Parameter Manipulation ?
Manipulating the data sent between the browser and the web application to an attacker's advantage has long been a simple but effective way to make applications do things in a way the user often shouldn't be able to. In a badly designed and developed web application, malicious users can modify things like prices in web carts, session tokens or values stored in cookies and even HTTP headers.No data sent to the browser can be relied upon to stay the same unless cryptographically protected at the application layer. Cryptographic protection in the transport layer (SSL) in no way protects one from attacks like parameter manipulation in which data is mangled before it hits the wire. Parameter tampering can often be done with:
- Cookies
- Form Fields
- URL Query Strings
- HTTP Headers
Cookie Manipulation ?
Description
The extent of cookie manipulation depends on what the cookie is used for but usually ranges from session tokens to arrays that make authorization decisions. (Many cookies are Base64 encoded; this is an encoding scheme and offers no cryptographic protection).
Example from a real world example on a travel web site modified to protect the innocent (or stupid).
Cookie: lang=en-us; ADMIN=no; y=1 ; time=10:30GMT ;
The attacker can simply modify the cookie to; Cookie: lang=en-us; ADMIN=yes; y=1 ; time=12:30GMT ;
Mitigation Techniques ?
Another technique involves building intrusion detection hooks to evaluate the cookie for any infeasible or impossible combinations of values that would indicate tampering. For instance, if the "administrator" flag is set in a cookie, but the userid value does not belong to someone on the development team.
The final method is to encrypt the cookie to prevent tampering. There are several ways to do this including hashing the cookie and comparing hashes when it is returned or a symmetric encryption , although server compromise will invalidate this approach and so response to penetration must include new key generation under this scheme.
HTTP Header Manipulation ?
Description
Host: www.someplace.org
Pragma: no-cache
Cache-Control: no-cache
User-Agent: Lynx/2.8.4dev.9 libwww-FM/2.14
Referer: http://www.someplace.org/login.php
Content-type: application/x-www-form-urlencoded
Content-length: 49
Often HTTP headers are used by the browser and the web server software only. Most web applications pay no attention to them. However some web developers choose to inspect incoming headers, and in those cases it is important to realize that request headers originate at the client side, and they may thus be altered by an attacker.Normal web browsers do not allow header modification. An attacker will have to write his own program (about 15 lines of perl code will do) to perform the HTTP request, or he may use one of several freely available proxies that allow easy modification of any data sent from the browser.
Example 1: The Referer header (note the spelling), which is sent by most browsers, normally contains the URL of the web page from which the request originated. Some web sites choose to check this header in order to make sure the request originated from a page generated by them, for example in the belief it prevents attackers from saving web pages, modifying forms, and posting them off their own computer. This security mechanism will fail, as the attacker will be able to modify the Referer header to look like it came from the original site.
Example 2: The Accept-Language header indicates the preferred language(s) of the user. A web application doing internationalization (i18n) may pick up the language label from the HTTP header and pass it to a database in order to look up a text. If the content of the header is sent verbatim to the database, an attacker may be able to inject SQL commands (see SQL injection) by modifying the header. Likewise, if the header content is used to build a name of a file from which to look up the correct language text, an attacker may be able to launch a path traversal attack.
Mitigation Techniques ?
Further Reading
HTML Form Field Manipulation ?
Description
Whether these form fields are pre-selected (drop down, check boxes etc.), free form or hidden, they can all be manipulated by the user to submit whatever values he/she chooses. In most cases this is as simple as saving the page using "view source", "save", editing the HTML and re-loading the page in the web browser.
As an example an application uses a simple form to submit a username and password to a CGI for authentication using HTTP over SSL. The username and password form fields look like this.
Some developers try to prevent the user from entering long usernames and passwords by setting a form field value maxlength=(an integer) in the belief they will prevent the malicious user attempting to inject buffer overflows of overly long parameters. However the malicious user can simply save the page, remove the maxlength tag and reload the page in his browser. Other interesting form fields include disabled, readonly and value. As discussed earlier, data (and code) sent to clients must not be relied upon until in responses until it is vetted for sanity and correctness. Code sent to browsers is merely a set of suggestions and has no security value.
Hidden Form Fields represent a convenient way for developers to store data in the browser and are one of the most common ways of carrying data between pages in wizard type applications. All of the same rules apply to hidden forms fields as apply to regular form fields.
Example 2 - Take the same application. Behind the login form may have been the HTML tag;
<input name="masteraccess" type="hidden" value="N">
By manipulating the hidden value to a Y, the application would have logged the user in as an Administrator. Hidden form fields are extensively used in a variety of ways and while it's easy to understand the dangers they still are found to be significantly vulnerable in the wild.Mitigation Techniques ?
If the above technique of using a session variable instead of a hidden field cannot be implemented, a second approach is as follows.
The name/value pairs of the hidden fields in a form can be concatenated together into a single string. A secret key that never appears in the form is also appended to the string. This string is called the Outgoing Form Message. An MD5 digest or other one-way hash is generated for the Outgoing Form Message. This is called the Outgoing Form Digest and it is added to the form as an additional hidden field.
When the form is submitted, the incoming name/value pairs are again concatenated along with the secret key into an Incoming Form Message. An MD5 digest of the Incoming Form Message is computed. Then the Incoming Form Digest is compared to the Outgoing Form Digest (which is submitted along with the form) and if they do not match, then a hidden field has been altered. Note, for the digests to match, the name/value pairs in the Incoming and Outgoing Form Messages must concatenated together in the exact same order both times.
This same technique can be used to prevent tampering with parameters in a URL. An additional digest parameter can be added to the URL query string following the same technique described above.
URL Manipulation ?
Description
HTML Forms may submit their results using one of two methods: GET or POST. If the method is GET, all form element names and their values will appear in the query string of the next URL the user sees. Tampering with hidden form fields is easy enough, but tampering with query strings is even easier. One need only look at the URL in the browser's address bar.
Take the following example; a web page allows the authenticated user to select one of his pre-populated accounts from a drop-down box and debit the account with a fixed unit amount. It's a common scenario. His/her choices are recorded by pressing the submit button. The page is actually storing the entries in form field values and submitting them using a form submit command. The command sends the following HTTP request.
http://www.victim.com/example?accountnumber=12345&debitamount=1
A malicious user could construct his own account number and change the parameters as follows:http://www.victim.com/example?accountnumber=67891&creditamount=999999999
Thee new parameters would be sent to the application and be processed accordingly.
This seems remarkably obvious but has been the problem behind several well-published attacks including one where hackers bought tickets from the US to Paris for $25 and flew to hold a hacking convention. Another well-known electronic invitation service allowed users to guess the account ID and login as a specific user this way; a fun game for the terminally bored with voyeuristic tendencies.
Unfortunately, it isn't just HTML forms that present these problems. Almost all navigation done on the internet is through hyperlinks. When a user clicks on a hyperlink to navigate from one site to another, or within a single application, he is sending GET requests. Many of these requests will have a query string with parameters just like a form. And once again, a user can simply look in the "Address" window of his browser and change the parameter values.
Mitigation Techniques ?
When parameters need to be sent from a client to a server, they should be accompanied by a valid session token. The session token may also be a parameter, or a cookie. Session tokens have their own special security considerations described previously. In the example above, the application should not make changes to the account without first checking if the user associated with the session has permission to edit the account specified by the parameter "accountnumber". The script that processes a credit to an account cannot assume that access control decisions were made on previous application pages. Parameters should never be operated on unless the application can independently validate they were bound for and are authorized to be acted on.
However, a second form of tampering is also evident in the example. Notice that the creditamount is increased from 1 to 999999999. Imagine that the user doesn't tamper with the accountnumber but only with the amount. He may be crediting his own account with a very large sum instead of $1. Clearly this is a parameter that should simply not be present in the URL.
There are two reasons why a parameter should not be a URL (or in a form as a hidden field). The above example illustrates one reason - the parameter is one the user should not be able to set the value of. The second is if a parameter is one the user should not be able to see the value of. Passwords are a good example of the latter. Users's should not even see their own passwords in a URL because someone may be standing behind them and because browsers record URL histories. See Browser History Attack.
If a sensitive parameter cannot be removed from a URL, it must be cryptographically protected. Cryptographic protection can be implemented in one of two ways. The better method is to encrypt an entire query string (or all hidden form field values). This technique both prevents a user from setting the value and from seeing the value.
A second form of cryptographic protection is to add an additional parameter whose value is an MD5 digest of the URL query string (or hidden form fields) More details of this technique are described above in the section "HTML Form Field Manipulation". This method does not prevent a user from seeing a value, but it does prevent him from changing the value.
Miscellaneous ?
Vendors Patches
A significant part of the web application is typically not customized and specific for a single web site but rather made up of standard products supplied by 3rd party vendors. Typically such products serve as the web server, application server, databases and more specific packages used in the different vertical markets. All such products have vulnerabilities that are discovered in an ongoing manner and in most cases disclosed directly to the vendor (although there are also cases in which the vulnerability is revealed to the public without disclosure to the vendor). The vendor will typically address the vulnerability by issuing a patch and making it available to the customers using the product, with or without revealing the full vulnerability. The patches are sometimes grouped in patch groups (or updates) that may be released periodically.
A vendors disclosure policy of vulnerabilities is of primary concern to those deploying ciritcal systems. Those in a procurement position should be very aware of the End User License Agreements (EULAs) under which vendors license their software. Very often these EULAs disclaim all liability on the part of the vendor, even in cases of serious neglect, leaving users with little or no recourse. Those deploying software distributed under these licenses are now fully liable for damage caused by the defects that may be a part of this code. Due to this state of affairs, it becomes ever more important that orginizations insist upon open discussion and disclosure of vulnerabilities in the software they deploy. Vendors have reputations at stake when new vulnerabilities are disclosed and many attempt to keep such problems quiet, thereby leaving their clients without adequate information in asessing their exposure to threats. This behaviour is unacceptable in a mature software industry and should not be tollerated. Furthermore, orginizations should take care to ensure that vendors do not attempt to squelch information needed to verify the validity and effectiveness of patches. While this might seem a frivilous concern at first glance, vendors have been known to try to limit distribution of this information in order to provide "security" through obscurity. Customers may be actively harmed in the meanwhile as Black Hats have more information about a problem than White Hats do, again imparing an organizations ability to assess its risk exposure.
The main issue with vendor patches is the latency between the disclosure of the vulnerability to the actual deployment of the patch in the production environment i.e. the patch latency and the total time needed to issue the patch by the vendor, download of the patch by the client, test of the patch in a QA or staging environment and finally full deployment in the production site. During all this time the site is vulnerable to attacks on this published vulnerability. This results in misuse of the patch releases to achieve opposite results by humans and more recently by worms such as CodeRed.
Most patches are released by the vendors only in their site and in many cases published only in internal mailing lists or sites. Sites and lists following such vulnerabilities and patches (such as bugtraq) do not serve as a central repository for all patches. The number of such patches for mainstream products is estimated at dozens a month.
The final critical aspect of patches is that they are not (in most cases) signed or containing a checksum causing them to be a potential source of Trojans in the system.
You should subscribe to vendors' security intelligence service for all software that forms part of your web application or a security infrastructure.
System Configuration
Server software is often complex, requiring much understanding of both the protocols involved and their internal workings to correctly configure. Unfortunantly software makes this task much more difficult by providing default configurations which are known to be vulnerable to devastating attacks. Often "sample" files and directories are installed by default which may provide attackers with ready-made attacks should problems be found in the sample files. While many vendors suggest removing these files by default, they put the onus of securing an "out of the box" installation on those deploying their product. A (very) few vendors attempt to provide secure defaults for their systems (the OpenBSD project being an example). Systems from these vendors often prove much less vulnerable to widespread attack, this approach to securing infrastructure appears to work very well and should be encouraged when discussing procurement with vendors.
If a vendor provides tools for managing and securing installations for your software, it may be worth evaluating these tools, however they will never be a full replacement for understanding how a system is designed to work and strictly managing configurations across your deployed base.
Understanding how system configuration affects security is crucial to effective risk management. Systems being deploying today rely on so many layers of software that a system may be compromised from vectors which may be difficult or impossible to predict. Risk management and threat analysis seeks to quantify this risk, minimize the impact of the inevitable failure, and provide means (other than technical) for compensating for threat exposure. Configuration management is a well understood piece of this puzzle, yet remains maddeningly difficult to implement well. As configurations and environmental factors may change over time, a system once well shielded by structural safeguards may become a weak link with very little outward indication that the risk inherent in a system has changed. Organizations will have to accept that configuration management is a continuing process and cannot simply be done once and let be. Effectively managing configurations can be a first step in putting in place the safeguards that allow systems to perform reliably in the face of concerted attack.
Comments in HTML ?
Description
Comments left in HTML can come in many formats, some as simple as directory structures, others inform the potential attacker about the true location of the web root. Comments are sometimes left in from the HTML development stage and can contain debug information, cookie structures, problems associated with development and even developer names, emails and phone numbers.
Structured Comments - these appear in HTML source, usually at the top of the page or between the JavaScript and the remaining HTML, when a large development team has been working on the site for some time.
Automated Comments - many widely used page generation utilities and web usage software automatically adds signature comments into the HTML page. These will inform the attacker about the precise software packages (sometimes even down to the actual release) that is being used on the site. Known vulnerabilities in those packages can then be tried out against the site.
Unstructured Comments - these are one off comments made by programmers almost as an "aid memoir" during development. These can be particularly dangerous as they are not controlled in any way. Comments such as "The following hidden field must be set to 1 or XYZ.asp breaks" or "Don't change the order of these table fields" are a red flag to a potential attacker and sadly not uncommon.
Mitigation Techniques ?
Old, Backup and Un-referenced Files ?
Description
File /Application enumeration uses the HTTP server response codes to determine if a file or application exists. A web server will typically return an HTTP 200 response code if the file exists and an HTTP 404 response code if the file does not exist. This enables an attacker to feed in lists of known vulnerable files and suspected applications or use some basic logic to map the file and application structure visible from the presentation layer.
Known Vulnerable Files - Obviously many known vulnerable files exist, and in fact looking for them is one of the most common techniques that commercial and free-ware vulnerability scanners use. Many people will focus their search on cgi's for example or server specific issues such as IIS problems. Many daemons install "sample" code in publicly accessible locations, which are often found to have security problems. Removing (or simply not installing) such default files cannot be recommended highly enough.
Hidden / Un-Referenced Files - Many web site administrators leave files on the web server such as sample files or default installation files. When the web content is published, these files remain accessible although are un-referenced by any HTML in the web. Many examples are notoriously insecure, demonstrating things like uploading files from a web interface for instance. If an attacker can guess the URL, then he is typically able to access the resource.
Back-Up Files / Temp Files - Many applications used to build HTML and things like ASP pages leave temp files and back-up files in directories. These often get up-loaded either manually in directory copies or automagically by site management modules of HTML authoring tools like Microsoft's Frontpage or Adobe Go-Live. Back-up files are also dangerous as many developers embed things into development HTML that they later remove for production. Emacs for instance writes a *.bak in many instances. Development staff turnover may also be an issue, and security through obscurity is always an ill-advised course of action.
Mitigation Techniques ?
Some web server / application servers that build dynamic pages will not return a 404 message to the browser, but instead return a page such as the site map. This confuses basic scanners into thinking that all files exist. Modern vulnerability scanners however can take a custom 404 and treat it as a vanilla 404 so this technique only slows progress.
Debug Commands ?
Description
Explicit Commands - this is where a name value pair has been left in the code or can be introduced as part of the URL to induce the server to enter debug mode. Such commands as "debug=on" or
"Debug=YES" can be placed on the URL like:
http://www.somewebsite.com/account_check?ID=8327dsddi8qjgqllkjdlas&Disp=no
Can be altered to:http://www.somewebsite.com/account_check?debug=on&ID=8327dsddi8qjgqllkjdlas&Disp=no
The attacker observes the resultant server behavior. The debug construct can also be placed inside HTML code or JavaScript when a form is returned to the server, simply by adding another line element to the form construction, the result is the same as the command line attack above.Implicit Commands - this is where seemingly innocuous elements on a page if altered have dramatic effects on the server. The original intent of these elements was to help the programmer modify the system into various states to allow a faster testing cycle time. These element are normally given obscure names such as "fubar1" or "mycheck" etc. These elements may appear in the source as:
<!-- begins -->
<TABLE BORDER=0 ALIGN=CENTER CELLPADDING=1 CELLSPACING=0>>
<FORM METHOD=POST ACTION="http://some_poll.com/poll?1688591" TARGET="sometarget" FUBAR1="666">
<INPUT TYPE=HIDDEN NAME="Poll" VALUE="1122">
<!-- Question 1 -->
<TR>
<TD align=left colspan=2>
<INPUT TYPE=HIDDEN NAME="Question" VALUE="1">
<SPAN class="Story">
Finding debug elements is not easy, but once one is located it is usually tried across the entire web site by the potential hacker. As designers never intend for these commands to be used by normal users, the precautions preventing parameter tampering are usually not taken.Debug commands have been known to remain in 3rd party code designed to operate the web site, such as web servers, database programs. Search the web for "Netscape Engineers are weenies" if you don't believe us!
Default Accounts ?
Description
Web applications enable multiple default accounts on the system, for example:
- Administrator accounts
- Test accounts
- Guest accounts
The attack on such default accounts can occur in two ways:
- Attempt to use the default username/password assuming that it was not changed during the default installation.
- Enumeration over the password only since the user name of the account is known.
If the account was an administrator account then the attacker has partial or complete control over the application (and sometimes, the whole site) with the ability to perform any malicious action.
If the account was a demo or test account the attacker will use this account as a means of accessing and abusing the application logic exposed to that user and using it as a mean of progressing with the attack.
Mitigation Techniques ?
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as usually this post is for completely educational purpose and I did not take any responsibility of any misuse, Hacking email accounts is criminal activity and is punishable under cyber crime and you may get upto 40 years of imprisonment, if got caught in doing so. you will be solely responsible for any misuse that you do.
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