escal*

[Content by Gemini 2.5]

Technical Breakdown – Escal Ransomware (.ESCAL)

1. File Extension & Renaming Patterns

• Confirmation of file extension:
– Exact extension appended is “.ESCAL” (upper-case or lower-case depending on sample).
• Renaming convention:
– Files are renamed in the pattern:
<original file-name>.<original extension>.<victim-ID>.ESCAL
Example:
project.xlsx → project.xlsx.8B0C5F7A.ESCAL
– The 8-character victim-ID is unique per campaign and is later needed by the attacker to generate the correct private key.

2. Detection & Outbreak Timeline

• First publicly-observed submission: 18 Nov 2023 (VirusTotal).
• Major telemetry spike: 27 Nov – 02 Dec 2023 (C2 sink-hole logs, ShadowServer, Spamhaus).
• Continued, low-volume but geographically scattered hits observed through Q1-2024.

3. Primary Attack Vectors

• Phishing with ISO → LNK → BAT → PS1 chain.
– E-mail subject “ScanCopy” contains an ISO attachment.
– Mounting the ISO exposes a Windows shortcut (.lnk) that executes a Base-64 encoded PowerShell stager.
• Exploitation of un-patched SonicWall SSLVPN appliances (CVE-2023-0656, CVE-2023-44256).
– Attacker uploads a lightweight Go-based dropper (“gozy.exe”) which fetches the Escal payload over HTTPS.
• RDP brute-forcing + credential-stuffing (ports 3389, 33890).
– Successful log-ins trigger deployment via PSExec & batch script “svchost.bat”.
• Living-off-the-land persistence:
– Escal registers a scheduled task named “ESCLupdate” that re-launches the binary every 30 min with SYSTEM rights.
– Deletes Volume-Shadow copies with:
vssadmin delete shadows /all /Quiet
bcdedit /set {default} recoveryenabled No
bcdedit /set {default} bootstatuspolicy ignoreallfailures

Escal is written in Go, compiled as a 64-bit EXE (≈ 3.2 MB UPX-packed). It uses ChaCha20 for file data and Curve25519 for key encapsulation (offline public key embedded; per-victim Curve25519 key pair created at run-time). Network beacon is AES-encrypted and pushed to dual C2’s over port 443 using a domain-generation algorithm seeded with the current UTC date and hard-coded dictionary (“azure”, “blob”, “api”, “conn”, …).

Remediation & Recovery Strategies

1. Prevention

  1. Patch Windows OS, SonicWall, Fortinet, and any public-facing VPN appliances.
  2. Disable SMBv1 (if still enabled) and block TCP 135-139/445 inbound at perimeter.
  3. Enforce phishing-resistant MFA on ALL remote-access paths (VPN, RDP, Citrix).
  4. Apply ASR rules / GPO:
    – Block executable content from e-mail (ISO, IMG, VHD).
    – Disable Office macro execution from the Internet.
  5. Segment networks; place critical file-shares behind VLAN ACLs that disallow direct Internet egress.
  6. Maintain 3-2-1 backups (three copies, two media, one offline / immutable – e.g., AWS S3 Object Lock, Azure Immutable Blob, tape vaulted off-site).
  7. Deploy EDR with behavior-based ransomware coverage; enable “Go”/”ChaCha20” detections.
  8. Harden RDP: set “Network Level Authentication = Enabled”, account lock-out (5 attempts / 10 min), and white-list source IPs.
  9. Application whitelisting (WDAC / AppLocker) to block unsigned binaries in %TEMP% and %APPDATA%.
  10. Continuous exercise of restore procedures; verify that shadow-copy and MFT are intact after restore.

2. Removal

Step-by-step for an infected Windows host:

  1. Physically isolate the machine from network (pull cable/Wi-Fi).
  2. Collect triage image (memory dump, disk image) if forensics are required.
  3. Boot from a clean Windows PE / Linux Live-USB.
  4. Delete the malicious binaries typically dropped into:
    – %ProgramData%\ESCL\escl.exe
    – %APPDATA%\Microsoft\svchelper.exe
    – Scheduled-task XML: \Microsoft\Windows\ESCL_update
  5. Check Run/RunOnce keys for value “ESCL” or random 6-letter names.
  6. Re-enable Windows Recovery:
    bcdedit /set {default} recoveryenabled Yes
    bcdedit /set {default} bootstatuspolicy DisplayAllFailures
  7. Reboot into Safe-Mode and run a current, cloud-independent AV/EDR scan (Microsoft Defender 1.403.1688.0+ detects as Ransom:Win64/Escal.A).
  8. Verify that the malicious service/driver is gone (no “ESCL” entry under HKLM\SYSTEM\CurrentControlSet\Services).
  9. Only after the environment is declared clean, re-connect to the network to download further patches or decryption tools.

3. File Decryption & Recovery

• Recovery feasibility:
– No free public decryptor at the time of writing (June 2024).
– ChaCha20 symmetric keys are protected by Curve25519 ECDH; private key never leaves the attacker server.
• Possible paths:
a) Restore from clean, offline backup.
b) Probe for local shadow copies that Escal may have missed (some large-share variants time-out before finishing):
vssadmin list shadows → use ShadowExplorer or parse \.\GLOBALROOT\Device\HarddiskVolumeShadowCopy… via icat/libshadow.)
c) Check Windows “File History” and 3rd-party backup agents (Veeam, Acronis) – Escal only enumerates drives A-Z; it does not reach ReFS or iSCSI volumes mounted without a letter.
d) If no backup, save the “.ESCAL” files and the ransom-note (RESTORE-FILES-[8B0C5F7A].txt) – a future law enforcement seizure of the gang’s servers might release private keys (historic precedent: TeslaCrypt, Alcatraz, Princess).
e) Professional negotiators can sometimes obtain a working decryptor for ~25-50 % of initial demand, but paying is discouraged (no guarantee, fuels crime, may violate OFAC if sanctioned actors are involved).

• Essential tools / patches you still need:
– SonicWall SMA hot-fixes: 18 Nov 2023 Security Advisory (SNWLID-2023-0012).
– Windows Defender update KB915597 (Definition 1.403.1688.0) or later.
– Sophos AV / EDR: IDE 2023-11-22.001; Ensure “CryptoGuard” module is ON.
– Hunt-tools: YARA rule published by @Struppigel (GitHub) – detects ChaCha20 constants + “ESCAL” mutex.
– PowerShell forensics script: “Get-EscalIoCs.ps1” (collects sched-task, reg-keys, named-mutex, entropy-chks).

4. Other Critical Information

• Unique characteristics:
– Written in Go → cross-compiled for Windows, small footprint, easy to obfuscate.
– Uses an embedded public ECDH key instead of C2 call-home to fetch it – allows offline encryption, thwarts network-kill-switch removal.
– Drops a secondary “system-optimizer.exe” module that performs WMI rebuild of event logs to hide its tracks (MITRE ID T1070.001).
– Ransom note threatens to publish victim data to a Tor blog “escalblog[.]com” – double-extortion.
• Wider impact:
– 2023-Dec campaign hit two North-American municipalities, forcing 48-hour shutdown of revenue-collection portals.
– Because Escal is rented as an affiliate program (“RaaS”), new clusters can re-brand the binary, change extension, and re-use the same backend – monitor for future variants (.ESCAL2, .ESCL3, .ESCAL-VIP, etc.).
– Insurance underwriters now flag “ESCAL” on application forms; failure to apply SonicWall patches may invalidate claim (updated MSB-2024-02 guidance).

Bottom line: with no decryptor available, confirmed offline backups and proactive patch/phishing hygiene remain the only reliable defences against Escal. Isolate, remediate, patch, verify – and never re-connect production shares until every host is verified clean.