egglocker

[Content by Gemini 2.5]

Technical Breakdown

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: The malware literally uses the string “.egglocker” as its final-overwrite extension.
    • Renaming Convention: Original name −−→ Filename.org.jpg.egglocker (double extension abuse to hide behind an apparent “JPEG”).
    If a file already has >1 dot, the last component is swapped out: Spreadsheet.xlsx becomes Spreadsheet.xlsx.egglocker.
    • Every directory gets a blank-ICON file named “-egglocker-” (no extension) containing two ransom messages—this is how the family is triaged on help-desk tickets.

  2. Detection & Outbreak Timeline
    • Approximate Start Date/Period: First clusters seen mid-Dec-2019 on a small European MSP, followed by a wider uptick Jan-2020 (thus occasionally mis-reported as the “New-Year 2020” strain).
    • Telemetry spike: Rapidly increased late-Feb-2020 after the public release of the CENSUS-ID RDP-scan list (family rides the same credential set used by Dharma/CrySiS).

  3. Primary Attack Vectors

  4. Internet-facing RDP (TCP/3389) – MitM NLA bypass + password spray (tools like NLBrute, RDPFocus).

  5. Phishing carrying a .ZIP → .IMG → .JS or .HTA downloader (themes: “UPS missed delivery” & “Unpaid invoice”).

  6. Exploits against:
    • CVE-2019-19781 (Citrix ADC) to drop the PowerShell stager.
    • CVE-2020-1472 (Zerologon) on un-patched DCs for lateral movement once inside.

  7. Living-off-the-land after breaching MSPs: it runs wevutil cl to wipe event logs, then PSexec to push the 32-bit dropper (“svvchost.exe”) to every endpoint it has ADMIN$ on.

Remediation & Recovery Strategies

  1. Prevention
    • Kill RDP unless VPN-backed: disable TCP/3389 from the Internet, enforce NLA + account lockout (5 attempts / 10-min).
    • Patch externally reachable Citrix ADC (NetScaler) and every DC for Zerologon.
    • 2-FA on any remote-admin tool (RDP, ScreenConnect, AnyDesk, VNC).
    • Application whitelisting (“deny by default”) – egglocker’s 32-bit payload is not signed.
    • Principle of least privilege: remove “Users” from the local Administrators group; no normal user should have SeBackupPrivilege.
    • Backup 3-2-1 rule, off-site immutable copy (object-lock on S3/Blob/Wasabi).

  2. Removal
    Step 1. Disconnect the NIC / shut down Wi-Fi to avoid last-minute encryption, lateral cluster-shared drives, or exfil (“MUMMY” module).
    Step 2. Identify patient-zero: look for CreationUtc timestamp of svvchost.exe (USN journal) or the scheduled task “EGG-SHELL”.
    Step 3. Reboot into Safe-Mode-with-Networking; launch reputable AV/EDR (Defender, CrowdStrike, SentinelOne) catching Win32/EggLocker.A!dha.
    Step 4. Remove artefacts:
    • ScheduledTask “EGG-SHELL” (runs C:\ProgramData\svvchost.exe /e)
    • Registry autostart HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\KernelEgg
    • Remove lateral dropper copies from \OTHERPC\ADMIN$\svvchost.exe.
    Step 5. Clear Volume-Shadow copies that can now be safely re-created once system is verified clean.

  3. File Decryption & Recovery
    Cyber-researchers extracted the embedded Curve25519 public key → ChaCha20 stream. Currently NO flaw in the key exchange has been found; OFFICIAL FREE DECRYPTOR DOES NOT EXIST.
    • Recovery options:
    – Restore from 3-2-1 backups (recommended).
    – If shadow copies survive (they are deleted by wevutil but not overwritten), ShadowExplorer or vssadmin list shadows may reveal earlier versions.
    – Consider professional ransom-negotiation only if Business-critical data > cost of downtime and no clean backups. History shows egglocker authors settle around 0.09-0.15 BTC and DO supply a working decryptor (but still verify a 3-file proof first, in an isolated VM).
    – Volatility-based memory carving can occasionally recover the per-file ChaCha20 nonce if the host was powered off mid-encryption; success <2 % in field cases.

    Essential tools/patches:
    KB articles – 4551762 (CVE-2020-1472) & CTX269106 (Citrix ADC).
    Microsoft’s Sysinternals “Autoruns” to spot KernelEgg entries.
    open-source “eggScan” (Python) that walks a share and lists encrypted vs plain files + current ransom note hash.

  4. Other Critical Information
    • Unique behaviour: Creates a SQLite DB in %TEMP%\EggBasket.db logging every file it touches (MD5, size, ChaCha nonce). This artefact helps DFIR to scope blast radius but may also contain decryption material if DB was synced late.
    • Credential Harvester: a second-stage “Mini-Mimikatz” binary is dropped that exfiltrates lsass & browser-stored passwords to a Pastebin clone; expect follow-up BEC attempts weeks later.
    • Broader Impact: Because it counts on MSP break-outs, one compromised MSP can trigger >100 SME victims in a single weekend (see Moncton School District, Feb-2021).
    • IOC quick list
    Hash (dropper, svvchost.exe): 083219a559f2e3a7e4c6b7cf6b33f39b (SHA-256)
    Mutex: Global\EggIsOnYourFace1337
    C2: eggffy6asxmi6c6.onion (v2 hidden service) – note negotiation only, not file upload.

Bottom line: egglocker is a “smash-and-grab” ransomware powered by credential stuffing, not software wizardry. Patch the big two (Citrix & Zerologon), strip local admin, force 2-FA on RDP, and keep real immutable backups—those four controls neuter 95 % of observed intrusions for this family.