**Course Title:** Security Best Practices in Software Development **Section Title:** Common Vulnerabilities and Attacks **Topic:** Cross-Site Request Forgery (CSRF) and how to prevent it. **Overview of Cross-Site Request Forgery (CSRF)** ===================================================== Cross-Site Request Forgery (CSRF) is a type of security vulnerability that occurs when an attacker tricks a user into performing unintended actions on a web application that the user is authenticated to. CSRF attacks can have serious consequences, such as unauthorized transactions, data breaches, and compromised user accounts. **How CSRF Works** ------------------- A CSRF attack typically involves the following steps: 1. **Step 1:** An attacker identifies a web application that is vulnerable to CSRF attacks. 2. **Step 2:** The attacker creates a malicious request that mimics a legitimate request to the web application. 3. **Step 3:** The attacker tricks a user into sending the malicious request to the web application, often by embedding it in an email or a web page. 4. **Step 4:** The web application processes the malicious request, thinking it came from the legitimate user. **Example of a CSRF Attack** ----------------------------- Suppose we have an online banking application that allows users to transfer money between accounts. An attacker could create a malicious request that initiates a transfer from the user's account to the attacker's account. The malicious request might look like this: ```http POST /transfer HTTP/1.1 Host: bank.com Cookies: JSESSIONID=1234567890 Account_number=1234567890&Amount=1000&Destination_account= attacker_account ``` If the user is logged in to the online banking application and clicks on the malicious request, the application will process the request and transfer the money to the attacker's account. **Prevention Techniques** --------------------------- To prevent CSRF attacks, web applications can use the following techniques: ### **1. Token-based validation** The web application generates a random token for each user session and includes it in every request. When the server receives a request, it checks the token to ensure it matches the one stored in the user's session. If the tokens do not match, the request is rejected. **Example of Token-based Validation** ------------------------------------- Here's an example of how token-based validation can be implemented: * On every request, the server generates a random token and stores it in the user's session: ```http Setsessiontoken= ABCDEFGHIJKLMNO ``` * The server includes the token in every form: ```html <input type="hidden" name="token" value=" ABCDEFGHIJKLMNO"> ``` * When the server receives a request, it checks the token: ```http if request.token == sessiontoken: process_request() else: reject_request() ``` ### **2. Double-submit cookie** The web application sets a cookie on the user's browser with a random value. When the user submits a request, the web application checks the cookie to ensure it matches the one stored in the user's session. If the cookies do not match, the request is rejected. **Example of Double-submit Cookie** ------------------------------------ Here's an example of how double-submit cookie can be implemented: * The server sets a random cookie on the user's browser: ```http Set-Cookie: CSRF-Token= ABCDEFGHIJKLMNO ``` * The server includes the cookie value in every form: ```html <input type="hidden" name="token" value=" ABCDEFGHIJKLMNO"> ``` * When the server receives a request, it checks the cookie: ```http if request.token == cookie: process_request() else: reject_request() ``` ### **3. Same-site cookie** The same-site cookie is a cookie set by the web application with the `SameSite` attribute set to `Strict` or `Lax`. This attribute instructs the browser to only include the cookie in requests to the same site that set the cookie. **Example of Same-site Cookie** ------------------------------- Here's an example of how same-site cookie can be implemented: * The server sets a same-site cookie on the user's browser: ```http Set-Cookie: CSRF-Token= ABCDEFGHIJKLMNO; SameSite=Strict ``` * When the browser sends a request to the web application, it includes the cookie: ```http POST /transfer HTTP/1.1 Host: bank.com Cookies: CSRF-Token= ABCDEFGHIJKLMNO ``` * The server checks the cookie to ensure it is present: ```http if request.cookie == "CSRF-Token= ABCDEFGHIJKLMNO": process_request() else: reject_request() ``` ### **4. Origin header validation** The web application checks the `Origin` header in every request to ensure it matches the expected origin. **Example of Origin Header Validation** -------------------------------------- Here's an example of how origin header validation can be implemented: * When the browser sends a request to the web application, it includes the origin header: ```http POST /transfer HTTP/1.1 Host: bank.com Origin: https://bank.com ``` * The server checks the origin header to ensure it matches the expected origin: ```http if request.origin == "https://bank.com": process_request() else: reject_request() ``` **Additional Prevention Techniques** -------------------------------------- 1. **Reject unknown or invalid requests**: Web applications should reject requests that are unknown or invalid to prevent attackers from exploiting vulnerabilities. 2. **Use HTTPS**: Web applications should use HTTPS to encrypt requests and prevent man-in-the-middle attacks. 3. **Implement rate limiting**: Web applications should implement rate limiting to prevent brute-force attacks. 4. **Keep software up to date**: Web applications should keep their software up to date to prevent exploitation of known vulnerabilities. **Conclusion** ---------- In conclusion, CSRF is a serious security vulnerability that can have significant consequences for web applications and their users. To prevent CSRF attacks, web applications can use token-based validation, double-submit cookie, same-site cookie, and origin header validation. By implementing these prevention techniques, web applications can significantly reduce the risk of CSRF attacks. Additionally, web applications should reject unknown or invalid requests, use HTTPS, implement rate limiting, and keep software up to date to prevent other types of attacks. If you have any questions or would like to know more about how to prevent CSRF attacks, please leave a comment below or ask for help. **External Resources:** * [OWASP: Cross-Site Request Forgery (CSRF)](https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html) * [W3C: Same-site cookies](https://www.w3.org/TR/samesite/#same-site-origin) * [MDN Web Docs: Cross-Site Request Forgery (CSRF)](https://developer.mozilla.org/en-US/docs/Web/Security/Cross-site_request_forgery) **Next Topic:**Buffer overflow attacks and secure coding practices.