What is CSRF?

CSRF (Cross-Site Request Forgery) is an attack in which the attacker makes a user's browser perform an action on a site without their knowledge, using an already authorized session.

In simple terms: the site thinks the user is performing the action, but it was actually triggered by the attacker.

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#How CSRF works in simple terms

1. The user is logged in to a site (for example, online banking)
2. The session is active (cookies are stored in the browser)
3. The user visits a malicious site
4. That site quietly sends a request to the trusted site
5. The browser automatically attaches the cookies
6. The server performs the action, thinking it is the user

The core problem: the site's trust in the user's browser.

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#What a CSRF attack can do

• change a password;
• change an email address;
• transfer money;
• change account settings;
• perform any action without confirmation.

CSRF does not steal data directly, it forces actions to be performed.

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#A CSRF example in simple terms

You:

• are logged in to a bank,
• open another site,
• and that site "presses the button" in the bank for you.

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#How CSRF differs from XSS

Important for the interview.

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#Which security properties are violated

• Integrity - unauthorized data changes;
• sometimes Confidentiality - indirectly.

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#How to defend against CSRF

#Main defense measures:

• CSRF tokens (the main one);
• checking Origin / Referer;
• SameSite cookies;
• confirming critical actions;
• re-authentication.

A CSRF token is the key defense.