Reading Contact Photos Without READ_CONTACTS A Google Messag...

src/mobile-pentesting/android-app-pentesting/drozer-tutorial/exploiting-content-providers.md

@@ -283,6 +283,71 @@ Vulnerable Providers:
   content://com.mwr.example.sieve.FileBackupProvider
 ```
 
+## Exported provider as a confused deputy
+
+An **exported** `ContentProvider` can become a **permission proxy** if it accepts a **caller-controlled backend URI** (for example via a path segment, query parameter, or `call()` bundle), dereferences that URI with the **provider app UID**, and then returns the resulting bytes to the lower-privileged caller.
+
+Typical bug pattern:
+
+- Provider is exported and reachable by untrusted apps
+- No caller permission, or a weak permission any app can hold
+- App has privileged access to another provider (for example Contacts, SMS, media, work-profile data)
+- External caller controls a backend `content://` URI that is later passed into `ContentResolver.query/openInputStream/openFileDescriptor/openAssetFileDescriptor`
+- Provider returns the original bytes or **derived output** (resized bitmap, transcoded PNG/JPEG, cached file, thumbnail)
+
+Why this matters:
+
+- The security boundary is enforced on the **UID performing the read**
+- A direct read from the attacker app may fail with `SecurityException`
+- The same URI may succeed when the victim provider reads it with its own permissions
+- **Rendering or transcoding does not remove the leak**: once protected data is converted to another format and streamed back, the permission boundary is already bypassed
+
+Minimal triage workflow:
+
+1. Enumerate exported providers and inspect manifest permissions (`readPermission`, `writePermission`, `grantUriPermissions`, path permissions)
+2. Reverse `query()`, `openFile()`, `openAssetFile()`, `openTypedAssetFile()`, and `call()` looking for attacker-controlled URIs
+3. Trace sinks such as:
+   - `Uri.parse(...)`
+   - `getQueryParameter(...)`
+   - `Bundle.getString(...)`
+   - `ContentResolver.query(...)`
+   - `openInputStream(...)`
+   - `openFileDescriptor(...)`
+4. Test the protected backend URI directly from a no-permission app to confirm it is blocked
+5. Send the **same** URI through the exported provider and compare the response
+
+ADB-style reproduction:
+
+```bash
+# Direct read from the attacker UID should fail
+adb shell am start -S -n com.local.probe/.ProbeActivity \
+  --es mode query-uri \
+  --es uri content://com.android.contacts/contacts/CONTACT_ID/photo
+
+# The same protected URI wrapped by the exported provider may succeed
+adb shell am start -S -n com.local.probe/.ProbeActivity \
+  --es mode query-uri \
+  --es uri 'content://com.victim.provider/r?m=content%3A%2F%2Fcom.android.contacts%2Fcontacts%2FCONTACT_ID%2Fphoto'
+```
+
+Common static signals:
+
+- `android:exported="true"` with no `readPermission` / `writePermission`
+- `grantUriPermissions="true"` combined with broad URI handling
+- Image/avatar/thumbnail/document preview providers that accept a source URI
+- Internal "safe URI" checks that only validate syntax/authority but **do not verify the original caller can access the source**
+
+Enumeration hint:
+
+If missing objects return a **stable fallback** (default avatar, placeholder thumbnail, empty file), the bug may be enumerable. Iterate predictable IDs and keep responses whose **size**, **hash**, or **decoded pixels** differ from the fallback.
+
+Safer design for developers:
+
+- Do not dereference untrusted external `content://` URIs with the app's ambient permissions
+- Prefer serving only app-owned opaque resources
+- If callers must provide a URI, require an explicit grant or verify the caller can access the source before reading it
+- Make the provider non-exported or protect it with a signature/internal permission unless cross-app access is really needed
+
 ## 2023-2025 Updates & Modern Tips
 
 ### Drozer 3.x (Python 3) is out
@@ -351,9 +416,6 @@ These changes in recent Android versions mean many legacy exploitation primitive
 - [https://labs.withsecure.com/content/dam/labs/docs/mwri-drozer-user-guide-2015-03-23.pdf](https://labs.withsecure.com/content/dam/labs/docs/mwri-drozer-user-guide-2015-03-23.pdf)
 - [https://github.com/WithSecureLabs/drozer/releases/tag/3.1.0](https://github.com/WithSecureLabs/drozer/releases/tag/3.1.0)
 - [https://source.android.com/security/bulletin/2024-07-01](https://source.android.com/security/bulletin/2024-07-01)
+- [Reading Contact Photos Without READ_CONTACTS: A Google Messages Confused Deputy Bug](https://blog.devploit.dev/posts/google-messages-avatarcontentprovider-contacts-bypass/)
 
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