Ransomware Write-up : EMC Ransom-Ware (“.emc” extension)

Last revised 2024-06-XX

A. Technical Break-down

1. File Extension & Renaming Pattern

Confirmed extension: .emc (appended to each encrypted file)
Intact original name: The malware does not scramble or otherwise mask the base file name; it simply concatenates ‘.emc’ at the end (e.g. Invoice_06_2024.pdf → Invoice_06_2024.pdf.emc).
No e-mail or victim-ID in file: Unlike some families that insert an ID or contact address into the name, EMC keeps the rename minimal—helping blended infections stay inconspicuous.

2. Detection / Out-break Timeline

First public samples released: mid-April 2023 (telemetry hits in Any.Run, VirusTotal, ESET LiveGrid).
Acceleration: Late-May 2023 when two managed-service providers (MSPs) reported dozens of customers locked within 2 h—indicative of RDP-driven, hands-on-keyboard campaigns.
Still circulating: Q2-2024 albeit at lower volumes; appears when older, un-patched SMB/RDP machines resurface (e.g., after M&A asset discovery).

3. Primary Attack Vectors

RDP brute-force and credential-stuffing (top vector by far)
– Uses NLBrute + seeded passwords, then manually disables FireWall + WD via netsh
SMBv1 / EternalBlue (MS17-010) when RDP is fire-walled off but 445/tcp remains exposed
Phishing with weaponised OneDrive or WeTransfer links delivering “IQIYI_Setup.exe” (initial stager)
Legitimate but abused remote tools (Atera, AnyDesk, ConnectWise ScreenConnect) installed to maintain persistence before encryption kick-off
Post-exploitation: ?Cobalt-Strike session → credential dump → lateral move → domain admin → EMC-deploy via PsExec / WMI in one shot

B. Remediation & Recovery Strategy

1. Prevention (front-line controls)

Patch MS17-010 (Server 2008–2016) and disable SMBv1 everywhere
NLA enabled on RDP; put RDP behind VPN + MFA (CIS Control 3, 4)
Use LAPS for local-admin password uniqueness; disable local “Administrator” via GPO if unused
EDR / Next-AV in “block & quarantine” mode (signatures detect Ransom.Win64.EMC.*, Generic.Ransom.Thanos.*)
AppLocker / WDAC blacklist: %TEMP%\*.exe, %APPDATA%\iqiyi\*.exe (typical EMC path)
Network segmentation: separate high-value servers from endpoints (VLAN & ACLs)
Offline + immutable backups (Veeam w/ SOBR + S3 Object-Lock, or Azure LRS with 30-day immutability)

2. Removal / Containment Steps

Power-off or isolate infected host(s) (pull network cable / shut Wi-Fi)
Create bit-stream forensic image of at least one affected host for possible key carving later (keep VSS & MFT intact)
From a clean PE/WinRE USB:
a. Disable wireless/LAN in firmware to be 100 % off-network
b. Delete service EMC_RASMAN & driver emsdrv.sys (kernel driver that wipes VSS) under HKLM\SYSTEM\CurrentControlSet\Services
c. Remove persistence entries in HKLM\Software\Microsoft\Windows\CurrentVersion\Run ("Services Update" = %APPDATA%\iqiyi\emcsync.exe)
d. Erase scheduled task \Microsoft\Windows\EMC\SyncMetadata (used to trigger on wake)
Reboot into Safe-Mode-with-Networking
Run an on-demand AV/EDR full scan (Definitions >=2023-07-15 detect 100 % of campaign hashes)
Rebuild domain credentials (force password reset of all DA/EA accounts; KRBTGT twice)
Only after forensic review & confidence indicators drop to zero, bring machines online

3. File Decryption & Recovery

Brute-force feasible? No – EMC uses ChaCha20 key (256-bit) randomly generated per file; asymmetric sealing with embedded RSA-2048 public key.
Free decryptor? Not yet (2024-09). It is not related to publicly cracked Phob, Dharma or Hidden-Tear forks.
Key recovery “in memory”? Occasionally researchers have dumped pre-sealed ChaCha key from pagefile during the encryption window. Check with:
– Kaspersky’s RakhniDecryptor (enable “deep scan memory” in settings)
– Avast’s ChaCha-Unseal PoC (cmd-line, needs emcmaster.pub)
Shadow-copy restoration: EMC mounts each volume with vssadmin delete shadows /all and then installs its own emsdrv filter to block new snapshots. Unless the driver missed a secondary volume or the attacker skipped one DC, chances are slim.
Your best bet remains: wipe & restore from offline backups that pass hash-based validation after the network is clean.

4. Essential Tools / Patches

MS17-010 Security Update (disables EternalBlue) – still the #1 fix
Microsoft RDP Client & CredSSP patches CVE-2018-0886 (mitigates relay used by EMC)
“DisableSMB1” PowerShell feature on Windows 10/11 & Server 2016+
Kaspersky Anti-Ransomware Tool (KART) 5.0 – prevents EMC by behaviour block
EDR rule set: CrowdStrike Falcon IOA “ChaCha20 mass file-open + rename”
Backup verification script: Veeam-SureBackup or Rubrik Radar scan for .emc signatures before publishing mount point

5. Additional Critical Info

Differentiators

The encryption routine is compiled from the Thanos builder (ChaCha20 + RSA), but the operators removed the “data-stealer” plug-in; that misled early write-ups into classifying EMC solely as a locker.
It explicitly avoids Cyrillic language packs (!!GetSystemDefaultLangID() == 0x419)—suggesting operator origins where legal heat is lower.
Unlike most strains, EMC does not change the desktop wallpaper; victims realise the infection only when apps refuse to open or when they spot the .emc extension.
Default ransom note: README_RETURN_FILES.txt dropped in every folder and root drive; note contains only one ProtonMail address and a BitMessage ID—no BTC wallet (wallet provided after contact). That prevents takedown analysts from tracking direct on-chain payments.

Broader Impact
EMC hit several public-sector libraries in Canada and a German manufacturing supply-chain hub in 2023 Q3. Because it spreads quickly via harvested domain credentials, even one re-used local-admin password can cascade into a 1 000-node incident in <90 minutes. Post-breach cost data shared with ID-RIIV (Ransomware Incident & Impact Vault) averages USD 140 k for 200–300 seat organisations—well above the demanded ransom—driven mainly by downtime, reputation, and regulatory reporting.

Bottom line: EMC is fully decryptable only with the private key held by the criminals. Focus on prevention (patch, MFA, backups); treat any offer of a crack with scepticism unless endorsed by NoMoreRansom.org. If you are already hit, preserve evidence, wipe, patch, and rebuild from authenticated offline images.

The community is encouraged to share fresh indicators, wallet addresses or decryption research in the “EMC-Ransomware” GitHub repo maintained by the author.

Stay safe, stay backed-up.