CWE

Common Weakness Enumeration

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ID

CWE-749: Exposed Dangerous Method or Function

Weakness ID: 749
Abstraction: Base
Structure: Simple
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+ Description
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.
+ 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:

  • The function/method was never intended to be exposed to outside actors.
  • 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.
+ Relationships
Section HelpThis table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
+ Relevant to the view "Research Concepts" (CWE-1000)
NatureTypeIDName
ChildOfPillarPillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.284Improper Access Control
ParentOfVariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.618Exposed Unsafe ActiveX Method
ParentOfVariantVariant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.782Exposed IOCTL with Insufficient Access Control
Section HelpThis table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
+ Relevant to the view "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1228API / Function Errors
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
PhaseNote
Architecture and Design
Implementation
+ Applicable Platforms
Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

+ Common Consequences
Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
ScopeImpactLikelihood
Integrity
Confidentiality
Availability
Access Control
Other

Technical Impact: 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.
+ Likelihood Of Exploit
Low
+ 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 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();
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: 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:

  • 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)
+ Detection Methods

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Effectiveness: High

+ Memberships
Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.8082010 Top 25 - Weaknesses On the Cusp
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.975SFP Secondary Cluster: Architecture
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1416Comprehensive Categorization: Resource Lifecycle Management
+ Vulnerability Mapping Notes

Usage: Allowed

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use

Rationale:

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments:

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ Notes

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.
+ References
[REF-503] Microsoft. "Developing Secure ActiveX Controls". 2005-04-13. <https://learn.microsoft.com/en-us/previous-versions//ms533046(v=vs.85)?redirectedfrom=MSDN>. URL validated: 2023-04-07.
[REF-510] Microsoft. "How to stop an ActiveX control from running in Internet Explorer". <https://support.microsoft.com/en-us/help/240797/how-to-stop-an-activex-control-from-running-in-internet-explorer>. URL validated: 2023-04-07.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2008-11-24
(CWE 1.1, 2008-11-24)
CWE Content TeamMITRE
+ Modifications
Modification DateModifierOrganization
2009-01-12CWE Content TeamMITRE
updated Name
2009-07-27CWE Content TeamMITRE
updated Relationships
2009-12-28CWE Content TeamMITRE
updated Applicable_Platforms, Likelihood_of_Exploit
2010-02-16CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, Potential_Mitigations, References, Related_Attack_Patterns, Relationships
2010-04-05CWE Content TeamMITRE
updated Demonstrative_Examples, Related_Attack_Patterns
2010-06-21CWE Content TeamMITRE
updated Common_Consequences
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Relationships
2014-02-18CWE Content TeamMITRE
updated Demonstrative_Examples
2014-07-30CWE Content TeamMITRE
updated Relationships
2015-12-07CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Likelihood_of_Exploit, References, Relationships
2019-06-20CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Relationships
2023-01-31CWE Content TeamMITRE
updated Description, Related_Attack_Patterns, Relationships
2023-04-27CWE Content TeamMITRE
updated Detection_Factors, References, Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
+ Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Exposed Insecure Method or Function
Page Last Updated: October 26, 2023