Improper Check for Dropped Privileges

Description

This vulnerability occurs when an application tries to lower its system privileges but fails to verify that the operation was successful.

Extended Description

When a program temporarily elevates its permissions to perform a sensitive task, it should reliably revert to a less-privileged state afterward. If the code doesn't properly confirm this privilege drop—perhaps due to a missing error check or a flawed verification logic—the application continues running with its elevated access rights. This creates a critical security gap, as an attacker could potentially exploit the retained high privileges to perform unauthorized actions, access restricted data, or modify system settings. Essentially, the intended security boundary fails, leaving the system exposed to the very risks the privilege drop was meant to prevent.

Common Consequences 2

Scope: Access Control

Impact: Gain Privileges or Assume Identity

If privileges are not dropped, neither are access rights of the user. Often these rights can be prevented from being dropped.

Scope: Access ControlNon-Repudiation

Impact: Gain Privileges or Assume IdentityHide Activities

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

Detection Methods 1

Automated Static AnalysisHigh

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.)

Potential Mitigations 3

Phase: Architecture and Design

Strategy: Separation of Privilege

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.

Phase: Implementation

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

Effectiveness: High

Phase: Implementation

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.

Demonstrative Examples 1

This code attempts to take on the privileges of a user before creating a file, thus avoiding performing the action with unnecessarily high privileges:

Code Example:Bad
C++
c++

The call to ImpersonateNamedPipeClient may fail, but the return value is not checked. If the call fails, the code may execute with higher privileges than intended. In this case, an attacker could exploit this behavior to write a file to a location that the attacker does not have access to.

Observed Examples 2

CVE-2006-4447Program does not check return value when invoking functions to drop privileges, which could leave users with higher privileges than expected by forcing those functions to fail.

CVE-2006-2916Program does not check return value when invoking functions to drop privileges, which could leave users with higher privileges than expected by forcing those functions to fail.

References 1

The CLASP Application Security Process

Secure Software, Inc.

2005

https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)

ID: REF-18

Likelihood of Exploit

Medium

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction