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Variant · Low-Medium

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

The product 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.

CWE-784 · Variant Level ·5 CVEs ·4 Mitigations

Description

The product 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.

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.

Potential Impact

Access Control

Bypass Protection Mechanism, Gain Privileges or Assume Identity

Demonstrative Examples

The following code excerpt reads a value from a browser cookie to determine the role of the user.
Bad
Cookie[] cookies = request.getCookies();for (int i =0; i< cookies.length; i++) {Cookie c = cookies[i];if (c.getName().equals("role")) {userRole = c.getValue();}}
The following code could be for a medical records application. It performs authentication by checking if a cookie has been set.
Bad
$auth = $_COOKIES['authenticated'];if (! $auth) {if (AuthenticateUser($_POST['user'], $_POST['password']) == "success") {// save the cookie to send out in future responsessetcookie("authenticated", "1", time()+60*60*2);}else {ShowLoginScreen();die("\n");}}DisplayMedicalHistory($_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.
In the following example, an authentication flag is read from a browser cookie, thus allowing for external control of user state data.
Bad
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;}}

Mitigations & Prevention

Architecture and Design

Avoid using cookie data for a security-related decision.

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.

Architecture and Design

Add integrity checks to detect tampering.

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.

Real-World CVE Examples

CVE IDDescription
CVE-2009-1549Attacker can bypass authentication by setting a cookie to a specific value.
CVE-2009-1619Attacker can bypass authentication and gain admin privileges by setting an "admin" cookie to 1.
CVE-2009-0864Content management system allows admin privileges by setting a "login" cookie to "OK."
CVE-2008-5784e-dating application allows admin privileges by setting the admin cookie to 1.
CVE-2008-6291Web-based email list manager allows attackers to gain admin privileges by setting a login cookie to "admin."

CWE-807: Reliance on Untrusted Inputs in a Security Decision

The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modifie...

CWE-565: Reliance on Cookies without Validation and Integrity Checking

The product relies on the existence or values of cookies when performing security-critical operations, but it does not p...

Frequently Asked Questions

What is CWE-784?

CWE-784 (Reliance on Cookies without Validation and Integrity Checking in a Security Decision) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product 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.

How can CWE-784 be exploited?

Attackers can exploit CWE-784 (Reliance on Cookies without Validation and Integrity Checking in a Security Decision) to bypass protection mechanism, gain privileges or assume identity. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-784?

Key mitigations include: Avoid using cookie data for a security-related decision.

What is the severity of CWE-784?

CWE-784 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 5 real-world CVEs.