Cross-Site Request Forgery (CSRF)

Opis

The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.

Inne nazwy

Session Riding

Cross Site Reference Forgery

XSRF

CSRF

Skutki

• Confidentiality, Integrity, Availability, Non-Repudiation, Access Control

  Gain Privileges or Assume Identity; Bypass Protection Mechanism; Read Application Data; Modify Application Data; DoS: Crash, Exit, or Restart

  The consequences will vary depending on the nature of the functionality that is vulnerable to CSRF. An attacker could trick a client into making an unintentional request to the web server via a URL, image load, XMLHttpRequest, etc., which would then be treated as an authentic request from the client - effectively performing any operations as the victim, leading to an exposure of data, unintended code execution, etc. If the victim is an administrator or privileged user, the consequences may include obtaining complete control over the web application - deleting or stealing data, uninstalling the product, or using it to launch other attacks against all of the product's users. Because the attacker has the identity of the victim, the scope of CSRF is limited only by the victim's privileges.

Zapobieganie

• Architecture and Design · Libraries or Frameworks

  Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].

  For example, use anti-CSRF packages such as the OWASP CSRFGuard. [REF-330]

  Another example is the ESAPI Session Management control, which includes a component for CSRF. [REF-45]

• Implementation

  Ensure that the application is free of cross-site scripting issues (CWE-79), because most CSRF defenses can be bypassed using attacker-controlled script.

• Architecture and Design

  Generate a unique nonce for each form, place the nonce into the form, and verify the nonce upon receipt of the form. Be sure that the nonce is not predictable (CWE-330). [REF-332]

• Architecture and Design

  Identify especially dangerous operations. When the user performs a dangerous operation, send a separate confirmation request to ensure that the user intended to perform that operation.

• Architecture and Design

  Use the "double-submitted cookie" method as described by Felten and Zeller:

  When a user visits a site, the site should generate a pseudorandom value and set it as a cookie on the user's machine. The site should require every form submission to include this value as a form value and also as a cookie value. When a POST request is sent to the site, the request should only be considered valid if the form value and the cookie value are the same.

  Because of the same-origin policy, an attacker cannot read or modify the value stored in the cookie. To successfully submit a form on behalf of the user, the attacker would have to correctly guess the pseudorandom value. If the pseudorandom value is cryptographically strong, this will be prohibitively difficult.

  This technique requires Javascript, so it may not work for browsers that have Javascript disabled. [REF-331]

• Architecture and Design

  Do not use the GET method for any request that triggers a state change.

• Implementation

  Check the HTTP Referer header to see if the request originated from an expected page. This could break legitimate functionality, because users or proxies may have disabled sending the Referer for privacy reasons.

Przykłady podatności

• CVE-2004-1703 Add user accounts via a URL in an img tag
• CVE-2004-1995 Add user accounts via a URL in an img tag
• CVE-2004-1967 Arbitrary code execution by specifying the code in a crafted img tag or URL
• CVE-2004-1842 Gain administrative privileges via a URL in an img tag
• CVE-2005-1947 Delete a victim's information via a URL or an img tag
• CVE-2005-2059 Change another user's settings via a URL or an img tag
• CVE-2005-1674 Perform actions as administrator via a URL or an img tag
• CVE-2009-3520 modify password for the administrator
• CVE-2009-3022 CMS allows modification of configuration via CSRF attack against the administrator
• CVE-2009-3759 web interface allows password changes or stopping a virtual machine via CSRF

Słabość nadrzędna

• CWE-345 Insufficient Verification of Data Authenticity

Wymaga

• CWE-346 Origin Validation Error
• CWE-441 Unintended Proxy or Intermediary ('Confused Deputy')
• CWE-642 External Control of Critical State Data
• CWE-613 Insufficient Session Expiration

Kiedy powstaje

• Architecture and Design — REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Dotyczy

Not Language-Specific, Web Based, Web Server

Uwagi

There can be a close relationship between XSS and CSRF (CWE-352). An attacker might use CSRF in order to trick the victim into submitting requests to the server in which the requests contain an XSS payload. A well-known example of this was the Samy worm on MySpace [REF-956]. The worm used XSS to insert malicious HTML sequences into a user's profile and add the attacker as a MySpace friend. MySpace friends of that victim would then execute the payload to modify their own profiles, causing the worm to propagate exponentially. Since the victims did not intentionally insert the malicious script themselves, CSRF was a root cause.

The CSRF topology is multi-channel:

- Attacker (as outsider) to intermediary (as user). The interaction point is either an external or internal channel.

- Intermediary (as user) to server (as victim). The activation point is an internal channel.

Źródła

1. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 2: Web-Server Related Vulnerabilities (XSS, XSRF, and Response Splitting)." Page 37, McGraw-Hill, 2010
2. Cross-Site Request Forgeries (Re: The Dangers of Allowing Users to Post Images) — Peter W, Bugtraq
3. Cross-Site Request Forgery (CSRF) Prevention Cheat Sheet — OWASP
4. Cross-Site Request Forgeries: Exploitation and Prevention — Edward W. Felten, William Zeller, 2008
5. CSRF - The Cross-Site Request Forgery (CSRF/XSRF) FAQ — Robert Auger
6. Cross-site request forgery — Wikipedia, 2008
7. Top 25 Series - Rank 4 - Cross Site Request Forgery — Jason Lam, SANS Software Security Institute, 2010
8. Preventing CSRF and XSRF Attacks — Jeff Atwood, 2008
9. OWASP Enterprise Security API (ESAPI) Project — OWASP
10. Samy (computer worm) — Wikipedia
11. State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation — Gregory Larsen, E. Kenneth Hong Fong, David A. Wheeler, Rama S. Moorthy, 2014
12. D3FEND: D3-TL Trusted Library — D3FEND