CWE-749 暴露危险的方法或函数

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所属分类:CWE(弱点枚举)

CWE-749 暴露危险的方法或函数

Exposed Dangerous Method or Function

结构: Simple

Abstraction: Base

状态: Incomplete

被利用可能性: Low

基本描述

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.

扩展描述

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:

相关缺陷

  • cwe_Nature: ChildOf cwe_CWE_ID: 664 cwe_View_ID: 1000 cwe_Ordinal: Primary

  • cwe_Nature: ChildOf cwe_CWE_ID: 691 cwe_View_ID: 1000

适用平台

Language: {'cwe_Class': 'Language-Independent', 'cwe_Prevalence': 'Undetermined'}

常见的影响

范围 影响 注释
['Integrity', 'Confidentiality', 'Availability', 'Access Control', 'Other'] ['Gain Privileges or 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.

可能的缓解方案

Architecture and Design

策略:

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.

['Architecture and Design', 'Implementation']

策略: Attack Surface Reduction

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

示例代码

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

bad 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 Java

private void removeDatabase(String databaseName) {

try {

Statement stmt = conn.createStatement();
stmt.execute("DROP DATABASE " + databaseName);

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

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 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 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 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.

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 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 JavaScript

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