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Merge pull request #14752 from masterofnow/LoadClassNoSignatureCheck
Java: Insecure Loading of Class in Android App without Package Signature Checking
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‎java/ql/src/experimental/Security/CWE/CWE-470/BadClassLoader.java

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package poc.sample.classloader;
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import android.app.Application;
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import android.content.pm.PackageInfo;
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import android.content.Context;
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import android.util.Log;
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public class BadClassLoader extends Application {
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@Override
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public void onCreate() {
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super.onCreate();
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for (PackageInfo p : getPackageManager().getInstalledPackages(0)) {
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try {
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if (p.packageName.startsWith("some.package.")) {
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Context appContext = createPackageContext(p.packageName,
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CONTEXT_INCLUDE_CODE | CONTEXT_IGNORE_SECURITY);
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ClassLoader classLoader = appContext.getClassLoader();
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Object result = classLoader.loadClass("some.package.SomeClass")
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.getMethod("someMethod")
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.invoke(null);
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}
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} catch (Exception e) {
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Log.e("Class loading failed", e.toString());
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}
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}
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}
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}

‎java/ql/src/experimental/Security/CWE/CWE-470/GoodClassLoader.java

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package poc.sample.classloader;
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import android.app.Application;
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import android.content.pm.PackageInfo;
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import android.content.Context;
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import android.content.pm.PackageManager;
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import android.util.Log;
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public class GoodClassLoader extends Application {
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@Override
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public void onCreate() {
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super.onCreate();
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PackageManager pm = getPackageManager();
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for (PackageInfo p : pm.getInstalledPackages(0)) {
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try {
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if (p.packageName.startsWith("some.package.") &&
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(pm.checkSignatures(p.packageName, getApplicationContext().getPackageName()) == PackageManager.SIGNATURE_MATCH)
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) {
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Context appContext = createPackageContext(p.packageName,
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CONTEXT_INCLUDE_CODE | CONTEXT_IGNORE_SECURITY);
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ClassLoader classLoader = appContext.getClassLoader();
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Object result = classLoader.loadClass("some.package.SomeClass")
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.getMethod("someMethod")
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.invoke(null);
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}
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} catch (Exception e) {
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Log.e("Class loading failed", e.toString());
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}
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}
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}
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}

‎java/ql/src/experimental/Security/CWE/CWE-470/LoadClassNoSignatureCheck.qhelp

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<!DOCTYPE qhelp PUBLIC "-//Semmle//qhelp//EN" "qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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If an application loads classes or code from another app based solely on its package name without
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first checking its package signature, this could allow a malicious app with the same package name
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to be loaded through "package namespace squatting".
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If the victim user install such malicious app in the same device as the vulnerable app, the vulnerable app would load
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classes or code from the malicious app, potentially leading to arbitrary code execution.
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</p>
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</overview>
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<recommendation>
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<p>
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Verify the package signature in addition to the package name before loading any classes or code from another application.
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</p>
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</recommendation>
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<example>
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<p>
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The <code>BadClassLoader</code> class illustrates class loading with the <code>android.content.pm.PackageInfo.packageName.startsWith()</code> method without any check on the package signature.
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</p>
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<sample src="BadClassLoader.java" />
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<p>
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The <code>GoodClassLoader</code> class illustrates class loading with correct package signature check using the <code>android.content.pm.PackageManager.checkSignatures()</code> method.
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</p>
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<sample src="GoodClassLoader.java" />
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</example>
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<references>
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<li>
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<a href="https://blog.oversecured.com/Android-arbitrary-code-execution-via-third-party-package-contexts/">
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Oversecured (Android: arbitrary code execution via third-party package contexts)
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</a>
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</li>
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</references>
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</qhelp>

‎java/ql/src/experimental/Security/CWE/CWE-470/LoadClassNoSignatureCheck.ql

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/**
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* @name Load 3rd party classes or code ('unsafe reflection') without signature check
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* @description Loading classes or code from third-party packages without checking the
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* package signature could make the application
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* susceptible to package namespace squatting attacks,
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* potentially leading to arbitrary code execution.
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* @problem.severity error
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* @precision high
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* @kind path-problem
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* @id java/android/unsafe-reflection
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* @tags security
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* experimental
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* external/cwe/cwe-470
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*/
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import java
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import semmle.code.java.dataflow.TaintTracking
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import semmle.code.java.controlflow.Guards
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import semmle.code.java.dataflow.SSA
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import semmle.code.java.frameworks.android.Intent
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class CheckSignaturesGuard extends Guard instanceof EqualityTest {
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MethodCall checkSignatures;
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CheckSignaturesGuard() {
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this.getAnOperand() = checkSignatures and
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checkSignatures
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.getMethod()
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.hasQualifiedName("android.content.pm", "PackageManager", "checkSignatures") and
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exists(Expr signatureCheckResult |
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this.getAnOperand() = signatureCheckResult and signatureCheckResult != checkSignatures
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|
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signatureCheckResult.(CompileTimeConstantExpr).getIntValue() = 0 or
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signatureCheckResult
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.(FieldRead)
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.getField()
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.hasQualifiedName("android.content.pm", "PackageManager", "SIGNATURE_MATCH")
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)
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}
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Expr getCheckedExpr() { result = checkSignatures.getArgument(0) }
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}
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predicate signatureChecked(Expr safe) {
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exists(CheckSignaturesGuard g, SsaVariable v |
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v.getAUse() = g.getCheckedExpr() and
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safe = v.getAUse() and
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g.controls(safe.getBasicBlock(), g.(EqualityTest).polarity())
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)
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}
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module InsecureLoadingConfig implements DataFlow::ConfigSig {
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predicate isSource(DataFlow::Node src) {
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exists(Method m | m = src.asExpr().(MethodCall).getMethod() |
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m.getDeclaringType().getASourceSupertype*() instanceof TypeContext and
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m.hasName("createPackageContext") and
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not signatureChecked(src.asExpr().(MethodCall).getArgument(0))
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)
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}
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predicate isSink(DataFlow::Node sink) {
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exists(MethodCall ma |
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ma.getMethod().hasQualifiedName("java.lang", "ClassLoader", "loadClass")
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|
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sink.asExpr() = ma.getQualifier()
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)
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}
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predicate isAdditionalFlowStep(DataFlow::Node node1, DataFlow::Node node2) {
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exists(MethodCall ma, Method m |
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ma.getMethod() = m and
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m.getDeclaringType().getASourceSupertype*() instanceof TypeContext and
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m.hasName("getClassLoader")
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|
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node1.asExpr() = ma.getQualifier() and
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node2.asExpr() = ma
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)
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}
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}
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module InsecureLoadFlow = TaintTracking::Global<InsecureLoadingConfig>;
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import InsecureLoadFlow::PathGraph
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from InsecureLoadFlow::PathNode source, InsecureLoadFlow::PathNode sink
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where InsecureLoadFlow::flowPath(source, sink)
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select sink.getNode(), source, sink, "Class loaded from a $@ without signature check",
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source.getNode(), "third party library"

‎java/ql/test/experimental/query-tests/security/CWE-470/BadClassLoader.java

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package poc.sample.classloader;
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import android.app.Application;
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import android.content.pm.PackageInfo;
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import android.content.Context;
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import android.util.Log;
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public class BadClassLoader extends Application {
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@Override
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public void onCreate() {
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super.onCreate();
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for (PackageInfo p : getPackageManager().getInstalledPackages(0)) {
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try {
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if (p.packageName.startsWith("some.package.")) {
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Context appContext = createPackageContext(p.packageName,
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CONTEXT_INCLUDE_CODE | CONTEXT_IGNORE_SECURITY);
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ClassLoader classLoader = appContext.getClassLoader();
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Object result = classLoader.loadClass("some.package.SomeClass")
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.getMethod("someMethod")
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.invoke(null);
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}
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} catch (Exception e) {
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Log.e("Class loading failed", e.toString());
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}
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}
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}
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}

‎java/ql/test/experimental/query-tests/security/CWE-470/GoodClassLoader.java

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package poc.sample.classloader;
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import android.app.Application;
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import android.content.pm.PackageInfo;
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import android.content.Context;
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import android.content.pm.PackageManager;
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import android.util.Log;
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public class GoodClassLoader extends Application {
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@Override
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public void onCreate() {
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super.onCreate();
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PackageManager pm = getPackageManager();
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for (PackageInfo p : pm.getInstalledPackages(0)) {
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try {
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if (p.packageName.startsWith("some.package.") &&
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(pm.checkSignatures(p.packageName, getApplicationContext().getPackageName()) == PackageManager.SIGNATURE_MATCH)
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) {
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Context appContext = createPackageContext(p.packageName,
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CONTEXT_INCLUDE_CODE | CONTEXT_IGNORE_SECURITY);
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ClassLoader classLoader = appContext.getClassLoader();
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Object result = classLoader.loadClass("some.package.SomeClass")
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.getMethod("someMethod")
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.invoke(null);
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}
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} catch (Exception e) {
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Log.e("Class loading failed", e.toString());
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}
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}
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}
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}

‎java/ql/test/experimental/query-tests/security/CWE-470/LoadClassNoSignatureCheck.expected

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edges
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| BadClassLoader.java:15:42:16:75 | createPackageContext(...) : Context | BadClassLoader.java:17:47:17:56 | appContext : Context |
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| BadClassLoader.java:17:47:17:56 | appContext : Context | BadClassLoader.java:17:47:17:73 | getClassLoader(...) : ClassLoader |
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| BadClassLoader.java:17:47:17:73 | getClassLoader(...) : ClassLoader | BadClassLoader.java:18:37:18:47 | classLoader |
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nodes
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| BadClassLoader.java:15:42:16:75 | createPackageContext(...) : Context | semmle.label | createPackageContext(...) : Context |
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| BadClassLoader.java:17:47:17:56 | appContext : Context | semmle.label | appContext : Context |
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| BadClassLoader.java:17:47:17:73 | getClassLoader(...) : ClassLoader | semmle.label | getClassLoader(...) : ClassLoader |
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| BadClassLoader.java:18:37:18:47 | classLoader | semmle.label | classLoader |
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subpaths
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#select
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| BadClassLoader.java:18:37:18:47 | classLoader | BadClassLoader.java:15:42:16:75 | createPackageContext(...) : Context | BadClassLoader.java:18:37:18:47 | classLoader | Class loaded from a $@ without signature check | BadClassLoader.java:15:42:16:75 | createPackageContext(...) | third party library |

‎java/ql/test/experimental/query-tests/security/CWE-470/LoadClassNoSignatureCheck.qlref

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experimental/Security/CWE/CWE-470/LoadClassNoSignatureCheck.ql

‎java/ql/test/experimental/query-tests/security/CWE-470/options

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//semmle-extractor-options: --javac-args -cp ${testdir}/../../../../stubs/servlet-api-2.4:${testdir}/../../../../stubs/springframework-5.3.8/
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//semmle-extractor-options: --javac-args -cp ${testdir}/../../../../stubs/servlet-api-2.4:${testdir}/../../../../stubs/springframework-5.3.8/:${testdir}/../../../../stubs/google-android-9.0.0

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