Inside an N26 Impersonation Campaign From Vishing and Fake C...

src/generic-methodologies-and-resources/basic-forensic-methodology/android-malware-post-exploitation.md

@@ -1,7 +1,5 @@
 # Android Malware Post-Exploitation
 
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 This page collects Android malware behavior that happens after installation or execution: payload staging, persistence, C2, Accessibility-driven control, overlays, SMS/OTP abuse, fraud automation, and botnet tasking. Keep Android app pentesting methodology focused on testing legitimate apps, and use this page when reversing malicious Android samples or documenting post-install tradecraft.
 
 ## C2-Gated Permission Abuse and Background Collection
@@ -51,13 +49,15 @@ Triage ideas:
 - full routes present but no forwarding path from the TUN reader back to a socket / output stream
 - setup-themed notifications while only a few apps retain connectivity
 
+A narrower variant sends **only** Google Play Store traffic into the blackhole by calling `addAllowedApplication("com.android.vending")`. One observed dropper installed IPv4 and IPv6 routes, discarded the resulting TUN packets for 240 seconds, and polled the unknown-source permission every 800 ms so sideloading resumed immediately after approval.<sup>[[19]](#references)</sup> Hunt for `addAllowedApplication("com.android.vending")`, a `240000` teardown timer, and `PackageInstaller` calls in the same path.
+
 ### Facade UI and Collection
 
 The app may show harmless views such as an SMS viewer or gallery picker while background collection starts:
 
 - IMEI / IMSI, phone number
 - Full `ContactsContract` dump as JSON
-- JPEG/PNG from `/sdcard/DCIM`, often compressed with [Luban](https://github.com/Curzibn/Luban) to reduce size<sup>[[5]](#references)</sup>
+- JPEG/PNG from `/sdcard/DCIM`, often compressed with [Luban](https://github.com/Curzibn/Luban) to reduce size.<sup>[[5]](#references)</sup>
 - Optional SMS content from `content://sms`
 
 Payloads are commonly batch-zipped and sent via HTTP endpoints such as `/upload.php`.
@@ -144,6 +144,28 @@ Triage ideas:
 - `Application.attachBaseContext` doing large asset reads before any UI is created
 - fake media/font assets later passed into `ZipInputStream`, `DexClassLoader`, or custom RC4 helpers
 - reflection on `pathList`, `dexElements`, `ContextImpl`, or `LoadedApk` close to asset decryption
+- compare every activity, service, and receiver declared in `AndroidManifest.xml` against **all** packaged `classes*.dex` files; components that resolve only after an asset is decrypted are strong staged-loader indicators.<sup>[[15]](#references)[[21]](#references)</sup>
+
+### Asset-to-`PackageInstaller` staging and nested child payloads
+
+Another useful evasion pattern is to hide stage 2 inside `assets/` and **stream it directly into a `PackageInstaller` session** instead of first dropping a plainly named APK in shared storage. In the Octagon chain, the installed child then generated a JAR under its private `app_walk` directory and dynamically loaded the final module.<sup>[[15]](#references)[[21]](#references)</sup>
+
+Hunting ideas:
+- correlate `ACTION_MANAGE_UNKNOWN_APP_SOURCES` / `REQUEST_INSTALL_PACKAGES` with `PackageInstaller.createSession` -> `openWrite` -> `fsync` -> `commit`
+- watch for the parent package stopping a temporary service (often VPN / overlay / lure UI) immediately after install, then launching the new package
+- inspect `PACKAGE_ADDED` / `PACKAGE_REPLACED` receivers, private `app_*` directories, and follow-on `DexClassLoader` activity in the child app
+
+### `AccountManager` + Sync Adapter persistence
+
+A less common but very useful Android persistence primitive is to register a **fake account** and attach a **Sync Adapter** to it. Octagon registered the `OctagonPanel` account, scheduled synchronization every 30 minutes, and could request an immediate synchronization to resume activity or reconnect to C2.<sup>[[21]](#references)</sup>
+
+What to look for:
+- authenticator XML/resources plus code calling `AccountManager.addAccountExplicitly`
+- a sync adapter service with `android.content.SyncAdapter` metadata
+- suspicious sync intervals (for example every 30 minutes) or forced immediate sync right after connectivity returns
+- boot receivers / WorkManager jobs whose only purpose is to re-register the account or reschedule sync
+
+This is especially useful in samples that already store queue/state locally (SQLite + SharedPreferences): periodic sync becomes the exfil/reconnect trigger for offline-collected SMS, credential captures, contacts, or phishing results.
 
 ### Anti-analysis kill-switch
 
@@ -589,7 +611,7 @@ Note: Many DevicePolicyManager controls require Device Owner/Profile Owner on re
 ### NFC relay orchestration (NFSkate)
 Stage-3 can install and launch an external NFC-relay module (e.g., NFSkate) and even hand it an HTML template to guide the victim during the relay. This enables contactless card-present cash-out alongside online ATS.<sup>[[12]](#references)</sup>
 
-Background: [NFSkate NFC relay](https://www.threatfabric.com/blogs/ghost-tap-new-cash-out-tactic-with-nfc-relay).
+Background: [NFSkate NFC relay](https://www.threatfabric.com/blogs/ghost-tap-new-cash-out-tactic-with-nfc-relay).<sup>[[12]](#references)</sup>
 
 ### Operator command set (sample)
 - UI/state: `txt_screen`, `screen_live`, `display`, `record`
@@ -860,6 +882,57 @@ struct Header {
 - Once verified, the bot sends a `MsgType=0` body carrying the operator-defined **group string** (e.g. `android-postboot-rt`). If the group is enabled, the C2 responds with `MsgType=2 (confirm)`, after which tasking (MsgType 5–12) begins.
 - Supported verbs include SOCKS-style TCP/UDP proxying (residential proxy monetization), reverse shell / single command exec, file read/write, and **Mirai-compatible DDoSBody** payloads (same `AtkType`, `Duration`, `Targets[]`, `Flags[]` layout).
 
+
+## Copybara-style banker / RAT tradecraft: parser differentials and decoy overlays
+
+### Hostile APK/ZIP parser differentials
+
+Some droppers intentionally build APKs that Android or tolerant ZIP readers can still process while common analysis tooling disagrees about the file layout.<sup>[[19]](#references)</sup>
+
+Interesting anti-analysis shapes:
+- **local-header vs central-directory mismatches** (for example different compression methods for the same entry)
+- **oversized ZIP extra fields** and random Unicode path components
+- **extremely long asset names** used to hide the real payload near the end of a path that desktop tools fail to materialize
+- **file-versus-directory collisions** below names normally treated as files, such as `classes.dex/`, `AndroidManifest.xml/`, or `resources.arsc/`
+
+Practical workflow:
+
+```bash
+zipinfo -v sample.apk
+7z l sample.apk
+bsdtar -tf sample.apk
+python -m zipfile -l sample.apk
+jadx sample.apk -d out-jadx
+apktool d sample.apk -o out-apktool
+```
+
+If these tools produce different entry lists, or one sees `classes.dex` while another sees children under `classes.dex/`, treat the APK as **parser-differential anti-analysis** rather than a broken download. [apkInspector](https://github.com/erev0s/apkInspector/) can compare local headers with the central directory and flag path collisions and other tampering indicators.<sup>[[20]](#references)</sup>
+
+In the analyzed Copybara chain, the outer APK concealed an RC4-encrypted JAR at the tail of a 2,441-byte asset path. Decrypting that JAR exposed a DEX loader that located and installed the final `assets/base.apk` payload.<sup>[[19]](#references)</sup> This is a useful extension of the earlier `attachBaseContext()` triage: inspect the tail of abnormally long assets even when the visible application code appears to contain only lure UI and permission handling.
+
+### Context hiding instead of biometric bypass
+
+Accessibility bankers do not always need to break biometric crypto. A full-screen branded loading page or a generic utility **WebView decoy** can hide the real app while Accessibility performs taps underneath. If the victim is tricked into approving a genuine biometric / system prompt whose context is concealed, the attacker gets authorization **without** bypassing the biometric primitive itself.<sup>[[19]](#references)</sup>
+
+Operational clues:
+- locale-driven HTML decoys such as `pg-en.html`, `pg-it.html`, ... loaded full-screen in a `WebView`
+- hard-coded battery / temperature / RAM values used only to make the decoy look alive
+- `TYPE_ACCESSIBILITY_OVERLAY` or opaque activity screens shown while `dispatchGesture`, `ACTION_SET_TEXT`, `performGlobalAction`, or notification suppression runs in parallel
+- strings / structures indicating **server-defined overlays**, e.g. an `inj` object containing `package` + template filename so new target apps can be added without rebuilding the APK
+
+### Split MQTT control/media channels for Accessibility RATs
+
+One analyzed Copybara payload used TCP port `52997` for its primary MQTT channel and port `52998` for camera and MediaProjection traffic. It subscribed to `commands_FromPC`, registered through `RegisterMyDevice`, and substituted the Android ID into the registration payload.<sup>[[19]](#references)</sup>
+
+A practical pattern to hunt for:
+- MQTT topic such as `commands_FromPC` for serialized commands
+- separate registration topic such as `RegisterMyDevice`
+- one port/channel for command dispatch and a second port/channel for MediaProjection or camera traffic
+- Android ID or a similarly stable device identifier substituted into the registration payload before subscription/publish
+
+Separating these channels can keep UI automation responsive while heavier screen or camera data uses a different socket or QoS profile.
+
+
 ## References
 
 - [1] [Premium Deception: Uncovering a Global Android Carrier Billing Fraud Campaign](https://zimperium.com/blog/premium-deception-uncovering-a-global-android-carrier-billing-fraud-campaign)
@@ -880,5 +953,8 @@ struct Header {
 - [16] [Rokarolla : Android Banker with Complete Device Takeover Capabilities](https://zimperium.com/blog/rokarolla-android-banker-with-complete-device-takeover-capabilities)
 - [17] [Zimperium IOC – Rokarolla commands](https://github.com/Zimperium/IOC/blob/master/2026-06-Rokarolla/commands.md)
 - [18] [Kimwolf Android TV Botnet: ENS-Based C2 Evasion, TLS+ECDSA C2 Protocol, and Large-Scale Proxy/DDoS Operations](https://blog.xlab.qianxin.com/kimwolf-botnet-en/)
+- [19] [Inside an N26 Impersonation Campaign: From Vishing and Fake Control 1.0 to the Copybara Android RAT](https://d3lab.net/inside-an-n26-impersonation-campaign-from-vishing-and-fake-control-1-0-to-the-copybara-android-rat)
+- [20] [apkInspector](https://github.com/erev0s/apkInspector/)
+- [21] [Octagon: Technical Analysis of a Fake Bahrain Civil Defense Application](https://labs.k7computing.com/index.php/octagon-technical-analysis-of-a-fake-bahrain-civil-defense-application/)
 
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