Compound Element ID: 352 (Compound Element Variant: Composite)
Description
Summary
The web application does not, or can not, sufficiently verify
whether a well-formed, valid, consistent request was intentionally provided by
the user who submitted the request.
Extended Description
When a web server is designed to receive a request from a client without
any mechanism for verifying that it was intentionally sent, then it might be
possible for an attacker to trick a client into making an unintentional
request to the web server which will be treated as an authentic request.
This can be done via a URL, image load, XMLHttpRequest, etc. and can result
in data disclosure or unintended code execution.
Alternate Terms
Session Riding
Cross Site Reference Forgery
XSRF
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
All
Technology Classes
Web-Server
Likelihood of Exploit
High
Demonstrative Examples
This example PHP code attempts to secure the form submission process
by validating that the user submitting the form has a valid session. A CSRF
attack would not be prevented by this countermeasure because the attacker
forges a request through the user's web browser in which a valid session
already exists.
The following HTML is intended to allow a user to update a
profile.
echo "Your profile has been successfully updated.";
}
This code may look protected since it checks for a valid session.
However, CSRF attacks can be staged from virtually any tag or HTML
construct, including image tags, links, embed or object tags, or other
attributes that load background images.
The attacker can then host code that will silently change the username
and email address of any user that visits the page while remaining
logged in to the target web application. The code might be an
innocent-looking web page such as:
Notice how the form contains hidden fields, so when it is loaded into
the browser, the user will not notice it. Because SendAttack() is
defined in the body's onload attribute, it will be automatically called
when the victim loads the web page.
Assuming that the user is already logged in to victim.example.com,
profile.php will see that a valid user session has been established,
then update the email address to the attacker's own address. At this
stage, the user's identity has been compromised, and messages sent
through this profile could be sent to the attacker's address.
Change another users settings via a URL or an img
tag
Potential Mitigations
Architecture and Design
Use anti-CSRF packages such as the OWASP CSRFGuard.
Implementation
Ensure that your 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).
Note that this can be bypassed using XSS (CWE-79).
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.
Note that this can be bypassed using XSS (CWE-79).
Architecture and Design
Use the "double-submitted cookie" method as described by Felten and
Zeller.
Note that this can probably be bypassed using XSS (CWE-79).
Architecture and Design
Use the ESAPI Session Management control.
This control includes a component for CSRF.
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.
Note that this can be bypassed using XSS (CWE-79). An attacker could
use XSS to generate a spoofed Referer, or to generate a malicious
request from a page whose Referer would be allowed.
Testing
Use tools and techniques that require manual (human) analysis, such as
penetration testing, threat modeling, and interactive tools that allow
the tester to record and modify an active session. These may be more
effective than strictly automated techniques. This is especially the
case with weaknesses that are related to design and business
rules.
Use OWASP CSRFTester to identify potential issues.
Description
Architecture and Design
