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CWE-784: Reliance on Cookies without Validation and Integrity Checking in a Security Decision
 DescriptionDescription 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
Applicable PlatformsLanguages Language-independent Architectural Paradigms Web-based: (Often) Common Consequences
Likelihood of ExploitHigh Demonstrative ExamplesExample 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
Potential Mitigations
Relationships
References
Maintenance Notes
Content History
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Page Last Updated:
February 20, 2013
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