CWE-271: Privilege Dropping / Lowering Errors

Description

The product does not drop privileges before passing control of a resource to an actor that does not have those privileges.

In some contexts, a system executing with elevated permissions will hand off a process/file/etc. to another process or user. If the privileges of an entity are not reduced, then elevated privileges are spread throughout a system and possibly to an attacker.

Potential Impact

Access Control

Gain Privileges or Assume Identity

Access Control, Non-Repudiation

Gain Privileges or Assume Identity, Hide Activities

Demonstrative Examples

The following code calls chroot() to restrict the application to a subset of the filesystem below APP_HOME in order to prevent an attacker from using the program to gain unauthorized access to files located elsewhere. The code then opens a file specified by the user and processes the contents of the file.

Bad

chroot(APP_HOME);chdir("/");FILE* data = fopen(argv[1], "r+");...

Constraining the process inside the application's home directory before opening any files is a valuable security measure. However, the absence of a call to setuid() with some non-zero value means the application is continuing to operate with unnecessary root privileges. Any successful exploit carried out by an attacker against the application can now result in a privilege escalation attack because any malicious operations will be performed with the privileges of the superuser. If the application drops to the privilege level of a non-root user, the potential for damage is substantially reduced.

Mitigations & Prevention

Architecture and Design

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

Architecture and DesignOperation

Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.

Architecture and Design

Consider following the principle of separation of privilege. Require multiple conditions to be met before permitting access to a system resource.

Real-World CVE Examples

CVE ID	Description
CVE-2000-1213	Program does not drop privileges after acquiring the raw socket.
CVE-2001-0559	Setuid program does not drop privileges after a parsing error occurs, then calls another program to handle the error.
CVE-2001-0787	Does not drop privileges in related groups when lowering privileges.
CVE-2002-0080	Does not drop privileges in related groups when lowering privileges.
CVE-2001-1029	Does not drop privileges before determining access to certain files.
CVE-1999-0813	Finger daemon does not drop privileges when executing programs on behalf of the user being fingered.
CVE-1999-1326	FTP server does not drop privileges if a connection is aborted during file transfer.
CVE-2000-0172	Program only uses seteuid to drop privileges.
CVE-2004-2504	Windows program running as SYSTEM does not drop privileges before executing other programs (many others like this, especially involving the Help facility).
CVE-2004-0213	Utility Manager launches winhlp32.exe while running with raised privileges, which allows local users to gain system privileges.
CVE-2004-0806	Setuid program does not drop privileges before executing program specified in an environment variable.
CVE-2004-0828	Setuid program does not drop privileges before processing file specified on command line.
CVE-2004-2070	Service on Windows does not drop privileges before using "view file" option, allowing code execution.

Taxonomy Mappings

PLOVER: — Privilege Dropping / Lowering Errors

Frequently Asked Questions

What is CWE-271?

CWE-271 (Privilege Dropping / Lowering Errors) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. The product does not drop privileges before passing control of a resource to an actor that does not have those privileges.

How can CWE-271 be exploited?

Attackers can exploit CWE-271 (Privilege Dropping / Lowering Errors) to gain privileges or assume identity. This weakness is typically introduced during the Architecture and Design, Implementation, Operation phase of software development.

How do I prevent CWE-271?

Key mitigations include: 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 interfaci

What is the severity of CWE-271?

CWE-271 is classified as a Class-level weakness (High abstraction). It has been observed in 13 real-world CVEs.