Stored and Reflected XSS Attacks
- Stored XSS Attacks. Stored attacks are those where the injected script is permanently stored on the target servers, such as in a database, in a message forum, visitor log, comment ...
- Blind Cross-site Scripting. Blind Cross-site Scripting is a form of persistent XSS. ...
- Reflected XSS Attacks. ...
What do you need to know about XSS attack?
Types of XSS Attacks
- Stored cross-site scripting. A stored XSS vulnerability (a.k.a. Persistent or Type I) takes place when user input is stored in a database, comment field, visitor log, or other target servers.
- Reflected cross-site scripting. A reflected XSS vulnerability (a.k.a. ...
- DOM-based XSS. TA DOM-based XSS vulnerability (a.k.a. ...
Do XSS attacks work on mobile phones?
Do XSS attacks work on mobile phones? “XSS attacks can only target at web applications through a single channel (Internet) but with the adoption of the same technology in mobile devices, we have found out that a similar type of attack can not only be launched against mobile apps,” Gartner noted.
How is this XSS attack working?
This attack is divided into three main categories as shown below:
- Reflected XSS – This attack occurs, when a malicious script is not being saved on the web server but reflected in the website’s results.
- Stored XSS – This attack occurs when a malicious script is being saved on the web server permanently.
- DOM – This occurs, when the DOM environment is being changed, but the code remains the same.
How to fix XSS vulnerability?
Mitigations:
- Try to use browser technologies that do not allow client-side scripting in input fields or URLs.
- Use strict type character and encoding enforcement to avoid XSS.
- Make sure that all the user-supplied inputs are adequately validated before sending them to the server.
What is XSS attack with example?
Examples of reflected cross-site scripting attacks include when an attacker stores malicious script in the data sent from a website's search or contact form. A typical example of reflected cross-site scripting is a search form, where visitors sends their search query to the server, and only they see the result.
Why is stored XSS bad?
XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. The most severe XSS attacks involve disclosure of the user's session cookie, allowing an attacker to hijack the user's session and take over the account.
Where is XSS stored?
Stored XSS generally occurs when user input is stored on the target server, such as in a database, in a message forum, visitor log, comment field, etc. And then a victim is able to retrieve the stored data from the web application without that data being made safe to render in the browser.
What are the three types of XSS attacks?
Cross-site Scripting can be classified into three major categories — Stored XSS, Reflected XSS, and DOM-based XSS.
What can you do with a stored XSS?
By stealing session cookies, a hacker can perform session hijacking, allowing them to impersonate their victim within the site and potentially gain access to all kinds of private information. Persistent XSS attacks can also be used to alter the appearance of a website, like a kind of digital graffiti.
What's the difference between stored and reflected XSS?
Stored XSS, also known as persistent XSS, is the more damaging of the two. It occurs when a malicious script is injected directly into a vulnerable web application. Reflected XSS involves the reflecting of a malicious script off of a web application, onto a user's browser.
Is stored XSS client or server side?
XSS is a client-side vulnerability that targets other application users, while SQL injection is a server-side vulnerability that targets the application's database.
How are stored XSS payloads usually stored on a website?
Typical Entry Points for Stored XSS Stored XSS requires user supplied input to be stored by the application (making it persistent) and rendered within the page.
What are two types of cross site attacks?
XSS attacks can be generally categorized into two main types: non-persistent (reflected) and persistent (stored). The less common type called DOM Based XSS attack will not be covered in this post.
Why XSS is called cross-site scripting?
Cross-site scripting (XSS) is a type of security vulnerability that can be found in some web applications. XSS attacks enable attackers to inject client-side scripts into web pages viewed by other users.
What is XSS and CSRF?
Cross-site scripting (or XSS) allows an attacker to execute arbitrary JavaScript within the browser of a victim user. Cross-site request forgery (or CSRF) allows an attacker to induce a victim user to perform actions that they do not intend to.
What is XSS and types of XSS?
XSS is an injection attack that exploits the fact that browsers cannot differentiate between valid scripts and attacker-controlled scripts. XSS attacks bypass the same-origin policy, which is designed to prevent scripts that originate in one website from interacting with other scripts from different websites.
How can Stored cross-site scripting be prevented?
In general, effectively preventing XSS vulnerabilities is likely to involve a combination of the following measures: Filter input on arrival. At the point where user input is received, filter as strictly as possible based on what is expected or valid input. Encode data on output.
How are stored XSS payloads usually stored on a website?
Typical Entry Points for Stored XSS Stored XSS requires user supplied input to be stored by the application (making it persistent) and rendered within the page.
What is blind XSS?
Overview of Blind Cross-site Scripting Blind XSS vulnerabilities are a variant of persistent XSS vulnerabilities. They occur when the attacker input is saved by the web server and executed as a malicious script in another part of the application or in another application.
What is persistence XSS?
A persistent cross-site scripting (stored XSS) attack is possible when a website or web application stores user input and later serves it to other users. Attackers use vulnerable web pages to inject malicious code and have it stored on the web server for later use.
Why are persistent XSS attacks harder to execute?
From the perpetrator’s standpoint, persistent XSS attacks are relatively harder to execute because of the difficulties in locating both a trafficked website and one with vulnerabilities that enables permanent script embedding.
What is stored attack?
Unlike a reflected attack, where the script is activated after a link is clicked, a stored attack only requires that the victim visit the compromised web page. This increases the reach of the attack, endangering all visitors no matter their level of vigilance.
What is XSS reflection?
Reflected XSS involves the reflecting of a malicious script off of a web application, onto a user’s browser. The script is embedded into a link, and is only activated once that link is clicked on.
What is cross site scripting?
Cross site scripting (XSS) is a common attack vector that injects malicious code into a vulnerable web application. XSS differs from other web attack vectors (e.g., SQL injections ), in that it does not directly target the application itself. Instead, the users of the web application are the ones at risk.
What are the two types of cross site scripting attacks?
Cross site scripting attacks can be broken down into two types: stored and reflected.
What is the most frequent target of malware?
One of the most frequent targets are websites that allow users to share content, including blogs, social networks, video sharing platforms and message boards. Every time the infected page is viewed, the malicious script is transmitted to the victim’s browser.
Does HTML tag in comment allow to steal cookies?
From this point on, every time the page is accessed, the HTML tag in the comment will activate a JavaScript file, which is hosted on another site, and has the ability to steal visitors’ session cookies.
What is XSS attack?
XSS attacks can generally be categorized into two categories: stored and reflected. There is a third, much less well-known type of XSS attack called DOM Based XSS that is discussed separately here.
What is XSS in web?
Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted websites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it.
What is blind cross site scripting?
Blind Cross-site Scripting is a form of persistent XSS. It generally occurs when the attacker’s payload saved on the server and reflected back to the victim from the backend application. For example in feedback forms, an attacker can submit the malicious payload using the form, and once the backend user/admin of the application will open the attacker’s submitted form via the backend application, the attacker’s payload will get executed. Blind Cross-site Scripting is hard to confirm in the real-world scenario but one of the best tools for this is XSS Hunter.
What is XSS in web browser?
The malicious content sent to the web browser often takes the form of a segment of JavaScript, but may also include HTML, Flash, or any other type of code that the browser may execute. The variety of attacks based on XSS is almost limitless, but they commonly include transmitting private data, like cookies or other session information, to the attacker, redirecting the victim to web content controlled by the attacker, or performing other malicious operations on the user’s machine under the guise of the vulnerable site.
How to find XSS flaws?
The best way to find flaws is to perform a security review of the code and search for all places where input from an HTTP request could possibly make its way into the HTML output.
What is reflected XSS?
When a user is tricked into clicking on a malicious link, submitting a specially crafted form, or even just browsing to a malicious site, the injected code travels to the vulnerable web site, which reflects the attack back to the user’s browser. The browser then executes the code because it came from a “trusted” server. Reflected XSS is also sometimes referred to as Non-Persistent or Type-II XSS.
Where does cross site scripting occur?
Cross-site scripting attacks may occur anywhere that possibly malicious users are allowed to post unregulated material to a trusted website for the consumption of other valid users.
Why do XSS attacks succeed?
Email server consoles. Stored XSS attacks succeed because of the user’s trust in genuine websites – the site just happens to have a vulnerability that can be exploited via XSS.
Why are persistent XSS attacks so significant?
Persistent XSS attacks are therefore such a significant threat because they can have such a wide-ranging reach and do not require a social engineering phase (like Reflected XSS attacks do, which we’ll cover in our next installment of this series) to get users to take a specific action like clicking a link.
How does XSS work?
Stored X SS works in a similar manner. The attack vector ends up being permanently stored (hence the name) on the website’s server, and anyone that accesses the page thus becomes susceptible to the affects of the malicious code that lives there. Persistent XSS attacks are therefore such a significant threat because they can have such ...
What is the most dangerous type of XSS attack?
Stored XSS can end up being the most dangerous type of XSS attack because of the way they’re carried out. Which scenario results in the most overall damage – a) a bad guy targets every single person that visits an ATM via a card scanner that’s planted within the machine, or b) he instead sneaks up behind a single, particular person and watches as he enters their PIN. The former scenario would end up having a broader and more severe effect because the hacking device (the card scanner) is stored on the ATM, and thus every single person that accesses is potentially a victim.
What happens if a hacker is able to include a malicious script when posting a comment on?
For example, if a hacker was able to include a malicious script when posting a comment on a popular blog, every person who read that blog article would be exposed to the malicious script. The attacker’s code is incorrectly treated as valid input by the site in question and doesn’t get properly encoded as a result.
What is persistent cross site scripting?
Persistent cross-site scripting attacks are able to occur when sites or web applications allow user input but don’t properly sanitize or restrict the contents of it. This allows for malicious code to be entered as input, which is then stored on the server and displayed to unsuspecting site visitors.
How to find XSS vulnerability?
Use vulnerability scanners to locate XSS vulnerabilities on your site. These work by testing every single entry point (places where users can input data to be processed by the site) and exit point (places where responses appear).
What is stored XSS?
XSS is a technique of injecting malicious code into a vulnerable web application. Unlike other attacks, the goal however isn’t to run it on your server, but on your users’ browsers! Depending on the attacker’s creativity and skills, this malicious code can steal sensitive information from a user, impersonate a user, or even perform some actions on behalf of the user. A couple of examples of how XSS could be dangerous are as follows:
Where is XSS stored?
In stored XSS, the malicious code is stored on the server of the application. Stored XSS is possible only when the application is designed to store user input. The attacker would inject the code through requests to the application. After receiving this data, the application may then store the malicious code on the server or in a database. Hence the name stored XSS.
Why is stored XSS important?
The reason for that is that the reach of the malicious code through stored XSS is enormous. It takes fewer resources to target a larger number of victims. And once the malicious code is in place, its effect is continuous.
What happens if XSS isn't identified?
If stored XSS isn’t identified and mitigated, the malicious code will keep doing its job for a ton of users and can go on for decades. Another advantage of stored XSS is that even if infected, users have no way to know they should be careful.
How to avoid XSS?
So the straightforward approach to avoid XSS vulnerabilities is to sanitize user data and handle inputs safely. Let’s look at an example and understand how sanitizing data would mitigate XSS.
Why does malicious code execute?
The reason the malicious code executes was that the input wasn’t sanitized.
What are the advantages of XSS?
Another advantage of stored XSS is that even if infected, users have no way to know they should be careful. For example, Facebook is a well-established platform. It’s been around for a long time and has developed a factor of trust within users. You wouldn’t think a lot before opening a post on Facebook because you believe it can be trusted. But you would think twice before opening a link to/from an unknown application/email (like in the case of reflected XSS) just because you don’t know if it’s safe. If such well-established applications are vulnerable to stored XSS, it makes it even easier for the attackers to lengthen their victim list.
Stored Cross-Site Scripting Explained
- In a Stored XSS attack, the vulnerable web application receives user-supplied input from untrusted sources and stores it. This malicious content also gets included in the later HTTP responses sent by the server. To perform a Stored XSS attack, hackers only need to identify a security vulnerability within the backend application that allows for the ...
Stored XSS Payloads
- A persistent attack aims to inject bad code into popular user-supplied input points, such as comments on blog posts, username fields, and message boards. The payload enables the malicious user to bypass XSS filters and input validation checks. Knowledge of these payloads is essential for application security professionals looking to test and mitigate the stored XSS vulne…
Preventing Stored XSS Vulnerabilities
- Below are the ways to prevent hackers from exploiting the stored XSS vulnerability in a web application:
FAQs
- What can you do with Stored XSS?
By arbitrarily executing JavaScript, attackers can do varying levels of damage depending on the accounts hacked and the sensitivity of exposed data. Some expected consequences of stored XSS attacks include: 1. Identity theft 2. Website vandalism 3. Denial-of-service attacks 4. Sessio… - What are the differences between DOM-based and Persistent XSS?
In DOM-based XSS, attackers input malicious code into the Document Object Model (DOM) part, which is processed unsafely by the client-side environment. This type of attack can be persistent or non-persistent XSS. When attackers leverage the backend application to control part of the ab…
What Is Stored Cross-Site Scripting?
- Stored cross-site scripting (also known as second-order or persistent XSS) arises when an application receives data from an untrusted source and includes that data within its later HTTP responses in an unsafe way. Suppose a website allows users to submit comments on blog posts, which are displayed to other users. Users submit comments using an HTTP request like the follo…
Impact of Stored XSS Attacks
- If an attacker can control a script that is executed in the victim's browser, then they can typically fully compromise that user. The attacker can carry out any of the actions that are applicable to the impact of reflected XSS vulnerabilities. In terms of exploitability, the key difference between reflected and stored XSS is that a stored XSS vulne...
Stored XSS in Different Contexts
- There are many different varieties of stored cross-site scripting. The location of the stored data within the application's response determines what type of payload is required to exploit it and might also affect the impact of the vulnerability. In addition, if the application performs any validation or other processing on the data before it is stored, or at the point when the stored dat…
How to Find and Test For Stored XSS Vulnerabilities
- Many stored XSS vulnerabilities can be found using Burp Suite's web vulnerability scanner. Testing for stored XSS vulnerabilities manually can be challenging. You need to test all relevant "entry points" via which attacker-controllable data can enter the application's processing, and all "exit points" at which that data might appear in the application's responses. Entry points into the …
Overview
- Cross-Site Scripting (XSS) attacks are a type of injection, in whichmalicious scripts are injected into otherwise benign and trustedwebsites. XSS attacks occur when an attacker uses a web application tosend malicious code, generally in the form of a browser side script, toa different end user. Flaws that allow these attacks to succeed arequite wide...
Related Security Activities
- How to Avoid Cross-site scripting Vulnerabilities
1. XSS (Cross Site Scripting) Prevention Cheat Sheet 2. DOM based XSS Prevention Cheat Sheet 3. OWASP Development Guide article on Data Validation 4. OWASP Development Guide article on Phishing - How to Review Code for Cross-site scripting Vulnerabilities
See the OWASP Code Review Guide.
Description
- Cross-Site Scripting (XSS) attacks occur when: 1. Data enters a Web application through an untrusted source, most frequently a web request. 2. The data is included in dynamic content that is sent to a web user without being validated for malicious content. The malicious content sent to the web browser often takes the form of asegment of JavaScript, but may also include HTML, Fl…
Examples
- Cross-site scripting attacks may occur anywhere that possibly malicioususers are allowed to post unregulated material to a trusted website forthe consumption of other valid users. The most common example can be found in bulletin-board websites whichprovide web based mailing list-style functionality.
Related Attacks
Related Vulnerabilities
- Improper Data Validation
- Types of Cross-Site Scripting
- OWASP Development Guide article on Data Validation
- OWASP Development Guide article on Phishing
References
- OWASP’s XSS (Cross Site Scripting) Prevention Cheat Sheet
- Testing_for_Reflected_Cross_site_scripting
- Testing_for_Stored_Cross_site_scripting
- Testing_for_DOM-based_Cross_site_scripting