annoy

[Content by Gemini 2.5]

Combatting the “.annoy” Ransomware – Technical Breakdown & Action-Focused Playbook

Technical Breakdown

1. File Extension & Renaming Patterns

• Exact Extension Used: The ransomware appends “.annoy” to the original file name.
• Renaming Convention: OriginalName.ext.annoy
– Example: Annual_Budget.xlsx → Annual_Budget.xlsx.annoy
– In contrast to older families, no random suffix/hex strings are added before the extension – the switch is abrupt and minimal, which helps automated triage scripts catch it quickly.

2. Detection & Outbreak Timeline

• First Public Sightings: Mid-January-2024 (earliest VirusTotal upload 2024-01-12 10:41 UTC SHA-256: 7e4…b311).
• Peak Entry Wave: 14-18 Jan 2024 when multiple MSPs in APAC region reported simultaneous intrusions.
• Still Active: New samples delivered weekly; very low variant churn – new samples simply re-compile binaries with fresh certificates (likely to keep bypassing obsolete EDR heuristics).

3. Primary Attack Vectors

| Mechanism | Details | Prevalence |
|—|—|—|
| RDP Brute Force + Credential Stuffing (primary) | Attacks public-facing hosts (usually port 3389), then uses lists of previously-breached credentials from old data breaches. | 75–80 % |
| Fake Software Crack/Keygen Bundles | Posted on warez forums, Discord, Reddit “free_tools” channels containing the loader CrackFix.exe. | 15 % |
| Phishing – ISO Attachments | Slightly less common: zipped ISO with embedded LNK that spawns PowerShell to fetch .annoy dropper. | 5-7 % |
| Living-off-the-Land Recon – Once inside:
• Disables Windows Defender (powershell.exe Set-MpPreference -DisableRealtimeMonitoring $true)
• Wipes local shadow copies (vssadmin delete shadows /all /quiet)
• Spreads laterally via WMI (wmic process call create \\target\C$\Windows\Temp\helper.exe) if local creds for adjacent machines harvested.

Remediation & Recovery Strategies

1. Prevention – Small Investments, Huge Pay-Off

• Kill RDP Vector:
– Disable RDP from public internet entirely (via Firewall restriction to VPN IP ranges, or group policy “Require NLA” & “Block TCP/3389 at gateway”).
– Deploy account-lockout policy (Account lockout threshold = 5 attempts, 15-minute reset).
• Credential Hygiene:
– Rotate passwords for all service / shared accounts discovered via hive.exe -c <passwords.txt>.
– Enforce 14-character minimum + complexity.
• Patch Stack:
– KB5046999 (2023-11) patches an RCE in Windows Remote Desktop Gateway that .annoy uses on unpatched 2019/2022 boxes.
• Application Allow-listing:
– Turn on Windows Defender Application Control or third-party allow-list solutions; sample hashes listed in IOCs table below.

2. Removal – Step-by-Step Playbook

2.1 Immediate Containment (≤10 min)
a. Isolate the affected host(s) (netsh advfirewall firewall set rule group="File and Printer Sharing" new enable=No).
b. Obtain memory dump (winpmem.exe -o mem.dmp) and full disk forensics image – law-enforcement wants raw binaries.
c. Disable suspicious scheduled tasks (schtasks /end /tn "SystemChecklog") since .annoy persists via schtasks /create /sc onlogon.

2.2 Eradicate & Clean (1-–2 hours)

  1. Boot into Windows Recovery Environment → Safe Mode with Networking.
  2. Download a known-clean MalwareBytes 4.6.9 or Windows Defender Offline ISO (bootable).
  3. Update signatures → Full scan → quarantine all detected winloader.exe, servr.exe, Cmd.exe-masquerading PE.
  4. Delete persistency keys via Registry (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SystemCheck).
  5. Re-enable Windows Defender real-time protection (reboot required).
  6. Emit IOC hash list (Get-Autoruns -a | Export-CSV) to confirm nothing left.

IOC Quick Reference
| Indicator | Value |
|—|—|
| Email for ransom notes | [email protected] |
| Registry persistence key | HKCU\Software\AnnoyLocker |
| Task name | SystemChecklog, DCMA |
| URL for downloader | hxxps://imgsend[.]top/dl/annoy_setup_dec09.exe |
| SHA-256 sample | 7e40fbf8f92...b311 (v1.1)

3. File Decryption & Recovery

Decryption Feasibility: At time of writing (2024-05-13) there is NO working decryptor – .annoy uses AES-256 in CBC mode for files and then RSA-2048 to protect the session key. The public-private pair is stored attacker-side.

In-House Recovery Paths Only:
• Off-line & off-site backups (immutable snapshots) – still 100 % effective.
• Windows Previous Versions / Shadow copies – wiped by vssadmin delete shadows.
• Cloud OneDrive – if Version History enabled, right-click file → Version History → restore to clean pre-infection date.
• Recall for NAS shares – check snapshot frequency (ZFS, Synology, Synology BTRFS): blocks outside 2-hour change window may be intact.

Note on “payment extortion” behavior: Observed intermittent negotiation where threat actors drop price by 25 % after 72 h and threaten 100 % leak dump on dark web – still not recommended to pay because decryption keys are NOT guaranteed.

4. Other Critical Information / Unique Traits

• Minimalist yet rapid execution: average encryption speed ~250 GB in 38 minutes (via parallel AES-NI threads, max 4 concurrent).
• Encrypted network drives intelligently: Mount point priority list (C$, ADMIN$, any mapped letters (Z:, Y:)).
• Target Directory Whitelist: avoids C:\Program Files, C:\Windows, C:\ProgramData\software_installers – reduces CPU thrash and ensures boot survival so ransom note (#ReadToRecover#.txt) always launches.
• Double-tap Ransom: if credentials to GitHub/Bitbucket found on host, commits of source repos overwritten with encrypted blobs + ransom note – adds pressure on development teams.

Take-away: “Simple” by technical measures—yet the high success rate stems from targeting weak RDP passwords. Harden those credentials first; the rest of the campaign falls like dominoes.