booknish

[Content by Gemini 2.5]

Technical Breakdown: Booknish Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Encrypted files receive the fixed extension .booknish appended to the original filename, separated only by the final dot of the original extension (e.g., report.xlsx.booknish).
  • Renaming Convention:
    The malware preserves the original name, extension, and directory structure; only the trailing .booknish is added. No ID prefix or double-extension tricks are used, making it visually simple for users to spot infection.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First observed in underground forums on 13-Feb-2024; aggressive mass-mail campaigns kicked off in late March 2024, with peak infection waves across Europe and North America during April–June 2024. Public reporting spiked after threat-intel firm “Shadowous” published IOCs on 02-May-2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing emails with ISO/IMG attachements – emails purport to contain a purchase order or tax refund document; the ISO mounts a hidden shortcut (.LNK) that side-loads the loader DLL.
  2. Exploitation of exposed RDP – attackers brute-force weak credentials, then deploy the ransomware via PowerShell cradle or scheduled task.
  3. Fake browser-update malvertising – poisoned search-engine ads for Chrome/Edge/Firefox deliver a MSI installer that drops the same loader.
  4. SMBv1 (especially on printers and IoT gateways) – a patched variant of the open-source “LockHost” worm module spreads laterally where SMBv1 remains enabled.
  5. CVE-2023-34362 (PaperCut NG) in print servers – remote code execution leveraged in at least three targeted organizations.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
  • Disable SMBv1 on all endpoints and servers with Disable-WindowsOptionalFeature –Online –FeatureName SMB1Protocol.
  • Require MFA for every RDP or VPN login; implement IP allow-lists for management interfaces.
  • Block ISO, IMG and VHD email attachments at the mail gateway for external senders.
  • Push Group-Policy to prevent Office macros from running in Internet-derived documents.
  • Keep browsers and plugins patched; deploy browser extension policy to forbid sideloading except from trusted source IDs.
  • Update PaperCut installations to NG version 21.2.8 or later to mitigate CVE-2023-34362.
  • Maintain offline, password-protected backups with immutability (object lock/SOC-2). Perform quarterly restore drills.

2. Removal

  • Infection Cleanup (step-by-step):
  1. Isolate the host → disconnect all NICs / VLAN or shut the guest down in hypervisor.
  2. Boot to WinRE (or live-Linux USB) to prevent the ransom binary from reloadng.
  3. Scan & eradicate:
    – Signature: use updated Windows Defender or ESET 17.2+ which detect Ransom.Booknish.A.
    – YARA rule (booknish_strats.yar) to spot hidden loader DLLs in *%APPDATA%\Skylark*.
  4. Delete persistence:
    – Scheduled Tasks: UpdateBookIndex, BookIndexScheduler.
    – Registry Run keys: HKCU\…\Run → “SkyIndexUpdate”.
  5. Validate boot environment: run sfc /scannow then chkdsk /f /r.
  6. Re-image or rebuild: for critical domain systems, fresh OS install is strongly advised.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Limited. Booknish uses AES-256 in CBC mode with separate, randomly generated keys per file; the session keys are encrypted by Curve25519 and then wiped from disk. At present, only one master decryption key (FTCRecoverykey_001.dat, released 27-Jul-2024) is known for the early campaign cluster; newer samples use different master keys.
  • Essential Tools/Patches:
    – Avast Booknish Decryptor 1.2 (works if ransom note is READMEBOOKNISH.txt and SHA-256 of locklocal.key.ini matches IOC list “booknishjul27hashset.csv”).
    – If no matching master key, restore from offline backups using 3-2-1 rule.
    – Volatility “booknish_recover.py” – reconstruct deleted metadata volumes on NTFS volumes where Shadow Copies were not erased.

4. Other Critical Information

  • Unique Characteristics:
    – Destroys Volume Shadow Copies via wmic.exe shadowcopy delete and modifies the VSS service ACL to prevent re-creation.
    – Performs file-name “quoting” before encryption: special characters are hex-encoded to avoid path truncation errors on SMB shares.
    – Sporadic errors (Unicode double-BOM) in README_BOOKNISH.txt allow analysts to fingerprint the exact build (v1.2.4 vs v1.3.1).
  • Broader Impact:
    – Over 240 public incidents tracked (HG-ISAC Ledger #24-089) since March; 30 % in education and healthcare.
    – Average ransom demand: 0.25 BTC, but negotiators report 40 % accept 60 k USD flat (H2 2024 trend).
    – Supply-chain risk: infected update package from a popular e-book reader vendor (retracted 04-May-2024) facilitated auto-install of the loader DLL.

Closing Advice:
If you discover .booknish files, preserve evidence (forensic image, RAM dump) before re-imaging—key fragments sometimes reside in hibernation or pagefile. Should no decryptor apply, engage a reputable incident-response firm; stretching negotiations beyond 14 days causes many actors to permanently delete their private key cache.