Common Weakness Enumeration

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

Weakness ID: 940
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
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.
+ Relationships

The table(s) below 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)
+ Relevant to the view "Architectural Concepts" (CWE-1008)
MemberOfCategoryCategory1014Identify Actors
+ Relevant to the view "Development Concepts" (CWE-699)
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
ImplementationREALIZATION: This weakness is caused during implementation of an architectural security tactic.
+ Applicable Platforms
The listings below show 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.


Class: Language-Independent (Undetermined Prevalence)


Mobile (Undetermined Prevalence)

+ Common Consequences

The table below 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.

Access Control

Technical Impact: Gain Privileges or 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:

(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.

+ 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.

+ 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
[REF-324] Taimur Aslam. "A Taxonomy of Security Faults in the UNIX Operating System". 1995-08-01. <>.
+ Content History
Submission DateSubmitterOrganization
2014-02-13CWE Content TeamMITRE
Modification DateModifierOrganization
2017-11-08CWE Content TeamMITRE
updated Modes_of_Introduction, References, Relationships

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Page Last Updated: January 18, 2018