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Cross-site request forgery
Cross-site request forgery, also known as one-click attack or session riding and abbreviated as CSRF (sometimes pronounced sea-surf) or XSRF, is a type of malicious exploit of a website or web application where unauthorized commands are submitted from a user that the web application trusts. There are many ways in which a malicious website can transmit such commands; specially-crafted image tags, hidden forms, and JavaScript fetch or XMLHttpRequests, for example, can all work without the user's interaction or even knowledge. Unlike cross-site scripting (XSS), which exploits the trust a user has for a particular site, CSRF exploits the trust that a site has in a user's browser. In a CSRF attack, an innocent end user is tricked by an attacker into submitting a web request that they did not intend. This may cause actions to be performed on the website that can include inadvertent client or server data leakage, change of session state, or manipulation of an end user's account.
The term "CSRF" is also used as an abbreviation in defences against CSRF attacks, such as techniques that use header data, form data, or cookies, to test for and prevent such attacks.
In a CSRF attack, the attacker's goal is to cause an innocent victim to unknowingly submit a maliciously crafted web request to a website that the victim has privileged access to. This web request can be crafted to include URL parameters, cookies and other data that appear normal to the web server processing the request. At risk are web applications that perform actions based on input from trusted and authenticated users without requiring the user to authorize (e.g. via a popup confirmation) the specific action. A user who is authenticated by a cookie saved in the user's web browser could unknowingly send an HTTP request to a site that trusts the user and thereby cause an unwanted action.
A general property of web browsers is that they will automatically and invisibly include any cookies (including session cookies and others) used by a given domain in any web request sent to that domain. This property is exploited by CSRF attacks. In the event that a user is tricked into inadvertently submitting a request through their browser these automatically included cookies will cause the forged request to appear real to the web server and it will perform any appropriately requested actions including returning data, manipulating session state, or making changes to the victim's account.
In order for a CSRF attack to work, an attacker must identify a reproducible web request that executes a specific action such as changing an account password on the target page. Once such a request is identified, a link can be created that generates this malicious request and that link can be embedded on a page within the attacker's control. This link may be placed in such a way that it is not even necessary for the victim to click the link. For example, it may be embedded within an html image tag on an email sent to the victim which will automatically be loaded when the victim opens their email. Once the victim has clicked the link, their browser will automatically include any cookies used by that website and submit the request to the web server. The web server will not be able to identify the forgery because the request was made by a user that was logged in, and submitted all the requisite cookies.
Cross-site request forgery is an example of a confused deputy attack against a web browser because the web browser is tricked into submitting a forged request by a less privileged attacker.
CSRF commonly has the following characteristics:
CSRF Token vulnerabilities have been known and in some cases exploited since 2001. Because it is carried out from the user's IP address, some website logs might not have evidence of CSRF. Exploits are under-reported, at least publicly, and as of 2007 there were few well-documented examples:
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Cross-site request forgery AI simulator
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Cross-site request forgery
Cross-site request forgery, also known as one-click attack or session riding and abbreviated as CSRF (sometimes pronounced sea-surf) or XSRF, is a type of malicious exploit of a website or web application where unauthorized commands are submitted from a user that the web application trusts. There are many ways in which a malicious website can transmit such commands; specially-crafted image tags, hidden forms, and JavaScript fetch or XMLHttpRequests, for example, can all work without the user's interaction or even knowledge. Unlike cross-site scripting (XSS), which exploits the trust a user has for a particular site, CSRF exploits the trust that a site has in a user's browser. In a CSRF attack, an innocent end user is tricked by an attacker into submitting a web request that they did not intend. This may cause actions to be performed on the website that can include inadvertent client or server data leakage, change of session state, or manipulation of an end user's account.
The term "CSRF" is also used as an abbreviation in defences against CSRF attacks, such as techniques that use header data, form data, or cookies, to test for and prevent such attacks.
In a CSRF attack, the attacker's goal is to cause an innocent victim to unknowingly submit a maliciously crafted web request to a website that the victim has privileged access to. This web request can be crafted to include URL parameters, cookies and other data that appear normal to the web server processing the request. At risk are web applications that perform actions based on input from trusted and authenticated users without requiring the user to authorize (e.g. via a popup confirmation) the specific action. A user who is authenticated by a cookie saved in the user's web browser could unknowingly send an HTTP request to a site that trusts the user and thereby cause an unwanted action.
A general property of web browsers is that they will automatically and invisibly include any cookies (including session cookies and others) used by a given domain in any web request sent to that domain. This property is exploited by CSRF attacks. In the event that a user is tricked into inadvertently submitting a request through their browser these automatically included cookies will cause the forged request to appear real to the web server and it will perform any appropriately requested actions including returning data, manipulating session state, or making changes to the victim's account.
In order for a CSRF attack to work, an attacker must identify a reproducible web request that executes a specific action such as changing an account password on the target page. Once such a request is identified, a link can be created that generates this malicious request and that link can be embedded on a page within the attacker's control. This link may be placed in such a way that it is not even necessary for the victim to click the link. For example, it may be embedded within an html image tag on an email sent to the victim which will automatically be loaded when the victim opens their email. Once the victim has clicked the link, their browser will automatically include any cookies used by that website and submit the request to the web server. The web server will not be able to identify the forgery because the request was made by a user that was logged in, and submitted all the requisite cookies.
Cross-site request forgery is an example of a confused deputy attack against a web browser because the web browser is tricked into submitting a forged request by a less privileged attacker.
CSRF commonly has the following characteristics:
CSRF Token vulnerabilities have been known and in some cases exploited since 2001. Because it is carried out from the user's IP address, some website logs might not have evidence of CSRF. Exploits are under-reported, at least publicly, and as of 2007 there were few well-documented examples: