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Test HTTP Methods
HTTP offers a number of methods that can be used to perform actions on the web server (the HTTP 1.1 standard refers to them as
methods but they are also commonly described as
verbs). While GET and POST are by far the most common methods that are used to access information provided by a web server, HTTP allows several other (and somewhat less known) methods. Some of these can be used for nefarious purposes if the web server is misconfigured.
RFC 7231 – Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content defines the following valid HTTP request methods, or verbs:
However, most web applications only need to respond to GET and POST requests, receiving user data in the URL query string or appended to the request respectively. The standard
<a href=""></a> style links as well as forms defined without a method trigger a GET request; form data submitted via
- Test supported HTTP methods.
- Test for access control bypass.
- Test XST vulnerabilities.
- Test HTTP method overriding techniques.
How to Test
Discover the Supported Methods
To perform this test, the tester needs some way to figure out which HTTP methods are supported by the web server that is being examined. While the
OPTIONS HTTP method provides a direct way to do that, verify the server’s response by issuing requests using different methods. This can be achieved by manual testing or something like the
http-methods Nmap script.
To use the
http-methods Nmap script to test the endpoint
/index.php on the server
localhost using HTTPS, issue the command:
nmap -p 443 --script http-methods --script-args http-methods.url-path='/index.php' localhost
When testing an application that has to accept other methods, e.g. a RESTful Web Service, test it thoroughly to make sure that all endpoints accept only the methods that they require.
Testing the PUT Method
- Capture the base request of the target with a web proxy.
Change the request method to
test.htmlfile and send the request to the application server.
PUT /test.html HTTP/1.1 Host: testing-website <html> HTTP PUT Method is Enabled </html>
- If the server response with 2XX success codes or 3XX redirections and then confirm by
test.htmlfile. The application is vulnerable.
If the HTTP
PUT method is not allowed on base URL or request, try other paths in the system.
NOTE: If you are successful in uploading a web shell you should overwrite it or ensure that the security team of the target are aware and remove the component promptly after your proof-of-concept.
PUT method an attacker may be able to place arbitrary and potentially malicious content, into the system which may lead to remote code execution, defacing the site or denial of service.
Testing for Access Control Bypass
Find a page to visit that has a security constraint such that a GET request would normally force a 302 redirect to a log in page or force a log in directly. Issue requests using various methods such as HEAD, POST, PUT etc. as well as arbitrarily made up methods such as BILBAO, FOOBAR, CATS, etc. If the web application responds with a
HTTP/1.1 200 OK that is not a log in page, it may be possible to bypass authentication or authorization. The following example uses Nmap’s
$ ncat www.example.com 80 HEAD /admin HTTP/1.1 Host: www.example.com HTTP/1.1 200 OK Date: Mon, 18 Aug 2008 22:44:11 GMT Server: Apache Set-Cookie: PHPSESSID=pKi...; path=/; HttpOnly Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: adminOnlyCookie1=...; expires=Tue, 18-Aug-2009 22:44:31 GMT; domain=www.example.com Set-Cookie: adminOnlyCookie2=...; expires=Mon, 18-Aug-2008 22:54:31 GMT; domain=www.example.com Set-Cookie: adminOnlyCookie3=...; expires=Sun, 19-Aug-2007 22:44:30 GMT; domain=www.example.com Content-Language: EN Connection: close Content-Type: text/html; charset=ISO-8859-1
If the system appears vulnerable, issue CSRF-like attacks such as the following to exploit the issue more fully:
Using the above three commands, modified to suit the application under test and testing requirements, a new user would be created, a password assigned, and the user made an administrator, all using blind request submission.
Testing for Cross-Site Tracing Potential
Note: in order to understand the logic and the goals of a cross-site tracing (XST) attack, one must be familiar with cross-site scripting attacks.
Test for cross-site tracing potential by issuing a request such as the following:
$ ncat www.victim.com 80 TRACE / HTTP/1.1 Host: www.victim.com Random: Header HTTP/1.1 200 OK Random: Header ...
The web server returned a 200 and reflected the random header that was set in place. To further exploit this issue:
$ ncat www.victim.com 80 TRACE / HTTP/1.1 Host: www.victim.com Attack: <script>prompt()</script>
The above example works if the response is being reflected in the HTML context.
In older browsers, attacks were pulled using XHR technology, which leaked the headers when the server reflects them (e.g. Cookies, Authorization tokens, etc.) and bypassed security measures such as the HttpOnly attribute. This attack can be pulled in recent browsers only if the application integrates with technologies similar to Flash.
Testing for HTTP Method Overriding
Some web frameworks provide a way to override the actual HTTP method in the request by emulating the missing HTTP verbs passing some custom header in the requests. The main purpose of this is to circumvent some middleware (e.g. proxy, firewall) limitation where methods allowed usually do not encompass verbs such as
DELETE. The following alternative headers could be used to do such verb tunneling:
In order to test this, in the scenarios where restricted verbs such as PUT or DELETE return a “405 Method not allowed”, replay the same request with the addition of the alternative headers for HTTP method overriding, and observe how the system responds. The application should respond with a different status code (e.g. 200) in cases where method overriding is supported.
The web server in the following example does not allow the
DELETE method and blocks it:
$ ncat www.example.com 80 DELETE /resource.html HTTP/1.1 Host: www.example.com HTTP/1.1 405 Method Not Allowed Date: Sat, 04 Apr 2020 18:26:53 GMT Server: Apache Allow: GET,HEAD,POST,OPTIONS Content-Length: 320 Content-Type: text/html; charset=iso-8859-1 Vary: Accept-Encoding
After adding the
X-HTTP-Header, the server responds to the request with a 200:
$ ncat www.example.com 80 DELETE /resource.html HTTP/1.1 Host: www.example.com X-HTTP-Method: DELETE HTTP/1.1 200 OK Date: Sat, 04 Apr 2020 19:26:01 GMT Server: Apache
- Ensure that only the required headers are allowed, and that the allowed headers are properly configured.
- Ensure that no workarounds are implemented to bypass security measures implemented by user-agents, frameworks, or web servers.