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Merge pull request #9983 from jcogs33/android-implicit-export
Java: query to detect implicitly exported Android components
2 parents 610c788 + 0136c75 commit b3e88f8

15 files changed

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‎java/ql/lib/change-notes/2022-08-09-android-manifest-new-class-and-predicates.md‎

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---
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category: feature
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---
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* Added a new predicate, `requiresPermissions`, in the `AndroidComponentXmlElement` and `AndroidApplicationXmlElement` classes to detect if the element has explicitly set a value for its `android:permission` attribute.
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* Added a new predicate, `hasAnIntentFilterElement`, in the `AndroidComponentXmlElement` class to detect if a component contains an intent filter element.
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* Added a new predicate, `hasExportedAttribute`, in the `AndroidComponentXmlElement` class to detect if a component has an `android:exported` attribute.
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* Added a new class, `AndroidCategoryXmlElement`, to represent a category element in an Android manifest file.
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* Added a new predicate, `getACategoryElement`, in the `AndroidIntentFilterXmlElement` class to get a category element of an intent filter.

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

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/** Provides a class to identify implicitly exported Android components. */
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private import semmle.code.xml.AndroidManifest
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/**
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* An Android component without an `exported` attribute explicitly set
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* that also has an `intent-filter` element.
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*/
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class ImplicitlyExportedAndroidComponent extends AndroidComponentXmlElement {
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ImplicitlyExportedAndroidComponent() {
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this.hasAnIntentFilterElement() and
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not this.hasExportedAttribute() and
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// Components with category LAUNCHER or with action MAIN need to be exported since
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// they are entry-points to the application. As a result, we do not consider these
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// components to be implicitly exported since the developer intends them to be exported anyways.
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not this.getAnIntentFilterElement().getACategoryElement().getCategoryName() =
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"android.intent.category.LAUNCHER" and
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not this.getAnIntentFilterElement().getAnActionElement().getActionName() =
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"android.intent.action.MAIN" and
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// The `permission` attribute can be used to limit components' exposure to other applications.
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// As a result, we do not consider components with an explicitly set `permission` attribute to be
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// implicitly exported since the developer has already limited access to such components.
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not this.requiresPermissions() and
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not this.getParent().(AndroidApplicationXmlElement).requiresPermissions() and
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not this.getFile().(AndroidManifestXmlFile).isInBuildDirectory()
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}
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}

‎java/ql/lib/semmle/code/xml/AndroidManifest.qll‎

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@@ -67,6 +67,11 @@ class AndroidApplicationXmlElement extends XmlElement {
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attr.getValue() = "true"
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)
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}
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/**
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* Holds if this application element has explicitly set a value for its `android:permission` attribute.
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*/
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predicate requiresPermissions() { this.getAnAttribute().(AndroidPermissionXmlAttribute).isFull() }
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}
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/**
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* `android:permission` attribute or its `android:readPermission` and `android:writePermission`
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* attributes.
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*/
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predicate requiresPermissions() {
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override predicate requiresPermissions() {
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this.getAnAttribute().(AndroidPermissionXmlAttribute).isFull()
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or
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this.getAnAttribute().(AndroidPermissionXmlAttribute).isWrite() and
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*/
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AndroidIntentFilterXmlElement getAnIntentFilterElement() { result = this.getAChild() }
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/**
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* Holds if this component element has an `<intent-filter>` child element.
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*/
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predicate hasAnIntentFilterElement() { exists(this.getAnIntentFilterElement()) }
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/**
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* Gets the value of the `android:name` attribute of this component element.
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*/
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* Holds if the `android:exported` attribute of this component element is explicitly set to `false`.
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*/
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predicate isNotExported() { this.getExportedAttributeValue() = "false" }
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/**
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* Holds if this component element has an `android:exported` attribute.
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*/
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predicate hasExportedAttribute() { exists(this.getExportedAttributeValue()) }
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/**
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* Holds if this component element has explicitly set a value for its `android:permission` attribute.
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*/
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predicate requiresPermissions() { this.getAnAttribute().(AndroidPermissionXmlAttribute).isFull() }
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}
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/**
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* Gets an `<action>` child element of this `<intent-filter>` element.
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*/
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AndroidActionXmlElement getAnActionElement() { result = this.getAChild() }
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/**
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* Gets a `<category>` child element of this `<intent-filter>` element.
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*/
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AndroidCategoryXmlElement getACategoryElement() { result = this.getAChild() }
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}
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/**
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)
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}
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}
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/**
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* A `<category>` element in an Android manifest file.
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*/
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class AndroidCategoryXmlElement extends XmlElement {
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AndroidCategoryXmlElement() {
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this.getFile() instanceof AndroidManifestXmlFile and this.getName() = "category"
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}
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/**
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* Gets the name of this category.
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*/
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string getCategoryName() {
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exists(XmlAttribute attr |
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attr = this.getAnAttribute() and
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attr.getNamespace().getPrefix() = "android" and
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attr.getName() = "name"
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|
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result = attr.getValue()
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)
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}
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}

‎java/ql/src/Security/CWE/CWE-926/ExampleBad.xml‎

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<manifest ... >
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<application ...
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<!-- BAD: this component is implicitly exported -->
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<activity>
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android:name=".Activity">
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<intent-filter>
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<action android:name="android.intent.action.VIEW" />
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</intent-filter>
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</activity>
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</application>
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</manifest>

‎java/ql/src/Security/CWE/CWE-926/ExampleGood.xml‎

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<manifest ... >
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<application ...
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<!-- GOOD: this component is not exported due to 'android:exported' explicitly set to 'false'-->
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<activity>
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android:name=".Activity">
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android:exported="false"
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<intent-filter>
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<action android:name="android.intent.action.VIEW" />
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</intent-filter>
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</activity>
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</application>
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</manifest>

‎java/ql/src/Security/CWE/CWE-926/ImplicitlyExportedAndroidComponent.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>The Android manifest file defines configuration settings for Android applications.
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In this file, components can be declared with intent filters which specify what the components can do and what types
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of intents the components can respond to. If the <code>android:exported</code> attribute is omitted from the component
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when an intent filter is included, then the component will be implicitly exported.</p>
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<p>An implicitly exported component could allow for improper access to the component and its data.</p>
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</overview>
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<recommendation>
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<p>Explicitly set the <code>android:exported</code> attribute for every component or use permissions to limit access to the component.</p>
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</recommendation>
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<example>
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<p>In the example below, the <code>android:exported</code> attribute is omitted when an intent filter is used.</p>
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<sample src="ExampleBad.xml" />
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<p>A corrected version sets the <code>android:exported</code> attribute to <code>false</code>.</p>
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<sample src="ExampleGood.xml" />
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</example>
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<references>
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<li>
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Android Developers:
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<a href="https://developer.android.com/guide/topics/manifest/manifest-intro">App Manifest Overview</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/topics/manifest/intent-filter-element">The &lt;intent-filter&gt; element</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/topics/manifest/activity-element#exported">The android:exported attribute</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/topics/manifest/activity-element#prmsn">The android:permission attribute</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/about/versions/12/behavior-changes-12#exported">Safer component exporting</a>.
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</li>
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</references>
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</qhelp>

‎java/ql/src/Security/CWE/CWE-926/ImplicitlyExportedAndroidComponent.ql‎

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/**
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* @name Implicitly exported Android component
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* @description Android components with an '<intent-filter>' and no 'android:exported' attribute are implicitly exported, which can allow for improper access to the components themselves and to their data.
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* @kind problem
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* @problem.severity warning
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* @security-severity 8.2
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* @id java/android/implicitly-exported-component
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* @tags security
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* external/cwe/cwe-926
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* @precision high
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*/
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import java
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import semmle.code.java.security.ImplicitlyExportedAndroidComponent
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from ImplicitlyExportedAndroidComponent impExpAndroidComp
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select impExpAndroidComp, "This component is implicitly exported."

‎java/ql/src/change-notes/2022-08-09-android-implicit-export.md‎

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---
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category: newQuery
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---
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* Added a new query, `java/android/implicitly-exported-component`, to detect if components are implicitly exported in the Android manifest.

‎java/ql/test/query-tests/security/CWE-926/AndroidManifest.xml‎

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<?xml version="1.0" encoding="utf-8"?>
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<manifest xmlns:android="http://schemas.android.com/apk/res/android"
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xmlns:tools="http://schemas.android.com/tools"
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package="com.example.happybirthday">
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<application
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android:allowBackup="true"
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android:dataExtractionRules="@xml/data_extraction_rules"
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android:fullBackupContent="@xml/backup_rules"
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android:icon="@mipmap/ic_launcher"
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android:label="@string/app_name"
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android:roundIcon="@mipmap/ic_launcher_round"
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android:supportsRtl="true"
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android:theme="@style/Theme.HappyBirthday"
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tools:targetApi="31">
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<!-- $ hasImplicitExport --> <activity
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android:name=".Activity">
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<intent-filter>
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<action android:name="android.intent.action.VIEW" />
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</intent-filter>
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</activity>
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<!-- $ hasImplicitExport --> <receiver
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android:name=".CheckInstall">
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<intent-filter>
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<action android:name="android.intent.action.PACKAGE_INSTALL"/>
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</intent-filter>
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</receiver>
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<!-- $ hasImplicitExport --> <service
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android:name=".backgroundService">
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<intent-filter>
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<action android:name="android.intent.action.START_BACKGROUND"/>
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</intent-filter>
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</service>
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<!-- $ hasImplicitExport --> <provider
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android:name=".MyCloudProvider">
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<intent-filter>
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<action android:name="android.intent.action.DOCUMENTS_PROVIDER"/>
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</intent-filter>
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</provider>
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<!-- Safe: 'android:exported' explicitly set --> <activity
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android:name=".Activity"
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android:exported="true">
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<intent-filter>
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<action android:name="android.intent.action.VIEW" />
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</intent-filter>
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</activity>
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<!-- Safe: no intent filter --> <activity
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android:name=".Activity">
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</activity>
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<!-- Safe: has 'permission' attribute --> <activity
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android:name=".Activity"
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android:permission=".Test">
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<intent-filter>
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<action android:name="android.intent.action.VIEW" />
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</intent-filter>
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</activity>
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<!-- Safe: 'provider' with read and write permissions set --> <provider
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android:name=".MyCloudProvider"
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android:readPermission=".TestRead"
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android:writePermission=".TestWrite">
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<intent-filter>
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<action android:name="android.intent.action.DOCUMENTS_PROVIDER"/>
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</intent-filter>
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</provider>
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<!-- $ hasImplicitExport --> <provider
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android:name=".MyCloudProvider"
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android:readPermission=".TestRead">
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<intent-filter>
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<action android:name="android.intent.action.DOCUMENTS_PROVIDER"/>
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</intent-filter>
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</provider>
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<!-- $ hasImplicitExport --> <provider
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android:name=".MyCloudProvider"
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android:writePermission=".TestWrite">
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<intent-filter>
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<action android:name="android.intent.action.DOCUMENTS_PROVIDER"/>
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</intent-filter>
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</provider>
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<!-- Safe: has category 'android.intent.category.LAUNCHER' --> <activity
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android:name=".Activity">
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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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<!-- Safe: has action 'android.intent.category.MAIN' --> <activity
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android:name=".Activity">
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<intent-filter>
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<action android:name="android.intent.action.MAIN" />
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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-926/ImplicitlyExportedAndroidComponentTest.expected‎

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