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ID

CWE-784: Reliance on Cookies without Validation and Integrity Checking in a Security Decision

Weakness ID: 784
Abstraction: Variant
Status: Draft
Presentation Filter:
+ Description

Description Summary

The application uses a protection mechanism that relies on the existence or values of a cookie, but it does not properly ensure that the cookie is valid for the associated user.

Extended Description

Attackers can easily modify cookies, within the browser or by implementing the client-side code outside of the browser. Attackers can bypass protection mechanisms such as authorization and authentication by modifying the cookie to contain an expected value.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

Architectural Paradigms

Web-based: (Often)

+ Common Consequences
ScopeEffect
Access Control

Technical Impact: Bypass protection mechanism; Gain privileges / assume identity

It is dangerous to use cookies to set a user's privileges. The cookie can be manipulated to claim a high level of authorization, or to claim that successful authentication has occurred.

+ Likelihood of Exploit

High

+ Demonstrative Examples

Example 1

The following code excerpt reads a value from a browser cookie to determine the role of the user.

(Bad Code)
Example Language: Java 
Cookie[] cookies = request.getCookies();
for (int i =0; i< cookies.length; i++) {
Cookie c = cookies[i];
if (c.getName().equals("role")) {
userRole = c.getValue();
}
}

Example 2

The following code could be for a medical records application. It performs authentication by checking if a cookie has been set.

(Bad Code)
Example Language: PHP 
$auth = $_COOKIES['authenticated'];
if (! $auth) {
if (AuthenticateUser($_POST['user'], $_POST['password']) == "success") {
// save the cookie to send out in future responses
setcookie("authenticated", "1", time()+60*60*2);
}
else {
ShowLoginScreen();
die("\n");
}
}
DisplayMedicalHistory($_POST['patient_ID']);

The programmer expects that the AuthenticateUser() check will always be applied, and the "authenticated" cookie will only be set when authentication succeeds. The programmer even diligently specifies a 2-hour expiration for the cookie.

However, the attacker can set the "authenticated" cookie to a non-zero value such as 1. As a result, the $auth variable is 1, and the AuthenticateUser() check is not even performed. The attacker has bypassed the authentication.

Example 3

In the following example, an authentication flag is read from a browser cookie, thus allowing for external control of user state data.

(Bad Code)
Example Language: Java 
Cookie[] cookies = request.getCookies();
for (int i =0; i< cookies.length; i++) {
Cookie c = cookies[i];
if (c.getName().equals("authenticated") && Boolean.TRUE.equals(c.getValue())) {
authenticated = true;
}
}
+ Observed Examples
ReferenceDescription
Attacker can bypass authentication by setting a cookie to a specific value.
Attacker can bypass authentication and gain admin privileges by setting an "admin" cookie to 1.
Content management system allows admin privileges by setting a "login" cookie to "OK."
e-dating application allows admin privileges by setting the admin cookie to 1.
Web-based email list manager allows attackers to gain admin privileges by setting a login cookie to "admin."
+ Potential Mitigations

Phase: Architecture and Design

Avoid using cookie data for a security-related decision.

Phase: Implementation

Perform thorough input validation (i.e.: server side validation) on the cookie data if you're going to use it for a security related decision.

Phase: Architecture and Design

Add integrity checks to detect tampering.

Phase: Architecture and Design

Protect critical cookies from replay attacks, since cross-site scripting or other attacks may allow attackers to steal a strongly-encrypted cookie that also passes integrity checks. This mitigation applies to cookies that should only be valid during a single transaction or session. By enforcing timeouts, you may limit the scope of an attack. As part of your integrity check, use an unpredictable, server-side value that is not exposed to the client.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory442Web Problems
Development Concepts699
ChildOfWeakness BaseWeakness Base565Reliance on Cookies without Validation and Integrity Checking
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness BaseWeakness Base807Reliance on Untrusted Inputs in a Security Decision
Research Concepts1000
+ References
Steve Christey. "Unforgivable Vulnerabilities". 2007-08-02. <http://cve.mitre.org/docs/docs-2007/unforgivable.pdf>.
[REF-11] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 13, "Sensitive Data in Cookies and Fields" Page 435. 2nd Edition. Microsoft. 2002.
+ Maintenance Notes

A new parent might need to be defined for this entry. This entry is specific to cookies, which reflects the significant number of vulnerabilities being reported for cookie-based authentication in CVE during 2008 and 2009. However, other types of inputs - such as parameters or headers - could also be used for similar authentication or authorization. Similar issues (under the Research view) include CWE-247 and CWE-472.

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
2009-07-16MITREInternal CWE Team
Modifications
Modification DateModifierOrganizationSource
2009-10-29CWE Content TeamMITREInternal
updated Relationships
2010-02-16CWE Content TeamMITREInternal
updated Demonstrative_Examples, References, Relationships
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2017-01-19CWE Content TeamMITREInternal
updated Relationships

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Page Last Updated: May 05, 2017