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Reliance on Cookies without Validation and Integrity Checking in a Security Decision

Draft Variant
Structure: Simple
Description

This vulnerability occurs when an application makes security decisions—like granting access or verifying identity—based solely on cookie data without first confirming the cookie's authenticity or integrity.

Extended Description

Attackers can easily manipulate cookie values directly in the browser or by crafting custom client-side requests. Since the application trusts this data without validation, attackers can forge cookies to impersonate other users, bypass login screens, or escalate their privileges by inserting expected values. To prevent this, developers must never treat cookies as a trusted security mechanism on their own. Always validate and verify cookie integrity on the server using techniques like cryptographic signing, comparing against server-side sessions, or using secure, tamper-proof tokens instead of plain data.
Common Consequences 1
Scope: Access Control

Impact: Bypass Protection MechanismGain 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.
Potential Mitigations 4
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.
Demonstrative Examples 3

ID : DX-15

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

Code Example:

Bad
Java
java

ID : DX-16

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

Code Example:

Bad
PHP
php
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.

ID : DX-17

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

Code Example:

Bad
Java
java
Observed Examples 5
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."
References 2
Unforgivable Vulnerabilities
Steve Christey
02-08-2007
http://cve.mitre.org/docs/docs-2007/unforgivable.pdf
ID: REF-706
Writing Secure Code
Michael Howard and David LeBlanc
Microsoft Press
04-12-2002
https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223
ID: REF-7
Likelihood of Exploit

High

Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Technologies:
Web Based : Often
Modes of Introduction
Implementation
Related Weaknesses
ChildOf: Reliance on Untrusted Inputs in a Security Decision (CWE-807)
ChildOf: Reliance on Cookies without Validation and Integrity Checking (CWE-565)
Notes
MaintenanceA 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 DEPRECATED: Reliance on DNS Lookups in a Security Decision and External Control of Assumed-Immutable Web Parameter.