REALIZATION: This weakness is caused during implementation of an architectural security tactic.
Operation
N/A
Common Consequences
Impact: Gain Privileges or Assume Identity, Read Application Data, Read Files or Directories — Notes: An attacker may be able to access resources with the elevated privilege that could not be accessed with the attacker's original privileges. This is particularly likely in conjunction with another flaw, such as a buffer overflow.
Potential Mitigations
Architecture and Design: Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software. (N/A)
Architecture and Design: Follow the principle of least privilege when assigning access rights to entities in a software system. (N/A)
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 privilege to decide the appropriate time to use privileges and the time to drop privileges. (N/A)
Applicable Platforms
None (Not Language-Specific, Undetermined)
Demonstrative Examples
Intro: The following example demonstrates the weakness.
setuid(0); // Do some important stuff setuid(old_uid); // Do some non privileged stuff.
Intro: The following example demonstrates the weakness.
AccessController.doPrivileged(new PrivilegedAction() { public Object run() { // privileged code goes here, for example: System.loadLibrary("awt"); return null; // nothing to return }
Intro: 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.
Body: 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.
chroot(APP_HOME); chdir("/"); FILE* data = fopen(argv[1], "r+"); ...
Notes
Maintenance: CWE-271, CWE-272, and CWE-250 are all closely related and possibly overlapping. CWE-271 is probably better suited as a category.
Other: If system privileges are not dropped when it is reasonable to do so, this is not a vulnerability by itself. According to the principle of least privilege, access should be allowed only when it is absolutely necessary to the function of a given system, and only for the minimal necessary amount of time. Any further allowance of privilege widens the window of time during which a successful exploitation of the system will provide an attacker with that same privilege. If at all possible, limit the allowance of system privilege to small, simple sections of code that may be called atomically. When a program calls a privileged function, such as chroot(), it must first acquire root privilege. As soon as the privileged operation has completed, the program should drop root privilege and return to the privilege level of the invoking user.