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Add Fragment injection query
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‎java/ql/lib/semmle/code/java/frameworks/android/Fragment.qll

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import java
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/** The class `android.app.Fragment` */
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class Fragment extends Class {
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Fragment() { this.hasQualifiedName("android.app", "Fragment") }
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}
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/** The method `instantiate` of the class `android.app.Fragment`. */
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class FragmentInstantiateMethod extends Method {
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FragmentInstantiateMethod() {
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this.getDeclaringType() instanceof Fragment and
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this.hasName("instantiate")
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}
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}

‎java/ql/lib/semmle/code/java/security/FragmentInjection.qll

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import java
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private import semmle.code.java.dataflow.TaintTracking
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private import semmle.code.java.dataflow.ExternalFlow
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private import semmle.code.java.frameworks.android.Android
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private import semmle.code.java.frameworks.android.Fragment
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private import semmle.code.java.Reflection
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/**
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* A sink for Fragment injection vulnerabilities,
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* that is, method calls that dynamically add Fragments to Activities.
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*/
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abstract class FragmentInjectionSink extends DataFlow::Node { }
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/**
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* A unit class for adding additional taint steps.
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*
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* Extend this class to add additional taint steps that should apply to `FragmentInjectionTaintConf`.
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*/
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class FragmentInjectionAdditionalTaintStep extends Unit {
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abstract predicate step(DataFlow::Node n1, DataFlow::Node n2);
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}
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private class FragmentInjectionSinkModels extends SinkModelCsv {
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override predicate row(string row) {
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row =
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["android.app", "android.support.v4.app", "androidx.fragment.app"] +
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";FragmentTransaction;true;" +
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[
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"add;(Class,Bundle,String);;Argument[0]", "add;(Fragment,String);;Argument[0]",
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"add;(int,Class,Bundle);;Argument[1]", "add;(int,Fragment);;Argument[1]",
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"add;(int,Class,Bundle,String);;Argument[1]", "add;(int,Fragment,String);;Argument[1]",
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"attach;(Fragment);;Argument[0]", "replace;(int,Class,Bundle);;Argument[1]",
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"replace;(int,Fragment);;Argument[1]", "replace;(int,Class,Bundle,String);;Argument[1]",
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"replace;(int,Fragment,String);;Argument[1]",
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] + ";fragment-injection"
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}
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}
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private class DefaultFragmentInjectionSink extends FragmentInjectionSink {
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DefaultFragmentInjectionSink() { sinkNode(this, "fragment-injection") }
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}
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private class DefaultFragmentInjectionAdditionalTaintStep extends FragmentInjectionAdditionalTaintStep {
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override predicate step(DataFlow::Node n1, DataFlow::Node n2) {
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exists(ReflectiveClassIdentifierMethodAccess ma |
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ma.getArgument(0) = n1.asExpr() and ma = n2.asExpr()
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)
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or
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exists(NewInstance ni |
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ni.getQualifier() = n1.asExpr() and
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ni = n2.asExpr()
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)
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or
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exists(MethodAccess ma |
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ma.getMethod() instanceof FragmentInstantiateMethod and
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ma.getArgument(1) = n1.asExpr() and
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ma = n2.asExpr()
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)
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}
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}

‎java/ql/lib/semmle/code/java/security/FragmentInjectionQuery.qll

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import java
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import semmle.code.java.dataflow.FlowSources
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import semmle.code.java.dataflow.TaintTracking
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import semmle.code.java.security.FragmentInjection
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/**
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* A taint-tracking configuration for unsafe user input
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* that is used to create Android Fragments dinamically.
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*/
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class FragmentInjectionTaintConf extends TaintTracking::Configuration {
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FragmentInjectionTaintConf() { this = "FragmentInjectionTaintConf" }
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override predicate isSource(DataFlow::Node source) { source instanceof RemoteFlowSource }
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override predicate isSink(DataFlow::Node sink) { sink instanceof FragmentInjectionSink }
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override predicate isAdditionalTaintStep(DataFlow::Node n1, DataFlow::Node n2) {
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any(FragmentInjectionAdditionalTaintStep c).step(n1, n2)
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}
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}

‎java/ql/src/Security/CWE/CWE-470/FragmentInjection.inc.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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Fragments are reusable parts of an Android application's user interface.
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Even though a Fragment controls its own lifecycle and layout and handles its input events,
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it cannot exist on its own: it must be hosted either by an Activity or another fragment.
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This means that a Fragment will be accessible by third-party applications (that is, exported)
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only if its hosting Activity is itself exported.
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</p>
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<p>
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If an exported Activity dinamically creates and hosts Fragments instantiated with externally
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provided names, a malicious application could provide the name of an arbitrary Fragment, even
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one not designed to be externally accessible, and inject it into the Activity, effectively
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bypassing access controls and exposing the application to unintended effects.
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</p>
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</overview>
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<recommendation>
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<p>
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In general, do not instantiate classes (including Fragments) with user-provided names
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without proper validation.
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Also, if an exported Activity is extending the <code>PreferenceActivity</code> class, make sure that
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the <code>isValidFragment</code> method is overriden and only returns <code>true</code> when the provided
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<code>fragmentName</code> points to an intended Fragment.
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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 following example shows two cases: in the first one, untrusted data is used to instantiate and
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add a Fragment to an Activity, while in the second one, a Fragment is safely added with a static name.
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</p>
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<sample src="FragmentInjection.java" />
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<p>
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The next example shows two Activities extending <code>PreferenceActivity</code>. The first one overrides
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<code>isValidFragment</code>, but it wrongly returns <code>true</code> inconditionally. The second Activity
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correctly overrides <code>isValidFragment</code> to only return <code>true</code> when <code>fragmentName</code>
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is a trusted Fragment name.
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</p>
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<sample src="FragmentInjectionInPreferenceActivity.java" />
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</example>
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<references>
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<li> Google Help:
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<a href="https://support.google.com/faqs/answer/7188427?hl=en">How to fix Fragment Injection vulnerability</a>.
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</li>
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<li>
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IBM Security Systems:
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<a href="https://securityintelligence.com/wp-content/uploads/2013/12/android-collapses-into-fragments.pdf">Android collapses into Fragments</a>.
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</li>
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<li>
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Android Developers:
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<a href="https://developer.android.com/guide/fragments">Fragments</a>
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</li>
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</references>
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</qhelp>

‎java/ql/src/Security/CWE/CWE-470/FragmentInjection.java

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public class MyActivity extends FragmentActivity {
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@Override
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protected void onCreate(Bundle savedInstance) {
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try {
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super.onCreate(savedInstance);
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// BAD: Fragment instantiated from user input
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{
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String fName = getIntent().getStringExtra("fragmentName");
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getFragmentManager().beginTransaction().replace(com.android.internal.R.id.prefs,
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Fragment.instantiate(this, fName, null)).commit();
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}
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// GOOD: Fragment instantiated statically
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{
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getFragmentManager().beginTransaction()
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.replace(com.android.internal.R.id.prefs, new MyFragment()).commit();
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}
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} catch (Exception e) {
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}
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}
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}

‎java/ql/src/Security/CWE/CWE-470/FragmentInjection.qhelp

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<!DOCTYPE qhelp PUBLIC "-//Semmle//qhelp//EN" "qhelp.dtd">
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<qhelp>
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<include src="FragmentInjection.inc.qhelp"></include>
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</qhelp>

‎java/ql/src/Security/CWE/CWE-470/FragmentInjection.ql

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/**
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* @name Android Fragment injection
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* @description Instantiating an Android Fragment from a user-provided value
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* may lead to Fragment injection.
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* @kind path-problem
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* @problem.severity error
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* @security-severity 9.8
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* @precision high
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* @id java/android/fragment-injection
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* @tags security
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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.security.FragmentInjectionQuery
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import DataFlow::PathGraph
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from DataFlow::PathNode source, DataFlow::PathNode sink
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where any(FragmentInjectionTaintConf conf).hasFlowPath(source, sink)
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select sink.getNode(), source, sink, "Fragment injection from $@.", source.getNode(),
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"this user input"

‎java/ql/test/query-tests/security/CWE-470/AndroidManifest.xml

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<?xml version="1.0" encoding="utf-8"?>
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<manifest
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xmlns:android="http://schemas.android.com/apk/res/android"
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android:versionCode="1"
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android:versionName="1.0"
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package="com.example.myapp">
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<application
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android:allowBackup="true"
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android:icon="@mipmap/ic_launcher"
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android:roundIcon="@mipmap/ic_launcher_round"
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android:label="@string/app_name"
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android:supportsRtl="true"
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android:theme="@style/AppTheme">
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<activity android:name=".MainActivity">
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<intent-filter>
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<action android:name="android.intent.action.MAIN" />
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<category android:name="android.intent.category.LAUNCHER" />
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</intent-filter>
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</activity>
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</application>
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</manifest>

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

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‎java/ql/test/query-tests/security/CWE-470/FragmentInjectionTest.ql

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import java
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import semmle.code.java.security.FragmentInjectionQuery
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import TestUtilities.InlineFlowTest
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class Test extends InlineFlowTest {
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override DataFlow::Configuration getValueFlowConfig() { none() }
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override TaintTracking::Configuration getTaintFlowConfig() {
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result instanceof FragmentInjectionTaintConf
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}
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}

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