| Attack Pattern ID | Pattern Abstraction: Standard 62 |
| Typical Severity | Very High |
| Description | Summary
An attacker crafts malicious web links and distributes them (via web pages, email, etc.), typically in a targeted manner, hoping to induce users to click on the link and execute the malicious action against some third-party application. If successful, the action embedded in the malicious link will be processed and accepted by the targeted application with the users’ privilege level.
This type of attack leverages the persistence and implicit trust placed in user session cookies by many web applications today. In such an architecture, once the user authenticates to an application and a session cookie is created on the user's system, all following transactions for that session are authenticated using that cookie including potential actions initiated by an attacker and simply "riding" the existing session cookie.
Attack Execution Flow Explore Explore target website: The attacker first explores the target website to determine pieces of functionality that are of interest to him (e.g. money transfers). The attacker will need a legitimate user account on the target website. It would help to have two accounts. |
Attack Step Techniques |
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| Description | Environments |
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| Use web application debugging tool such as WebScarab, Tamper Data or TamperIE to analyze the information exchanged between the client and the server | env-Web | | Use network sniffing tool such as Wireshark to analyze the information exchanged between the client and the server | env-Web | | View HTML source of web pages that contain links or buttons that perform actions of interest. | env-Web |
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Outcomes |
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| ID | Type | Description |
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| c62s1o1 | Success | Attacker identifies at least one piece of interesting functionality that can be executed by making a single HTTP GET or POST request containing no session-specific parameters. | | c62s1o2 | Failure | Attacker cannot identify any functionality that can be executed without sending a session-specific parameter other than the cookie in the HTTP request. |
Experiment Create a link that when clicked on, will execute the interesting functionality.: The attacker needs to create a link that will execute some interesting functionality such as transfer money, change a password, etc. |
Attack Step Techniques |
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| Description | Environments |
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| Create a GET request containing all required parameters (e.g. https://www.somebank.com/members/transfer.asp?to=012345678901&amt=10000) | env-Web | | Create a form that will submit a POST request (e.g. <form method="POST" action="https://www.somebank.com/members/transfer.asp"><input type="hidden" Name="to" value="012345678901"/><input type="hidden" Name="amt" value="10000"/><input type="submit" src="clickhere.jpg"/></form> | env-Web |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
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| c62s2i1 | Positive | Success outcome in previous step. | env-Web | | c62s2i2 | Negative | Failure outcome in previous step. | env-Web |
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Outcomes |
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| ID | Type | Description |
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| c62s2o1 | Success | A link that performs an operation that the attacker desires when it is clicked. | | c62s2o2 | Failure | Creating a link that performs an operation that the attacker desires when it is clicked, is impossible, because the site has implemented protections against CSRF. |
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Security Controls |
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| ID | Type | Description |
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| c62s2sc1 | Preventative | Include a unique HTTP parameter value in forms every time they are sent to the client. Verify that the expected value is in the response received from the client. In this case, the attacker will not have access to the correct parameter value for another user, and thus, will not be able to create forged requests. | | c62s2sc2 | Preventative | Check HTTP referrer for each request to ensure that it is from the expected site. Note that if the site is vulnerable to XSS, then the attacker will be able to bypass this. |
Exploit Convince user to click on link: Finally, the attacker needs to convince a user that is logged into the target website to click on a link to execute the CSRF attack. |
Attack Step Techniques |
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| Description | Environments |
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| Execute a phishing attack and send the user an e-mail convincing him to click on a link. | env-Web | | Execute a stored XSS attack on a website to permanently embed the malicious link into the website. | env-Web | | Execute a stored XSS attack on a website where a XMLHTTPRequest object will automatically execute the attack as soon as a user visits the page. This removes the step of convincing a user to click on a link. | env-Web | | Include the malicious link on the attacker's own website where the user may have to click on the link, or where an XMLHTTPRequest object may automatically execute the attack when a user visits the site. | env-Web |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
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| c62s3i1 | Positive | Success outcome in previous step. | env-Web | | c62s3i2 | Negative | Failure outcome in previous step. | env-Web |
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Outcomes |
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| ID | Type | Description |
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| c62s3o1 | Success | A user executes the malicious link crafted by the attacker. | | c62s3o2 | Failure | Failure outcome in previous step. |
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Security Controls |
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| ID | Type | Description |
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| c62s3sc1 | Detective | Monitor server logs for referrers. If users are being tricked into clicking CSRF links through forums or other web postings, their web browsers will be providing Referer headers most of the time. These can help indicate that the actual request is illegitimate. | | c62s3sc2 | Corrective | Deny requests and invalidate session IDs for requests that contain unexpected referrers. Note that this will not protect against cases where the target website is also vulnerable to cross site scripting. |
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| Typical Likelihood of Exploit |
High
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| Methods of Attack | |
| Examples-Instances | Description While a user is logged into his bank account, an attacker can send an email with some potentially interesting content and require the user to click on a link in the email.
The link points to or contains an attacker setup script, probably even within an iFrame, that mimicks an actual user form submission to perform a malicious activity, such as transferring funds from the victim's account.
The attacker can have the script embedded in, or targeted by, the link perform any arbitrary action as the authenticated user. When this script is executed, the targeted application authenticates and accepts the actions based on the victims existing session cookie.
Related Vulnerability Cross-site request forgery (CSRF) vulnerability in util.pl in @Mail WebMail 4.51 allows remote attackers to modify arbitrary settings and perform unauthorized actions as an arbitrary user, as demonstrated using a settings action in the SRC attribute of an IMG element in an HTML e-mail. |
| Attacker Skill or Knowledge Required | Medium: The attacker needs to figure out the exact invocation of the targeted malicious action and then craft a link that performs the said action. Having the user click on such a link is often accomplished by sending an email or posting such a link to a bulletin board or the likes. |
| Resources Required | All the attacker needs is the exact representation of requests to be made to the application and to be able to get the malicious link across to a victim. |
| Probing Techniques | The attacker can observe the way the application accepts requests for actions. If the application uses a persistent cookie, a non-random identifier or any such static identification token that does not change with every request, the attack is fairly straightforward to accomplish |
| Obfuscation Techniques | In order to obfuscate the actual URL and its contents passed to the victim, the attacker can employ a service such as TinyURL and optionally redirect the request to the actual malicious script |
| Solutions and Mitigations | Use cryptographic tokens to associate a request with a specific action. The token can be regenerated at every request so that if a request with an invalid token is encountered, it can be reliably discarded. The token is considered invalid if it arrived with a request other than the action it was supposed to be associated with. Although less reliable, the use of the optional HTTP Referer header can also be used to determine whether an incoming request was actually one that the user is authorized for, in the current context. Additionally, the user can also be prompted to confirm an action every time an action concerning potentially sensitive data is invoked. This way, even if the attacker manages to get the user to click on a malicious link and request the desired action, the user has a chance to recover by denying confirmation. This solution is also implicitly tied to using a second factor of authentication before performing such actions. In general, every request must be checked for the appropriate authentication token as well as authorization in the current session context. |
| Attack Motivation-Consequences | - Privilege Escalation
- Information Leakage
- Data Modification
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| Context Description |
Cross Site Request Forgery is possible in a context where the vulnerable application does not authenticate every request.
Such applications rely on a persistent cookie or some such static identifier to identify and authenticate the user. In addition, there is no authorization to check the requested action.
This enables the attacker to perform actions in an authenticated context since the relevant cookies or identifiers are automatically tacked on by the browser to the request.
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| Related Weaknesses | | CWE-ID | Weakness Name | Weakness Relationship Type |
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| 352 | Cross-Site Request Forgery (CSRF) | Targeted | | 306 | No Authentication for Critical Function | Secondary |
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| Related Security Principles | - Complete Mediation
- Defense In Depth
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| Related Guidelines | - Use Authorization Mechanisms Correctly
- Use Authentication Mechanisms, Where Appropriate, Correctly
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| Purpose | Exploitation |
| CIA Impact | | Confidentiality Impact | Integrity Impact | Availability Impact |
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| High | High | Low |
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| Technical Context | | Architectural Paradigm | Framework | Platform | Language |
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| Client-Server | J2EE | All | All |
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| References | "Session Riding: A Widespread Vulnerability in Today's Web Applications", Thomas Schreiber, SecureNet GmbH, Dec 2004. http://www.securenet.de/papers/Session_Riding.pdf |
| Source | | Submission(s) |
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| Submitter | Organization | Date | Comment |
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| Chiradeep B.Chhaya | Cigital, Inc | 2007-02-27 | |
| Modification(s) |
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| Modifier | Organization | Date | Comment |
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| Richard Struse | VOXEM, Inc | 2007-03-26 | Review and feedback leading to changes in Description and Related Attack Patterns | | Sean Barnum | Cigital, Inc | 2007-04-13 | Modified pattern content according to review and feedback | | Amit Sethi | Cigital, Inc. | 2007-10-29 | Added extended Attack Execution Flow |
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