Common Weakness Enumeration

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CWE-940: Improper Verification of Source of a Communication Channel

Weakness ID: 940
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software establishes a communication channel to handle an incoming request that has been initiated by an actor, but it does not properly verify that the request is coming from the expected origin.

Extended Description

When an attacker can successfully establish a communication channel from an untrusted origin, the attacker may be able to gain privileges and access unexpected functionality.

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



Architectural Paradigms

Mobile Application

+ Common Consequences
Access Control

Technical Impact: Gain privileges / assume identity; Varies by context

An attacker can access any functionality that is inadvertently accessible to the source.

+ Demonstrative Examples

Example 1

This Android application will remove a user account when it receives an intent to do so:

(Bad Code)
Example Language: Java 
IntentFilter filter = new IntentFilter("com.example.RemoveUser");
MyReceiver receiver = new MyReceiver();
registerReceiver(receiver, filter);

public class DeleteReceiver extends BroadcastReceiver {
public void onReceive(Context context, Intent intent) {
int userID = intent.getIntExtra("userID");

This application does not check the origin of the intent, thus allowing any malicious application to remove a user. Always check the origin of an intent, or create a whitelist of trusted applications using the manifest.xml file.

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

public boolean shouldOverrideUrlLoading(WebView view, String url){
if (url.substring(0,14).equalsIgnoreCase("examplescheme:")){
writeDataToView(view, UserData);
return false;
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:

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.

+ Observed Examples
DNS server can accept DNS updates from hosts that it did not query, leading to cache poisoning
DNS server can accept DNS updates from hosts that it did not query, leading to cache poisoning
DNS server caches glue records received from non-delegated name servers
+ Potential Mitigations

Phase: Architecture and Design

Use a mechanism that can validate the identity of the source, such as a certificate, and validate the integrity of data to ensure that it cannot be modified in transit using a man-in-the-middle attack.

When designing functionality of actions in the URL scheme, consider whether the action should be accessible to all mobile applications, or if a whitelist of applications to interface with is appropriate.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class923Improper Restriction of Communication Channel to Intended Endpoints
Development Concepts (primary)699
Research Concepts (primary)1000
+ Relationship Notes

While many access control issues involve authenticating the user, this weakness is more about authenticating the actual source of the communication channel itself; there might not be any "user" in such cases.

+ References
Taimur Aslam. "A Taxonomy of Security Faults in the UNIX Operating System". 1995-08-01. <>.
+ Content History
Submission DateSubmitterOrganizationSource
2014-02-13MITREInternal CWE Team

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Page Last Updated: May 05, 2017