COMMON WEAKNESS ENUMERATIONIncomplete

CWE-273

Improper Check for Dropped Privileges

The product attempts to drop privileges but does not check or incorrectly checks to see if the drop succeeded.

Abstraction

Base

Structure

Simple

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

The product attempts to drop privileges but does not check or incorrectly checks to see if the drop succeeded.

Extended description

If the drop fails, the product will continue to run with the raised privileges, which might provide additional access to unprivileged users.

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

REALIZATION: This weakness is caused during implementation of an architectural security tactic. This issue is likely to occur in restrictive environments in which the operating system or application provides fine-grained control over privilege management.
In Windows based environments that have access control, impersonation is used so that access checks can be performed on a client identity by a server with higher privileges. By impersonating the client, the server is restricted to client-level security -- although in different threads it may have much higher privileges.

Risk

What does successful exploitation lead to?

Gain Privileges or Assume Identity

Affected security scopes: Access Control

If privileges are not dropped, neither are access rights of the user. Often these rights can be prevented from being dropped.
Gain Privileges or Assume IdentityHide Activities

Affected security scopes: Access Control, Non-Repudiation

If privileges are not dropped, in some cases the system may record actions as the user which is being impersonated rather than the impersonator.

Defence

How is it prevented and fixed?

Architecture and Design

Separation of Privilege

Detail
Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

Implementation

Implementation-phase defence

Detail
Check the results of all functions that return a value and verify that the value is expected.

Effectiveness: High

Checking the return value of the function will typically be sufficient, however beware of race conditions (CWE-362) in a concurrent environment.

Implementation

Implementation-phase defence

Detail
In Windows, make sure that the process token has the SeImpersonatePrivilege(Microsoft Server 2003). Code that relies on impersonation for security must ensure that the impersonation succeeded, i.e., that a proper privilege demotion happened.

Verification

How is it detected?

Automated Static Analysis

High
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)