URL ends in .php it's going to be treated and executed as php. Therefore, it's possible send a URL that ends in .php after the `?` char while loading in the path a different type of file (like an image) with malicious php code inside of it:
It's possible to access files the user shouldn't be able to access even if the access should be denied with configurations like:
```xml
<Files"admin.php">
AuthType Basic
AuthName "Admin Panel"
AuthUserFile "/etc/apache2/.htpasswd"
Require valid-user
</Files>
```
This is because by default PHP-FPM will receive URLs ending in `.php`, like `http://server/admin.php%3Fooo.php` and because PHP-FPM will remove anything after the character `?`, the previous URL will allow to load `/admin.php` even if the previous rule prohibited it.
### DocumentRoot Confusion
```bash
DocumentRoot /var/www/html
RewriteRule ^/html/(.*)$ /$1.html
```
A fun fact about Apache is that the previous rewrite will try to access the file from both the documentRoot and from root. So, a request to `https://server/abouth.html` will check for the file in `/var/www/html/about.html` and `/about.html` in the file system. Which basically can be abused to access files in the file system.
#### **Server-Side Source Code Disclosure**
* **Disclose CGI Source Code**
Just adding a %3F at the end is enough to leak the source code of a cgi module:
The main problem with the previous attack is that by default most access over the filesystem will be denied as in Apache HTTP Server’s [configuration template](https://github.com/apache/httpd/blob/trunk/docs/conf/httpd.conf.in#L115):
```xml
<Directory/>
AllowOverride None
Require all denied
</Directory>
```
However, [Debian/Ubuntu](https://sources.debian.org/src/apache2/2.4.62-1/debian/config-dir/apache2.conf.in/#L165) operating systems by default allow `/usr/share`:
```xml
<Directory/usr/share>
AllowOverride None
Require all granted
</Directory>
```
Therefore, it would be possible to **abuse files located inside `/usr/share` in these distributions.**
**Local Gadget to Information Disclosure**
* **Apache HTTP Server** with **websocketd** may expose the **dump-env.php** script at **/usr/share/doc/websocketd/examples/php/**, which can leak sensitive environment variables.
* Servers with **Nginx** or **Jetty** might expose sensitive web application information (e.g., **web.xml**) through their default web roots placed under **/usr/share**:
* **/usr/share/nginx/html/**
* **/usr/share/jetty9/etc/**
* **/usr/share/jetty9/webapps/**
**Local Gadget to XSS**
* On Ubuntu Desktop with **LibreOffice installed**, exploiting the help files' language switch feature can lead to **Cross-Site Scripting (XSS)**. Manipulating the URL at **/usr/share/libreoffice/help/help.html** can redirect to malicious pages or older versions through **unsafe RewriteRule**.
**Local Gadget to LFI**
* If PHP or certain front-end packages like **JpGraph** or **jQuery-jFeed** are installed, their files can be exploited to read sensitive files like **/etc/passwd**:
* Utilizing **MagpieRSS's magpie\_debug.php** at **/usr/share/php/magpierss/scripts/magpie\_debug.php**, an SSRF vulnerability can be easily created, providing a gateway to further exploits.
**Local Gadget to RCE**
* Opportunities for **Remote Code Execution (RCE)** are vast, with vulnerable installations like an outdated **PHPUnit** or **phpLiteAdmin**. These can be exploited to execute arbitrary code, showcasing the extensive potential of local gadgets manipulation.
#### **Jailbreak from Local Gadgets**
It's also possible to jailbreak from the allowed folders by following symlinks generated by installed software in those folders, like:
This attack exploits the overlap in functionality between the `AddHandler` and `AddType` directives, which both can be used to **enable PHP processing**. Originally, these directives affected different fields (`r->handler` and `r->content_type` respectively) in the server's internal structure. However, due to legacy code, Apache handles these directives interchangeably under certain conditions, converting `r->content_type` into `r->handler` if the former is set and the latter is not.
Moreover, in the Apache HTTP Server (`server/config.c#L420`), if `r->handler` is empty before executing `ap_run_handler()`, the server **uses `r->content_type` as the handler**, effectively making `AddType` and `AddHandler` identical in effect.
#### **Overwrite Handler to Disclose PHP Source Code**
In [**this talk**](https://web.archive.org/web/20210909012535/https://zeronights.ru/wp-content/uploads/2021/09/013\_dmitriev-maksim.pdf), was presented a vulnerability where an incorrect `Content-Length` sent by a client can cause Apache to mistakenly **return the PHP source code**. This was because an error handling issue with ModSecurity and the Apache Portable Runtime (APR), where a double response leads to overwriting `r->content_type` to `text/html`.\
Because ModSecurity doesn't properly handle return values, it would return the PHP code and won't interpret it.
#### **Overwrite Handler to XXXX**
TODO: Orange hasn't disclose this vulnerability yet
### **Invoke Arbitrary Handlers**
If an attacker is able to control the **`Content-Type`** header in a server response he is going to be able to **invoke arbitrary module handlers**. However, by the point the attacker controls this, most of the process of the request will be done. However, it's possible to **restart the request process abusing the `Location` header** because if the **r**eturned `Status` is 200 and the `Location` header starts with a `/`, the response is treated as a Server-Side Redirection and should be processed
According to [RFC 3875](https://datatracker.ietf.org/doc/html/rfc3875) (specification about CGI) in [Section 6.2.2](https://datatracker.ietf.org/doc/html/rfc3875#section-6.2.2) defines a Local Redirect Response behavior:
> The CGI script can return a URI path and query-string (‘local-pathquery’) for a local resource in a Location header field. This indicates to the server that it should reprocess the request using the path specified.
Therefore, to perform this attack is needed one of the following vulns:
* CRLF Injection in the CGI response headers
* SSRF with complete control of the response headers
#### **Arbitrary Handler to Information Disclosure**
For example `/server-status` should only be accessible locally:
```xml
<Location/server-status>
SetHandler server-status
Require local
</Location>
```
It's possible to access it setting the `Content-Type` to `server-status` and the Location header starting with `/`
```
http://server/cgi-bin/redir.cgi?r=http:// %0d%0a
Location:/ooo %0d%0a
Content-Type:server-status %0d%0a
%0d%0a
```
#### **Arbitrary Handler to Full SSRF**
Redirecting to `mod_proxy` to access any protocol on any URL:
```
http://server/cgi-bin/redir.cgi?r=http://%0d%0a
Location:/ooo %0d%0a
Content-Type:proxy:
http://example.com/%3F
%0d%0a
%0d%0a
```
However, the `X-Forwarded-For` header is added preventing access to cloud metadata endpoints.
#### **Arbitrary Handler to Access Local Unix Domain Socket**
Access PHP-FPM’s local Unix Domain Socket to execute a PHP backdoor located in `/tmp/`:
The official [PHP Docker](https://hub.docker.com/\_/php) image includes PEAR (`Pearcmd.php`), a command-line PHP package management tool, which can be abused to obtain RCE:
Check [**Docker PHP LFI Summary**](https://www.leavesongs.com/PENETRATION/docker-php-include-getshell.html#0x06-pearcmdphp), written by [Phith0n](https://x.com/phithon\_xg) for the details of this technique.
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