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Wiki MarkupAccording to the Java API \[[API 2006|AA. Bibliography#API 06]\], class {{SecurityManager}} documentationJava API Class SecurityManager documentation [API 2014],

The security manager is a class that allows applications to implement a security policy. It allows an application to determine, before performing a possibly unsafe or sensitive operation, what the operation is and whether it is being attempted in a security context that allows the operation to be performed. The application can allow or disallow the operation.

A security manager may be associated with any Java code.

The As an example, the applet security manager denies applets all but the most essential privileges. It is designed to protect against inadvertent system modification, information leakage, and user impersonation. The use of security managers is not limited to client-side protection. Webservers Web servers, such as Tomcat and Websphere WebSphere, use this facility to isolate trojan servlets , and malicious Java Server Pages (JSP) code and as well as to protect sensitive system resources from inadvertent access.

For Java applications that run from the command line , can set a default or custom security manager can be set using a special command-line flag. Alternatively, it is possible to install a security manager programaticallyprogrammatically. Installing a security manager this way programmatically helps create a default sandbox that allows or denies sensitive actions based on the basis of the security policy in effect.

From Java 2 SE Platform onwardsonward, SecurityManager is a non-abstract nonabstract class. As a result, there is no explicit requirement of overriding to override its methods. To create and use a security manager programaticallyprogrammatically, the code must have the runtime permissions createSecurityManager (to instantiate SecurityManager) and setSecurityManager (to install it). These permissions are checked only if a security manager is already installed. This is useful for situations where there is a global-in which a default security manager is in place, such as on a virtual host, and individual hosts need to must be denied the requisite permissions for overriding the default security manager with a custom one.

The security manager is closely tied to the AccessController class. The former is used as a hub for access control, whereas the latter is provides the actual implementer implementation of the access control algorithm. Two requirements necessitate the use of the The security manager :supports

• Providing backward compatibility: Legacy code often contains custom implementations of the security manager class because it was originally abstract.
• Defining custom policies: It is sometimes desired to subclass Subclassing the security manager to define permits definition of custom security policies (for example, multilevel, coarse, or fine grained security policies.

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• grain).

Regarding the implementation and use of custom security managers as opposed to default ones, the Java Security Architecture Specification \[[SecuritySpec 2008|AA. Bibliography#SecuritySpec 08]\] statesJava security architecture specification [SecuritySpec 2010] states:

We encourage the use of AccessController in application code, while customization of a security manager (via subclassing) should be the last resort and should be done with extreme care. Moreover, a customized security manager, such as one that always checks the time of the day before invoking standard security checks, could and should utilize the algorithm provided by AccessController whenever appropriate.

Many of the Java SE APIs use perform security manager checks by default before performing sensitive operations. For example, the constructor of class java.io.FileInputStream throws a SecurityException if the caller does not have the permission to read a file. Note that the documentation of some APIs, for example Because SecurityException is a subclass of RuntimeException, the declarations of some API methods (for example, those of the java.io.FileReader class, may not contain information about the SecurityException because it is a subclass of RuntimeException; it is not mandatory to document runtime exceptions) may lack a throws clause that lists the SecurityException. Avoid depending on the presence or absence of security manager checks that are not specified in the API method's documentation.

Noncompliant Code Example (Command-Line Installation)

This noncompliant code example does not fails to install the any security manager from the command line (assuming that the security manager is not set programatically). Consequently, the program runs with all permissions enabled; that is, there is no security manager to prevent any nefarious actions the program might perform.

java LocalJavaApp

Compliant Solution (Default Policy File)

Any Java program (bean, servlet or application) can instantiate a SecurityManager programatically in the absence of a default, global security manager that does not permit can attempt to install a SecurityManager programmatically, although the currently active security manager may forbid this operation. Applications designed to run locally can use specify a default global security manager by explicitly setting use of a flag on the command line while invoking the applicationat invocation.

The command-line option is usually preferred when applications must be prohibited from installing custom security managers programmatically , and are required to abide by the default global security policy under all circumstances. This compliant solution installs the default security manager using the appropriate command-line flags. The security policy file grants permissions to the application for allowable its intended actions.

java -Djava.security.manager -Djava.security.policy=policyURL \
     LocalJavaApp

Even The command-line flag can specify a custom security manager can be made the default and whose policies are enforced globally from the command line by specifying its absolute path location, immediately after an equal-to sign that must appear after the -. Use the -Djava.security.manager flag. If it is known in advance that the user prefers using the default global security manager installed from the command line, invoking the setSecurityManager() method can be forgone in code. In fact, using this method will throw a SecurityException if , as follows:

java -Djava.security.manager=my.security.CustomManager ...

If the current security policy enforced by the global current security manager does not permit forbids replacements (by not granting omitting the RuntimePermission("setSecurityManager")), any attempt to invoke setSecurityManager() will throw a SecurityException.

The default security policy file java.policy grants a few permissions (reading system properties, binding to unprivileged ports and so forth) and can be found in the ~—found in the /path/to/java.home/lib/security directory on UNIX-like systems and its equivalent on Microsoft Windows systems. There is also a user systems—grants a few permissions (reading system properties, binding to unprivileged ports, and so forth). A user-specific policy file may be located in the user's home directory. The union of both these policy files defines specifies the permissions given granted to a program. Refer to the The java.security file to set can specify which policy files should be are used. If either of these the systemwide java.policy or java.security files is deleted, by default no permissions are granted to the implementing codeexecuting Java program.

Compliant Solution (Custom Policy File)

If the default policy file needs to be bypassed in lieu of a custom policy file, the Use double equals (==) idiom should be used instead of the single equals =.(=) when overriding the global Java security policy file with a custom policy file:

java -Djava.security.manager \
     -Djava.security.policy==policyURL \
     LocalJavaApp

Compliant Solution (Additional Policy Files)

The appletviewer automatically installs a security manager with the standard policy file. To specify additional policy files, use the -J flag.

appletviewer -J-Djava.security.manager \
             -J-Djava.security.policy==policyURL LocalJavaApp

Wiki MarkupNotably, the policy file specified in the argument is ignored when the {{policy.allowSystemProperty}} property in the security properties file ({{java.security}}) is set to {{false}}. Its default value is {{true}}. The document "Default Policy Implementation and Policy File Syntax" \[[Policy 2002|AA. Bibliography#Policy 02]\] discusses writing policy files in depthNote that the policy file specified in the argument is ignored when the policy.allowSystemProperty property in the security properties file (java.security) is set to false; the default value of this property is true. Default Policy Implementation and Policy File Syntax [Policy 2010] discusses in depth the issues of and syntax for writing policy files.

Noncompliant Code Example (Programmatic Installation)

When the SecurityManager API is used to install the security manager instead of the command line, there can be instances where the appropriate checks are not installedA SecurityManager can also be activated using the static System.setSecurityManager() method. Only one SecurityManager may be active at a time. This method replaces the currently active SecurityManager with the SecurityManager provided in its argument or no SecurityManager if its argument is null.

This noncompliant code example passes a null value to the setSecurityManager method that is responsible for setting the expected SecurityManager argument. As a result, no security manager is installed (assuming that the security manager is not installed from the command line)deactivates any current SecurityManager but does not install another SecurityManager in its place. Consequently, subsequent code will run with all permissions enabled; there will be no restrictions on any nefarious action the program might perform.

try {
  System.setSecurityManager(null);
} catch (SecurityException se) {
  // cannotCannot set security manager, log to file
}

An active SecurityManager that enforces a sensible security policy will prevent the system from deactivating it, causing this code to throw a SecurityException.

Compliant Solution (Default Security Manager)

This compliant solution instantiates and sets the default security manager. :

try {
  System.setSecurityManager(new SecurityManager());
} catch (SecurityException se) {
  // cannotCannot set security manager, log to fileappropriately
}

Compliant Solution (Custom Security Manager)

This compliant solution demonstrates how to instantiate a custom SecurityManager class called CustomSecurityManager can be instantiated by invoking its constructor with a password, and set ; this custom security manager is then installed as the default active security manager.

char password[] = /* initialize */
try {
  System.setSecurityManager(
    new CustomSecurityManager("password here")
  );
} catch (SecurityException se) {
  // cannotCannot set security manager, log to fileappropriately
}

The After this code executes, APIs that have perform security checks built into them will use the custom security manager subsequently. As noted earlier, custom security managers should be installed only be rolled out when the default security manager does not provide lacks the required functionality.

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Applicability

Running Java code without a Security Manager being set means that there is no restrictive sandbox and arbitrary code may execute.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

\[[API 2006|AA. Bibliography#API 06]\] [Class SecurityManager|http://java.sun.com/javase/6/docs/api/java/lang/SecurityManager.html], Class AccessControlContext, Class AccessController
\[[Policy 2002|AA. Bibliography#Policy 02]\]
\[[Pistoia 2004|AA. Bibliography#Pistoia 04]\] Section 7.4, The Security Manager
\[[Gong 2003|AA. Bibliography#Gong 03]\] Section 6.1, Security Manager
\[[SecuritySpec 2008|AA. Bibliography#SecuritySpec 08]\] 6.2 SecurityManager versus AccessController
\[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE ID 358|http://cwe.mitre.org/data/definitions/358.html] "Improperly Implemented Security Check for Standard"

Java security fundamentally depends on the existence of a security manager. In its absence, sensitive actions can execute without restriction.

Programmatic detection of the presence or absence of a SecurityManager at runtime is straightforward. Static analysis can address the presence or absence of code that would attempt to install a SecurityManager if the code were executed. Checking whether the SecurityManager is installed early enough, whether it specifies the desired properties, or whether it is guaranteed to be installed may be possible in some special cases but is generally undecidable.

Bibliography

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Image Added Image Added Image AddedENV01-J. Place all privileged code in a single package and seal the package      01. Runtime Environment (ENV)      ENV03-J. Never grant AllPermission to untrusted code