CWE-749: Exposed Dangerous Method or Function
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The product 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. 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:
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![]() Languages Class: Not Language-Specific (Undetermined Prevalence) ![]()
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); 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); } 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 code) 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 code) 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 code) Example Language: JavaScript <script>
var info = window.userInfoObject.getUserInfo(); </script>sendUserInfo(info); This malicious code within an iframe is able to access the interface object and steal the user's data.
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Research Gap 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.
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