Process Control

Executing commands or loading libraries from an untrusted source or in an untrusted environment can cause an application to execute malicious commands (and payloads) on behalf of an attacker.


Description

Process control vulnerabilities take two forms: 1. An attacker can change the command that the program executes: the attacker explicitly controls what the command is. 2. An attacker can change the environment in which the command executes: the attacker implicitly controls what the command means. Process control vulnerabilities of the first type occur when either data enters the application from an untrusted source and the data is used as part of a string representing a command that is executed by the application. By executing the command, the application gives an attacker a privilege or capability that the attacker would not otherwise have.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following code uses System.loadLibrary() to load code from a native library named library.dll, which is normally found in a standard system directory.

...
System.loadLibrary("library.dll");
...

The problem here is that System.loadLibrary() accepts a library name, not a path, for the library to be loaded. From the Java 1.4.2 API documentation this function behaves as follows [1]: A file containing native code is loaded from the local file system from a place where library files are conventionally obtained. The details of this process are implementation-dependent. The mapping from a library name to a specific filename is done in a system-specific manner. If an attacker is able to place a malicious copy of library.dll higher in the search order than file the application intends to load, then the application will load the malicious copy instead of the intended file. Because of the nature of the application, it runs with elevated privileges, which means the contents of the attacker's library.dll will now be run with elevated privileges, possibly giving them complete control of the system.

Example Two

The following code from a privileged application uses a registry entry to determine the directory in which it is installed and loads a library file based on a relative path from the specified directory.

...
RegQueryValueEx(hkey, "APPHOME",
0, 0, (BYTE*)home, &size);
char* lib=(char*)malloc(strlen(home)+strlen(INITLIB));
if (lib) {


  strcpy(lib,home);
  strcat(lib,INITCMD);
  LoadLibrary(lib);

}
...

The code in this example allows an attacker to load an arbitrary library, from which code will be executed with the elevated privilege of the application, by modifying a registry key to specify a different path containing a malicious version of INITLIB. Because the program does not validate the value read from the environment, if an attacker can control the value of APPHOME, they can fool the application into running malicious code.

Example Three

The following code is from a web-based administration utility that allows users access to an interface through which they can update their profile on the system. The utility makes use of a library named liberty.dll, which is normally found in a standard system directory.

LoadLibrary("liberty.dll");

The problem is that the program does not specify an absolute path for liberty.dll. If an attacker is able to place a malicious library named liberty.dll higher in the search order than file the application intends to load, then the application will load the malicious copy instead of the intended file. Because of the nature of the application, it runs with elevated privileges, which means the contents of the attacker's liberty.dll will now be run with elevated privileges, possibly giving the attacker complete control of the system. The type of attack seen in this example is made possible because of the search order used by LoadLibrary() when an absolute path is not specified. If the current directory is searched before system directories, as was the case up until the most recent versions of Windows, then this type of attack becomes trivial if the attacker can execute the program locally. The search order is operating system version dependent, and is controlled on newer operating systems by the value of the registry key: HKLM\System\CurrentControlSet\Control\Session Manager\SafeDllSearchMode

See Also

Authorize Actors

Weaknesses in this category are related to the design and architecture of a system's authorization components. Frequently these deal with enforcing that agents have th...

SFP Secondary Cluster: Tainted Input to Environment

This category identifies Software Fault Patterns (SFPs) within the Tainted Input to Environment cluster (SFP27).

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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