Common Weakness Enumeration

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

Weakness ID: 784
Abstraction: Variant
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
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.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
+ Relevant to the view "Architectural Concepts" (CWE-1008)
MemberOfCategoryCategory1012Cross Cutting
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory442Web Problems
ChildOfBaseBase565Reliance on Cookies without Validation and Integrity Checking
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and DesignOMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)


Web Based (Often Prevalent)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Access Control

Technical Impact: Bypass Protection Mechanism; Gain Privileges or 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
+ 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 {



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
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.
+ 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.
+ References
[REF-706] Steve Christey. "Unforgivable Vulnerabilities". 2007-08-02. <>.
[REF-7] Michael Howard and David LeBlanc. "Writing Secure Code". Chapter 13, "Sensitive Data in Cookies and Fields" Page 435. 2nd Edition. Microsoft Press. 2002-12-04. <>.
+ Content History
Submission DateSubmitterOrganization
2009-07-16CWE Content TeamMITRE
Modification DateModifierOrganization
2009-10-29CWE Content TeamMITRE
updated Relationships
2010-02-16CWE Content TeamMITRE
updated Demonstrative_Examples, References, Relationships
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2017-01-19CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Modes_of_Introduction, References, Relationships

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Page Last Updated: January 18, 2018