It's a common and sensible practice to install records of the form "localhost. IN A The missing dot indicates that the record is not fully qualified, and thus queries of the form "localhost.
While superficially this may appear to be harmless, it does in fact allow an attacker to cheat the RFC HTTP State Management Mechanism same origin restrictions, and therefore hijack state management data. The result of this minor misconfiguration is that it is impossible to access sites in affected domains securely from multi-user systems.
The attack is trivial, for example, from a shared UNIX system, an attacker listens on an unprivileged port and then uses a typical XSS attack vector e. The request will include the RFC Cookie header, which could then be used to steal credentials or interact with the affected service as if they were the victim. Another attack vector exists where a victim connects to a site from or via a machine that hosts another website, any XSS-like flaw or reflective web service on the hosted website can therefore be exploited in the context of the misconfigured domain.
This would also affect users who connect via a shared caching http proxy machine, that also hosts an http daemon. The bug requires a click to be exploited, but illustrates the problem nicely. Initial analysis shows that some of the worlds most popular websites are affected.
The administrators of the example domains listed below were sent a draft of this email 7 days before release, so some or all may have been corrected, these examples are simply intended to demonstrate how widespread this problem is. Recommendations It is advised that non-FQ localhost entries be removed from nameserver configurations for domains that host websites that rely on HTTP state management. Of course, any other records that return RFC or RFC reserved addresses should also be carefully examined for similar issues.
Additionally, those practising blackhole routing via dns to mitigate denial of service attacks against specific hostnames should avoid the temptation to resolve targets to This behaviour is arguably incorrect, making it impossible to securely host a website from a multi-user machine, but nevertheless is the case, and is implemented by most major browsers.In this section, we'll explain what cross-site scripting is, describe the different varieties of cross-site scripting vulnerabilities, and spell out how to find and prevent cross-site scripting.
Cross-site scripting also known as XSS is a web security vulnerability that allows an attacker to compromise the interactions that users have with a vulnerable application.Website Hacking - What is Cross Site Scripting (XSS)?
It allows an attacker to circumvent the same origin policy, which is designed to segregate different websites from each other. Cross-site scripting vulnerabilities normally allow an attacker to masquerade as a victim user, to carry out any actions that the user is able to perform, and to access any of the user's data. If the victim user has privileged access within the application, then the attacker might be able to gain full control over all of the application's functionality and data.
Here is a simple example of a reflected XSS vulnerability:. The application doesn't perform any other processing of the data, so an attacker can easily construct an attack like this:. If the user visits the URL constructed by the attacker, then the attacker's script executes in the user's browser, in the context of that user's session with the application. At that point, the script can carry out any action, and retrieve any data, to which the user has access. Stored XSS also known as persistent or second-order XSS arises when an application receives data from an untrusted source and includes that data within its later HTTP responses in an unsafe way.
The data in question might be submitted to the application via HTTP requests; for example, comments on a blog post, user nicknames in a chat room, or contact details on a customer order. In other cases, the data might arrive from other untrusted sources; for example, a webmail application displaying messages received over SMTP, a marketing application displaying social media posts, or a network monitoring application displaying packet data from network traffic. Here is a simple example of a stored XSS vulnerability.
The actual impact of an XSS attack generally depends on the nature of the application, its functionality and data, and the status of the compromised user. For example:. The vast majority of XSS vulnerabilities can be found quickly and reliably using Burp Suite's web vulnerability scanner.
This article provides insight into how to test your applications for Cross-Site Scripting XSS defects using both manual and automated means. While a survey of these are beyond the scope of this article, a word of caution is in order. The use of automated tools can lend a false sense of security to developers and testers, since the tools can be blind to certain variations of Cross-Site Scripting XSS defects.
It may turn out that with a little syntax tweaking, it is exploitable. It may turn out that it is not. Despite having some limitations, automated tools are indispensable when searching for Cross-Site Scripting XSS vulnerabilities.
Manual testing should augment automated testing for the reasons cited above. Of course the key to successful manual discovery is to understand exactly how reflected inputs appear in the response, and how to potentially exploit that specific situation.
Some trial and error is typically required. This combined approach also allows you to rapidly identify anomalous responses that may be indicative of a potentially successful exploit.
It is important that you do not overlook potential sources of untrusted input, as doing so may mean you overlook a potential problem. Keep in mind that:. We hope you found this article to be useful.
In fact, we train developers and IT staff how to hack applications and networks. Perhaps it was a network scan or website vulnerability test that brought you here.
If so, you are likely researching how to find, fix, or avoid a particular vulnerability. We urge you to be proactive and ensure that key individuals in your organization understand not only this issue, but also are more broadly aware of application security. Although every effort has been made to provide the most useful and highest quality information, it is unfortunate but inevitable that some errors, omissions, and typographical mistakes will appear in these articles.
Consequently, Affinity IT Security will not be responsible for any loss or damages resulting directly or indirectly from any error, misunderstanding, software defect, example, or misuse of any content herein. Maintain compliance.
Retain control. Find Out How. Sources of Untrusted Input It is important that you do not overlook potential sources of untrusted input, as doing so may mean you overlook a potential problem. Find and Fix Your Vulnerabilities.Cross-site Scripting XSS is a client-side code injection attack. The attacker aims to execute malicious scripts in a web browser of the victim by including malicious code in a legitimate web page or web application.
The actual attack occurs when the victim visits the web page or web application that executes the malicious code.
The attacker can use injected scripts to change the content of the website or even redirect the browser to another web page, for example, one that contains malicious code.
XSS vulnerabilities provide the perfect ground to escalate attacks to more serious ones. You can read more about them in an article titled Types of XSS. For step one to be possible, the vulnerable website needs to directly include user input in its pages.
There are also variants of XSS attacks where the attacker lures the user to visit a URL using social engineering and the payload is part of the link that the user clicks. The following is a snippet of server-side pseudocode that is used to display the most recent comment on a web page:. The above script simply takes the latest comment from a database and includes it in an HTML page.
It assumes that the comment printed out consists of only text and contains no HTML tags or other code. It is vulnerable to XSS, because an attacker could submit a comment that contains a malicious payload, for example:. Most often, the victim does not realize it and is unable to prevent such an attack. Criminals often use XSS to steal cookies. This allows them to impersonate the victim. The attacker can send the cookie to their own server in many ways. To learn more about how XSS attacks are conducted, you can refer to an article titled A comprehensive tutorial on cross-site scripting.
The following is a list of common XSS attack vectors that an attacker could use to compromise the security of a website or web application through an XSS attack.
When a request is sent from a browser to a website, the browser checks if it has a stored cookie that belongs to that website. While carrying out this process, it checks to see whether the properties and flags of the cookies domain, path, securematch the website's data which has been requested.
If they match, the browser sends the relevant cookies along with the request. This behavior is also repeated in the same way for requests made by third parties through the browser.
By "third parties" we mean other websites that we don't visit directly. The critical point from a web application security perspective is that when you visit website A, all cookies kept in the browser for site B will be added to the request initiated toward site B by site A. So, a session that belongs to B on the browser can be used and even abused in this way. It is carried out by misusing a session belonging to an authorized user by using this browser behavior.
This browser behavior can also be misused for other purposes like tracking users or advertising. When you enter a site, for instance example. Along with these requests, the cookies in the browser that belong to these other sites will also be sent.
Therefore those third parties can track and log your activity by using Cookie and Referrer information. Normally, it is possible to avoid tracking like this in Firefox and Chrome browsers. However, when these browsers block tracking, they prevent the sending of cookies along with the request made by any third party website. But by doing so your browsing experience will be very poor.
So by blocking cookies, you can totally prevent CSRF, but is it worth the consequences?
Cross-site Scripting (XSS)
Thanks to a new cookie attribute, that Google Chrome started supporting on the 29th of Marchand other the popular browsers followed, there is now a solution. It is called the Same-Site cookie attribute. Developers can now instruct browsers to control whether cookies are sent along with the request initiated by third party websites - by using the SameSite cookie attribute, which is a more practical solution than denying the sending of cookies.
Setting a Same-Site attribute to a cookie is quite simple. It consists of adding just one instruction to the cookie. Strict : As the name suggests, this is the option in which the Same-Site rule is applied strictly. When the SameSite attribute is set as Strict, the cookie will not be sent along with requests initiated by third party websites.
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I know it is an issue with how DNS is configuredbut is it really dangerous if the attacker couldn't access your network? Based on the link from Julian's answer, it's pretty straightforward. It does seem a little dangerous but nothing critical. Imagine you have a website. Browsers send HTTP traffic to that website. This traffic includes session cookies. The site should be TLS protected, or your session cookies are going over the internet in cleartext, for anyone to read. You also need to protect your session cookies and any other sensitive cookies with the 'secure' flag to prevent them from being sent over http traffic, or your browser will just send them to any server that intercepts your cleartext http requests.
And you can use HSTS to prevent usage of http to your server. When the browser tries to communicate with the web server, it communicates via IP -internet protocol. Internet protocol doesn't use host names, but rather uses ip addresses - 4 decimal separated values such as The web server has an associated dns server whose job it is to respond to 'what ip address is this host'.
Every named host on the internet is supported by a dns server. But what happens if the dns server is misconfigured and returns the wrong ip address? If the desired server is www. The browser connects to 6. Now, this isn't so bad at first blush.
Remember how the traffic is TLS protected? Well, TLS lets the browser detect that 6. The browser rejects the connection attempt to evil. Ah, but what if TLS isn't used to connect to 6. In that case, there is a risk. The cookies don't get sent, because you remembered to use the secure flag on your cookies. However, the same domain policy that protects pages served from one domain against pages served from another domain breaks down - these servers are both in the same domain.
How To Test For Cross-Site Scripting (XSS)
The DNS server owned by example. Typos causing this are unlikely. Even if a typo did occur, users would notice outages before the attacker would likely have the time to make use of the window of opportunity.Cross-site scripting XSS is a type of computer security vulnerability typically found in web applications.
XSS attacks enable attackers to inject client-side scripts into web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls such as the same-origin policy. Security on the web depends on a variety of mechanisms, including an underlying concept of trust known as the same-origin policy.
Content from URLs where any of these three attributes are different will have to be granted permissions separately. Cross-site scripting attacks use known vulnerabilities in web-based applications, their servers, or the plug-in systems on which they rely.
Exploiting one of these, attackers fold malicious content into the content being delivered from the compromised site. When the resulting combined content arrives at the client-side web browser, it has all been delivered from the trusted source, and thus operates under the permissions granted to that system. By finding ways of injecting malicious scripts into web pages, an attacker can gain elevated access-privileges to sensitive page content, to session cookies, and to a variety of other information maintained by the browser on behalf of the user.
XSS vulnerabilities have been reported and exploited since the s. There is no single, standardized classification of cross-site scripting flaws, but most experts distinguish between at least two primary flavors of XSS flaws: non-persistent and persistent.
Some sources further divide these two groups into traditional caused by server-side code flaws and DOM -based in client-side code. The non-persistent or reflected cross-site scripting vulnerability is by far the most basic type of web vulnerability. HTML form submissionis used immediately by server-side scripts to parse and display a page of results for and to that user, without properly sanitizing the content. Because HTML documents have a flat, serial structure that mixes control statements, formatting, and the actual content, any non-validated user-supplied data included in the resulting page without proper HTML encoding, may lead to markup injection.
If this response does not properly escape or reject HTML control characters, a cross-site scripting flaw will ensue. A reflected attack is typically delivered via email or a neutral web site. If the trusted site is vulnerable to the vector, clicking the link can cause the victim's browser to execute the injected script.
The persistent or stored XSS vulnerability is a more devastating variant of a cross-site scripting flaw: it occurs when the data provided by the attacker is saved by the server, and then permanently displayed on "normal" pages returned to other users in the course of regular browsing, without proper HTML escaping. A classic example of this is with online message boards where users are allowed to post HTML formatted messages for other users to read.
For example, suppose there is a dating website where members scan the profiles of other members to see if they look interesting. For privacy reasons, this site hides everybody's real name and email. These are kept secret on the server. The only time a member's real name and email are in the browser is when the member is signed inand they can't see anyone else's. Suppose that Mallory, an attacker, joins the site and wants to figure out the real names of the people she sees on the site.
To do so, she writes a script designed to run from other users' browsers when they visit her profile. The script then sends a quick message to her own server, which collects this information. To do this, for the question "Describe your Ideal First Date", Mallory gives a short answer to appear normal but the text at the end of her answer is her script to steal names and emails.
Then suppose that Bob, a member of the dating site, reaches Mallory's profile, which has her answer to the First Date question. Her script is run automatically by the browser and steals a copy of Bob's real name and email directly from his own machine.