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Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

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ID

CWE-749: Exposed Dangerous Method or Function

Weakness ID: 749
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.

Extended Description

This weakness can lead to a wide variety of resultant weaknesses, depending on the behavior of the exposed method. It can apply to any number of technologies and approaches, such as ActiveX controls, Java functions, IOCTLs, and so on.

The exposure can occur in a few different ways:

1) The function/method was never intended to be exposed to outside actors.

2) The function/method was only intended to be accessible to a limited set of actors, such as Internet-based access from a single web site.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

Language-independent

+ Common Consequences
ScopeEffect
Integrity
Confidentiality
Availability
Access Control
Other

Technical Impact: Gain privileges / assume identity; Read application data; Modify application data; Execute unauthorized code or commands; Other

Exposing critical functionality essentially provides an attacker with the privilege level of the exposed functionality. This could result in the modification or exposure of sensitive data or possibly even execution of arbitrary code.

+ Likelihood of Exploit

Low to Medium

+ Demonstrative Examples

Example 1

In the following Java example the method removeDatabase will delete the database with the name specified in the input parameter.

(Bad Code)
Example Language: Java 
public void removeDatabase(String databaseName) {
try {
Statement stmt = conn.createStatement();
stmt.execute("DROP DATABASE " + databaseName);

} catch (SQLException ex) {...}
}

The method in this example is declared public and therefore is exposed to any class in the application. Deleting a database should be considered a critical operation within an application and access to this potentially dangerous method should be restricted. Within Java this can be accomplished simply by declaring the method private thereby exposing it only to the enclosing class as in the following example.

(Good Code)
Example Language: Java 
private void removeDatabase(String databaseName) {
try {
Statement stmt = conn.createStatement();
stmt.execute("DROP DATABASE " + databaseName);

} catch (SQLException ex) {...}
}

Example 2

These Android and iOS applications intercept URL loading within a WebView and perform special actions if a particular URL scheme is used, thus allowing the Javascript within the WebView to communicate with the application:

(Bad Code)
Example Language: Java 
// Android

@Override
public boolean shouldOverrideUrlLoading(WebView view, String url){
if (url.substring(0,14).equalsIgnoreCase("examplescheme:")){
if(url.substring(14,25).equalsIgnoreCase("getUserInfo")){
writeDataToView(view, UserData);
return false;
}
else{
return true;
}
}
}
(Bad Code)
Example Language: Objective-C 
// iOS

-(BOOL) webView:(UIWebView *)exWebView shouldStartLoadWithRequest:(NSURLRequest *)exRequest navigationType:(UIWebViewNavigationType)exNavigationType
{
NSURL *URL = [exRequest URL];
if ([[URL scheme] isEqualToString:@"exampleScheme"])
{
NSString *functionString = [URL resourceSpecifier];
if ([functionString hasPrefix:@"specialFunction"])
{
// Make data available back in webview.
UIWebView *webView = [self writeDataToView:[URL query]];
}
return NO;
}
return YES;
}

A call into native code can then be initiated by passing parameters within the URL:

(Attack)
Example Language: Javascript 
window.location = examplescheme://method?parameter=value

Because the application does not check the source, a malicious website loaded within this WebView has the same access to the API as a trusted site.

Example 3

This application uses a WebView to display websites, and creates a Javascript interface to a Java object to allow enhanced functionality on a trusted website:

(Bad Code)
Example Language: Java 
public class WebViewGUI extends Activity {
WebView mainWebView;

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mainWebView = new WebView(this);
mainWebView.getSettings().setJavaScriptEnabled(true);
mainWebView.addJavascriptInterface(new JavaScriptInterface(), "userInfoObject");
mainWebView.loadUrl("file:///android_asset/www/index.html");
setContentView(mainWebView);
}

final class JavaScriptInterface {
JavaScriptInterface () {}

public String getUserInfo() {
return currentUser.Info();
}
}
}

Before Android 4.2 all methods, including inherited ones, are exposed to Javascript when using addJavascriptInterface(). This means that a malicious website loaded within this WebView can use reflection to acquire a reference to arbitrary Java objects. This will allow the website code to perform any action the parent application is authorized to.

For example, if the application has permission to send text messages:

(Attack)
Example Language: Javascript 
<script>
userInfoObject.getClass().forName('android.telephony.SmsManager').getMethod('getDefault',null).sendTextMessage(attackNumber, null, attackMessage, null, null);
</script>

This malicious script can use the userInfoObject object to load the SmsManager object and send arbitrary text messages to any recipient.

Example 4

After Android 4.2, only methods annotated with @JavascriptInterface are available in JavaScript, protecting usage of getClass() by default, as in this example:

(Bad Code)
Example Language: Java 
final class JavaScriptInterface {
JavaScriptInterface () { }

@JavascriptInterface
public String getUserInfo() {
return currentUser.Info();
}
}

This code is not vulnerable to the above attack, but still may expose user info to malicious pages loaded in the WebView. Even malicious iframes loaded within a trusted page may access the exposed interface:

(Attack)
Example Language: Javascript 
<script>
var info = window.userInfoObject.getUserInfo();
sendUserInfo(info);
</script>

This malicious code within an iframe is able to access the interface object and steal the user's data.

+ Observed Examples
ReferenceDescription
arbitrary Java code execution via exposed method
security tool ActiveX control allows download or upload of files
+ Potential Mitigations

Phase: Architecture and Design

If you must expose a method, make sure to perform input validation on all arguments, limit access to authorized parties, and protect against all possible vulnerabilities.

Phases: Architecture and Design; Implementation

Strategy: Identify and Reduce Attack Surface

Identify all exposed functionality. Explicitly list all functionality that must be exposed to some user or set of users. Identify which functionality may be:

  • accessible to all users

  • restricted to a small set of privileged users

  • prevented from being directly accessible at all

Ensure that the implemented code follows these expectations. This includes setting the appropriate access modifiers where applicable (public, private, protected, etc.) or not marking ActiveX controls safe-for-scripting.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class485Insufficient Encapsulation
Development Concepts (primary)699
Research Concepts (primary)1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfWeakness ClassWeakness Class691Insufficient Control Flow Management
Research Concepts1000
ChildOfCategoryCategory8082010 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory975SFP Secondary Cluster: Architecture
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base618Exposed Unsafe ActiveX Method
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant782Exposed IOCTL with Insufficient Access Control
Development Concepts (primary)699
Research Concepts (primary)1000
+ Research Gaps

Under-reported and under-studied. This weakness could appear in any technology, language, or framework that allows the programmer to provide a functional interface to external parties, but it is not heavily reported. In 2007, CVE began showing a notable increase in reports of exposed method vulnerabilities in ActiveX applications, as well as IOCTL access to OS-level resources. These weaknesses have been documented for Java applications in various secure programming sources, but there are few reports in CVE, which suggests limited awareness in most parts of the vulnerability research community.

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
2008-11-24Internal CWE Team
Modifications
Modification DateModifierOrganizationSource
2009-01-12CWE Content TeamMITREInternal
updated Name
2009-07-27CWE Content TeamMITREInternal
updated Relationships
2009-12-28CWE Content TeamMITREInternal
updated Applicable_Platforms, Likelihood_of_Exploit
2010-02-16CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Potential_Mitigations, References, Related_Attack_Patterns, Relationships
2010-04-05CWE Content TeamMITREInternal
updated Demonstrative_Examples, Related_Attack_Patterns
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Relationships
2014-02-18CWE Content TeamMITREInternal
updated Demonstrative_Examples
2014-07-30CWE Content TeamMITREInternal
updated Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Exposed Insecure Method or Function

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Page Last Updated: January 18, 2017