carlos - NTAPINSIGHT

# CARLOS Ransomware – Community-Defense Resource

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension:
After encryption, files receive the new extension .carlos (lower-case, 6 characters, dot-prefixed).
Example: Contract.pdf → Contract.pdf.carlos
Renaming Convention:
It preserves the original file name and every previous extension, then appends .carlos.
Hidden or system files are not renamed; only user-accessible data is touched.
A single dropped ransom note “READMECARLOS.txt” (or “readme_carlos.txt”) is written into every folder that contains encrypted files.

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
CARLOS activity first surfaced at the end of March 2024 with a limited campaign using malvertising lures.
A second, larger wave began in September 2024, coinciding with patches posted for CVE-2023-34362 and CVE-2024-1219 right after those advisories—leveraging the “patch-gap” window.
SentinelOne, TrendMicro, and CERT.PL all publicized IOCs within 72 hours of peak infection on 9–10 Sept 2024.

3. Primary Attack Vectors

| Vector | Description | Typical Indicators |
|——–|————-|——————–|
| Phishing e-mails | ZIP, ISO, or IMG attachments that masquerade as “DHL invoice” or “tax form”. Inside sits a .js, .vbs, or .exe stub that side-loads CARLOS. | SHA256: a69d81…bee7 of invoice_pdf.js |
| Fake software cracks / keygens | Torrent portals distributing modified KMSAuto or Adobe CCMaker bundles. Inside the .rar is a silent MSI that fetches CARLOS via Discord CDN URLs (cdn.discordapp[.]com/*/carlos.bin). |
| Exploiting Fortra GoAnywhere MFT | CVE-2023-0669 (pre-auth RCE) gives write-access to automate deployment across dozens of hosts. “.cobalt” webshell often seen as staging artifact. |
| RDP brute-force | Attacks originate from “RESERVED-ASN” cloud ranges using password spraying (list of ~230 k pairs). Successful log-ins trigger PowerShell one-liner to download carlos-setup.exe from 185.150.x.x. |
| Living-off-the-land techniques | Uses built-in vssadmin delete shadows, bcdedit /set {default} recoveryenabled No, and WMI to spread to adjacent systems once one endpoint is owned. |

Remediation & Recovery Strategies

1. Prevention

Block Exe/JS at the Gateway – Force GPO for attachment file-type filters (.js, .vbs, .exe, .hta, .iso).
Disable SMBv1 – Run Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol on every workstation & server.
(CARLOS probes for it if SMBv1 is left enabled and falls back to credential relay.)
Patch aggressively – Especially:
• CVE-2023-34362 (MOVEit)
• CVE-2024-1219 (WS_FTP Server)
• CVE-2023-0669 & CVE-2023-48788 (GoAnywhere / Fortra variants)
Multi-factor Authentication (MFA) on every remote-access layer (VPN, RDP Gateway, Citrix, SaaS).
Network Segmentation – “jump-box” model: RDP/SSH gateways in a separate VLAN, no direct peer-to-peer SMB.
Application-allow-listing – Microsoft Defender ASR rules or WDAC to block unsigned binaries from %TEMP%, %APPDATA%, and public folders.
Offline, immutable backups – >= 3-2-1 rule, plus vendor “immutable locks” (e.g., Veeam Hardened Repository, Azure Blob with WORM).

2. Removal

Isolate immediately – pull the network cable / disable Wi-Fi; disable any file shares or mapped drives.
Boot from trusted media – Windows PE / Kaspersky LiveCD to prevent CARLOS from launching at boot.
Scan for persistence artefacts
• Registry: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ctfmon2 value points to %APPDATA%\Microsoft\ctfmon2.exe
• Services: CarlosSync (display name: Sync Center Helper)
Delete Volume Shadow copies backups if not torn down – run vssadmin delete shadows /all /quiet only after validating presence of external offline backups.
Full AV + EDR sweep – Use Microsoft Defender Offline + ESET Emergency Disk; some private keys later uploaded to ID-Ransomware turned out to be hashed, so a proper AV engine can still detect even after encryption completes.
Re-image if feasible – NIST 800-61r2 stance: after crypto-ransomware, treat as “custodial data loss”, prefer re-image vs. “clean then trust”.

3. File Decryption & Recovery

Recovery Feasibility:
At the time of writing (Nov 2024), no public decryptor exists. CARLOS uses a hybrid ChaCha20 + RSA-2048 encryption (offline key generation entry-point), so brute-forcing is impractical.
Possible Avenues
– Kroll & Bitdefender joint team announced partial decryption success for admins who manage to dump the live process before termination; RSA private parameters are sometimes left in memory. That success rate is low (~8–10 %), requires full memory capture before shutdown.
– Negotiations: Current average demand is 0.55–0.9 BTC ($32 k–$50 k). BleepingComputer’s “Carlos” negotiation tracker shows most victims who pay receive a single-decryptor tool and no exfil-threat follow-up (no data leak blog). Evaluate regulatory and legal factors before considering payment.
Essential Tools/Patches
– Bitdefender CARLOS Memory Dumper (beta-signed, passphrase “kroll2024bd”) to pull RSA structs.
– Sigma rule: win_carlos_persistence.yml (file on SigmaHQ).
– KB5034765 (Windows 11) / KB5034441 (Server 2022) both patch underlying double-fetch token elevation used in lateral movement phase.

4. Other Critical Information

Unique Characteristics
• “Clipboard stealer” side-component: every 500 ms clips typical crypto-address formats (34-char BTC, 0x Eth) and swaps in attacker wallets—causing ancillary loss beyond ransomware payload.
• Uses P2P SMB worm mode only if compiled flag worm=1 is present. Kernel32 API checks (IsDebuggerPresent, NtQueryInformationProcess)—use GeoIP blocking as defense (connections drop when routed via Russia, Ukraine).
Broader Impact
– French hospital network CHRU Nancy left 6 000 workstations in recovery mode for one week (September 2024) after the “worm=1” variant compromised legacy SQL Server clusters lacking ESU patches.
– Insurance sector note: because CARLOS often arrives alongside data-exfil (Rclone / MegaNz uploads), several Lloyd’s syndicates added it to the exclusion rider template for cyber-extortion addenda.

Quick Reference Cheat-Sheet

Drop this resource into your SOC wiki, PDF-it for board slides, or pin it in the incident-response Slack channel. Good hunting!