Reliance on Cookies without Validation and Integrity Checking in a Security Decision
Draft Variant
Structure: Simple
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.
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
javaID : 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
phpThe 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
javaObserved 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
ID: REF-706
Writing Secure Code
Michael Howard and David LeBlanc
Microsoft Press
04-12-2002
ID: REF-7
Likelihood of Exploit
High
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Technologies:
Web Based : Often
Modes of Introduction
Implementation
Related Weaknesses
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.