Introduction to Cross-Site Request Forgery (CSRF) Attacks
Cross-Site Request Forgery (CSRF) is a security vulnerability that allows an attacker to trick a user into performing unwanted actions on a web application, without their consent. In a CSRF attack, the user’s browser is used as a conduit for unauthorized requests to a vulnerable application, effectively exploiting the user’s authenticated session.
The Importance of Protecting Against CSRF Attacks
If a web application is not protected against CSRF attacks, it can lead to serious consequences, including:
- Unauthorized data modification or deletion
- Unauthorized account access or password changes
- Unauthorized financial transactions
To keep your Node Express applications secure, it’s essential to implement proper CSRF protection measures.
Implementing CSRF Protection in Express
In this article, we’ll walk through the process of implementing CSRF protection for a Node Express web application, using the following steps:
- Installing necessary packages
- Setting up middleware
- Generating CSRF tokens
- Validating CSRF tokens
- Handling token errors
Step 1: Installing Necessary Packages
First, you’ll need to install two packages to help implement CSRF protection: csurf
and cookie-parser
. To do this, run the following command in your terminal:
1 2 | <span class="token function">npm</span> <span class="token function">install</span> csurf cookie-parser |
Step 2: Setting Up Middleware
After installing the packages, you’ll need to set up the middleware in your Express.js application. Import the csurf
and cookie-parser
packages and add them to your middleware stack:
1 2 3 4 5 6 7 8 9 | <span class="token keyword">const</span> express <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'express'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">const</span> cookieParser <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'cookie-parser'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">const</span> csrf <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'csurf'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">const</span> app <span class="token operator">=</span> <span class="token function">express</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> app<span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span><span class="token function">cookieParser</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> app<span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span><span class="token function">csrf</span><span class="token punctuation">(</span><span class="token punctuation">{</span> cookie<span class="token operator">:</span> <span class="token boolean">true</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
Step 3: Generating CSRF Tokens
Next, you need to generate CSRF tokens for each user session. To do this, include the csrfToken
function in your route handlers:
1 2 3 4 5 | app<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">'/form'</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token parameter">req<span class="token punctuation">,</span> res</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span> <span class="token keyword">const</span> csrfToken <span class="token operator">=</span> req<span class="token punctuation">.</span><span class="token function">csrfToken</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> res<span class="token punctuation">.</span><span class="token function">render</span><span class="token punctuation">(</span><span class="token string">'form'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span> csrfToken <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
Include the generated CSRF token as a hidden field in your HTML forms:
1 2 3 4 5 6 | <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>form</span> <span class="token attr-name">action</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>/submit<span class="token punctuation">"</span></span> <span class="token attr-name">method</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>POST<span class="token punctuation">"</span></span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>input</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>hidden<span class="token punctuation">"</span></span> <span class="token attr-name">name</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>_csrf<span class="token punctuation">"</span></span> <span class="token attr-name">value</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>{{csrfToken}}<span class="token punctuation">"</span></span><span class="token punctuation">></span></span> <span class="token comment"><!-- other form fields go here --></span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>button</span> <span class="token attr-name">type</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">"</span>submit<span class="token punctuation">"</span></span><span class="token punctuation">></span></span>Submit<span class="token tag"><span class="token tag"><span class="token punctuation"></</span>button</span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"></</span>form</span><span class="token punctuation">></span></span> |
Step 4: Validating CSRF Tokens
The csurf
middleware automatically validates the CSRF tokens in incoming POST requests. If the token is valid, the request will proceed as normal. If the token is missing or incorrect, an error will be thrown.
Step 5: Handling Token Errors
To handle CSRF token errors gracefully, you can add a custom error handler to your Express.js application:
1 2 3 4 5 6 7 8 9 10 | app<span class="token punctuation">.</span><span class="token function">use</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">err<span class="token punctuation">,</span> req<span class="token punctuation">,</span> res<span class="token punctuation">,</span> next</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>err<span class="token punctuation">.</span>code <span class="token operator">===</span> <span class="token string">'EBADCSRFTOKEN'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// CSRF token validation failed</span> res<span class="token punctuation">.</span><span class="token function">status</span><span class="token punctuation">(</span><span class="token number">403</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">send</span><span class="token punctuation">(</span><span class="token string">'Invalid CSRF token.'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span> <span class="token comment">// Pass the error to the next middleware</span> <span class="token function">next</span><span class="token punctuation">(</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
This will catch CSRF token errors and return a 403 Forbidden response with a helpful message.
Conclusion
By following these steps, you can effectively protect your Nodejs Express web applications from Cross-Site Request Forgery attacks. Remember to keep your packages up-to-date and monitor your application’s security regularly to ensure that it remains safe from vulnerabilities.
And Finally
As always, I hope you enjoyed this article and got something new.
Thank you and see you in the next articles!
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