Optimize the document of Quark Script CWE-940

[JerryTasi]

Detect CWE-940 in Android Application

This scenario seeks to find the Improper Verification of Source of a Communication Channel in the APK file.

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

We analyze the definition of CWE-940 and identify its characteristics.

See CWE-940 for more details.

Code of CWE-940 in ovaa.apk

We use the ovaa.apk sample to explain the vulnerability code of CWE-940.

Quark Script: CWE-940.py

Let’s use the above APIs to show how the Quark script finds this vulnerability.

To begin with, we create a detection rule named LoadUrlFromIntent.json to identify behavior that loads URLs from intent data to the WebView.

Next, we retrieve the methods that pass the URL. Then, we check if these methods are only for getting the URL, such as findViewById, getStringExtra, or getIntent.

If YES, it could imply that the APK uses communication channels without proper verification, which may cause CWE-940 vulnerability.

from quark.script import runQuarkAnalysis, Rule

SAMPLE_PATH = "ovaa.apk"
RULE_PATH = "LoadUrlFromIntent.json"

URL_GETTING_METHODS = [
    "findViewById",
    "getStringExtra",
    "getIntent",
]

ruleInstance = Rule(RULE_PATH)

quarkResult = runQuarkAnalysis(SAMPLE_PATH, ruleInstance)

for behaviorInstance in quarkResult.behaviorOccurList:
    methodsInArgs = behaviorInstance.getMethodsInArgs()

    verifiedMethodCandidates = []

    for method in methodsInArgs:
        if method.methodName not in URL_GETTING_METHODS:
            verifiedMethodCandidates.append(method)

    if verifiedMethodCandidates == []:
        caller = behaviorInstance.methodCaller.fullName
        print(f"CWE-940 is detected in method, {caller}")

Quark Rule: LoadUrlFromIntent.json

{
    "crime": "Load Url from Intent",
    "permission": [],
    "api": [
        {
            "class": "Landroid/content/Intent;",
            "method": "getStringExtra",
            "descriptor": "(Ljava/lang/String;)Ljava/lang/String"
        },
        {
            "class": "Landroid/webkit/WebView;",
            "method": "loadUrl",
            "descriptor": "(Ljava/lang/String;)V"
        }
    ],
    "score": 1,
    "label": []
}

Quark Script Result

$ python CWE-940.py
CWE-940 is detected in method, Loversecured/ovaa/activities/WebViewActivity; onCreate (Landroid/os/Bundle;)V