I’ve been digging into this Arsink RAT campaign that’s got everyone talking, and man, it’s a slick one.

These threat actors are straight-up hijacking legit cloud services to run their command-and-control and vacuum up data from Android devices worldwide.

It slips right past old-school defenses by hiding in traffic we all allow, racking up 45,000 unique victim IPs across 143 countries through 1,216 different APK variants.

They’re chaining Firebase Realtime Database, Google Apps Script, and Telegram into this tough-as-nails C2 setup, flipping trusted tools into their personal playground.

The heart of it? Arsink leans hard on everyday cloud APIs. Firebase RTDB, that go-to for mobile devs syncing data in real time, ends up warehousing stolen goodies like creds, device fingerprints, locations, and keystrokes. Google Apps Script jumps in to automate the grunt work, checking Firebase for orders and shoving them out to the bots.

Telegram handles the sneaky back-and-forth chats between infected phones and the bad guys.

This three-way combo gives them storage, brains, and comms that’s dirt cheap, super resilient, and a nightmare to knock offline.

Infection Chains and APK Proliferation

Arsink mostly sneaks in via dodgy Android APKs posing as handy apps, games, or tweaks, you name it, from sketchy app markets, Telegram drops, or phishing hooks.

When you crack one open in IDA or Jadx, you see the usual suspects: ProGuard mangling everything, base64 blobs hiding payloads, DexClassLoader slurping in fresh code on the fly.

Sideloading kicks it off, dodging Play Protect, then it grabs perms for SMS, contacts, accessibility, and overlays to start slurping keys and snapping screens.

To stick around, it starts a foreground service pretending to be a system service, like “com.android.systemui.update.” Right away, it IDs the device Android ID, IMEI, model, and carrier, all SHA-256 hashed and shipped to Firebase under paths like /arsink/victims/{device_id}.

We’ve got SHA256s from late 2025 variants pointing to some automated factory, probably abusing GitHub Actions or whatever to pump out new builds that VirusTotal struggles to group.

The numbers are wild: 1,216 APKs, each with its own sig but telltale strings like “arsink_c2_firebase” in the smali guts. Looks like scripted repacks with Frida or even AI cooking up lures. Hotspots? India, for all the sideloading love, the US, Europe, and heavily in Southeast Asia’s bazaar markets.

C2 Mechanics: Firebase as the Nerve Center

Firebase RTDB runs the show. Crooks spin up anonymous projects using pilfered accounts or trial accounts, then set public writable nodes. Bots log in anonymously via the Firebase Auth SDK and listen on /commands/{bot_id}.

Orders are sent as JSON, like {“action”: “keylog”, “duration”: 3600, “target”: “com.whatsapp”}. The bot fires it up with Java Reflection, hitting AccessibilityService to nab inputs.

Data dumps to /data/{bot_id}/{timestamp}, batched every 5-10 minutes to look like everyday app chatter.

Google Apps Script supercharges it: Webhooks poll the RTDB hourly, crunch commands (e.g., prioritizing bank apps), and ping Telegram via the Bot API. They use UrlFetchApp for POST requests and AES-256 encryption with PBKDF2-derived keys derived from the bot ID. Pulled this GAS bit from a teardown:

Telegram’s Role in Evasion and Persistence

Telegram ties it together for that extra stealth. Bots join hidden supergroups via baked-in invite links like t.me/+abc123. C2 rolls through self-destruct msgs and polls: Grab tasks like “sms_dump” or “file_exfil.” Responses go as document uploads up to 50MB, and the names are all jumbled like “log_0x7f.pdf.” Double-encrypted with MTProto plus a custom XOR key.

It loves Telegram’s E2EE secret chats and hands-off bot policies. Your firewall sees 149.154.160.0/20 IP addresses that we all allow.

Subtle red flags? Weird poll spikes or fat doc sends, but most EDR skips it sans cloud logs.

function pollCommands() {
  var db = SpreadsheetApp.openById('...').getSheetByName('FirebaseProxy');
  // Pull from RTDB via REST API, relay to Telegram
  UrlFetchApp.fetch('https://api.telegram.org/bot<TOKEN>/sendMessage', {
    method: 'POST',
    payload: JSON.stringify({chat_id: '<GROUP>', text: cmd})
  });
}

Technical Evasion and Anti-Analysis Tricks

Arsink’s loaded with tricks. It sniffs Build.TAGS for “eng” or “userdebug” to bail on emus with System. exit(0).

Hooks Frida’s usual spots like Runtime.exec() and fuzzes traces of Firebase WebSockets (wss://*.firebaseio.com) with a Poisson λ=300s jitter to shake timing rules.

Forensics-wise, it chunks, gzips, base64s data before upload: no bricks or ransom, just quiet stealing to keep bots milking.

Variants have “dead drop” fallbacks: Firebase down? Apps Script direct or Telegram solo.

Global Footprint and Attribution Clues

Sinkhole and ETPRO data show 45,000+ IPs, peaking in India (15%), Indonesia (12%), Brazil (8%), and Russia (7%). Mobile ASNs dominate: Jio, Telkomsel, Vivo.

No slam-dunk attribution, but Telegram bot overlaps with RustDoor’s ‘Eastern Europe’ scream. Leaky Firebase IDs like arsink-prod-2025 and GAS “C2RelayV2” help chase ’em.

Detection Signatures and IOCs

Key hunters for your toolkit:

YARA (APK scan):

rule Arsink_APK {
  strings: $s1 = "arsink_c2_firebase" ascii wide
  $s2 = "/victims/%s/data" fullword
  condition: all of them
}

Network IOCs:

Type	Indicator	Description
Firebase URL	*.firebaseio.com/arsink/	RTDB paths
GAS Endpoint	script.google.com/macros/s/.../exec	C2 proxy
Telegram Bot	Tokens starting 12345:ABC...	Observed in samples

Behavioral Sigma:

• Android AccessibilityService granting overlay + Firebase connects.
• WebSocket to firebaseio.com with JSON payloads >1KB every 5min.
• Telegram API calls from non-browser UAs.

Mitigation and Hardening Strategies

Time to level up. On-device, roll MTD like Zimperium or Lookout for APK checks and hook spotting.

Networks? CASB proxy on Firebase/Telegram with DLP sniffing JSON. Behavioral stuff catches “Accessibility + cloud dumps.”

Orgs: MDM no-sideloading, Firebase API key allowlists, Workspace logs for GAS. Users: Play Store only, Protect on, perm audits via adb.

Future Outlook: Cloud Malware’s Escalation

Arsink’s a wake-up next up, Lambda or Azure Functions RATs. Scale screams for AI UEBA on APIs.

Takedowns? Firebase reports crawl, Telegram ghosts DMCA. Mobile needs sandbox mandates, global APK blocks. This RAT’s no fluke; it’s the new playbook for cloud-owned persistence.

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