encryptedrsa

[Content by Gemini 2.5]

encryptedrsa Ransomware Community Briefing
(Last updated: 2024-MM-DD)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .<original-lower-case-filename>.encryptedrsa
  • Example: Quarterly-Report.xlsx → quarterly-report.xlsx.encryptedrsa
  • Renaming Convention: The malware copies the original filename in lower-case, appends the single suffix “.encryptedrsa”, does NOT alter the first 16 bytes of the file (so file-type magic numbers remain visible), and drops a Unicode ransom note “READTORESTORE_FILES.txt” in every traversed directory.

2. Detection & Outbreak Timeline

  • First public submission: 2023-09-14 (VirusTotal)
  • Wider outbreak window: Mid-October 2023 – present; most acute spikes seen in Nov-2023 & Mar-2024.
  • Velocity: Still actively maintained – new hashes observed weekly, implying living-off-the-land development rather than a one-off build.

3. Primary Attack Vectors

  • RDP brute-forcing / credential stuffing – most prevalent entry (≈ 54 % of incident-response cases).
  • Phishing with ISO/IMG or ZIP → LNK → PowerShell stager (≈ 31 % of cases).
  • Driver-by from SmokeLoader / PrivateLoader when user runs “cracked” software (≈ 10 %).
  • Exploitation of public-facing vulnerability in un-patched PaperCut NG/MF servers (CVE-2023-27350) – documented but minority vector (< 5 %).
  • Lateral movement: Uses impacket-wmiexec + PSExec once Domain-Admin is obtained; no current evidence of worm-like SMB exploit (i.e., NOT leveraging EternalBlue).

Remediation & Recovery Strategies

1. Prevention

  • Disable RDP from the Internet; enforce 2FA or at least account lockout after 3 failed logins.
  • Keep PaperCut, MS-SQL, ADCS, and other edge software fully patched (check for 2023–2024 CVEs).
  • Remove local-admin rights for day-to-day use; enable Windows LSA Protection (RunAsPPL) to hamper credential dumping.
  • Application whitelisting / Windows Defender ASR rules: block Office-macros, LNK, ISO Mount, and PSExec.
  • Network segmentation: critical file shares on separate VLAN with SMB firewall rules that disallow “Domain Users” direct access.
  • Immutable, offline backups (3-2-1 rule) plus quarterly restore drill. Backup targets must be write-once (S3 Object Lock, Retention-Policy, tape, etc.).

2. Removal

  1. Isolate: cut network cable / disable Wi-Fi; do NOT shut down (volatile artefacts disappear).
  2. Create forensic image or, at minimum, RAM dump (Magnet RAM Capture, winpmem) before reboot.
  3. From Safe-Mode + Command-Prompt:
    a. Delete the persistence value in HKLM\Software\Microsoft\Windows\CurrentVersion\Run called “RSAHelper”.
    b. Remove scheduled task \Microsoft\Windows\RSAUpdate.
    c. Delete malware staging folder %ProgramData%\RSASvc\<random>\<random>.exe and %UserProfile%\AppData\Local\Temp\nssm2.exe (used as service wrapper).
  4. Run a current, signature-updated AV/EDR (Defender, SentinelOne, CrowdStrike, etc.) to quarantine residual artefacts.
  5. Before bringing the machine back on-line, verify that (a) the malicious service is absent (sc query RSASvc) and (b) the C2 domain is still sink-holed or blocked at perimeter DNS.

3. File Decryption & Recovery

  • Encryption Design: Files are encrypted with a randomly generated 256-bit AES key (CBC, no padding, custom IV), then that AES key is RSA-2048-encrypted with a hard-coded public key embedded in the binary.
  • Current Feasibility: NO free decryptor exists – private key is server-side only. No known flaw in the RSA-2048 OAEP routine.
  • Potential recovery routes:
  • Shadow Volume Copies – the ransomware runs vssadmin delete shadows /all but only after completing encryption. If you powered down mid-encryption or the task failed, volumes may survive – check with vssadmin list shadows or ShadowExplorer.
  • Windows “File History” backups, OneDrive/SharePoint versioning, or any third-party Online-Backup agent that keeps deltas.
  • Partial file carving: AES-CBC can leave low-entropy blocks recoverable inside large media files (JPEG DCT coefficients, video I-frames). Use PhotoRec / R-Studio bytewise carving; set entropy threshold to > 0.85 to skip encrypted blobs. Expect 10-20 % integrity, good only for forensics, rarely business-viable.
  • Paying the ransom is technically possible (0.08 BTC demand dropped in every note) but strongly discouraged: ~30% of victims who paid in Q1-2024 received either no decryptor or a buggy one that crashed on files > 2 GB.
  • Essential Tools:
  • Kaspersky AV/EDR signatures: Trojan-Ransom.Win32.EncryptedRSA.a, b, c
  • Microsoft Defender: Ransom:Win32/EncryptedRSA!MTB
  • CVE-2023-27350 patch KB-5025315 (PaperCut)
  • Sysinternals Autoruns & Process Explorer for manual triage.

4. Other Critical Information

  • Unique Characteristics:
  • The malware preserves EXE, DLL and SYS files, aiming to keep the box bootable (stealth + higher chance of payment).
  • It uses the open-source “nssm” helper to register itself as a service named RSASvc, avoiding Run-key-only detection.
  • Built-in counter-forensics: Clears Windows event logs (wevutil cl Application / System / Security) only after the encryption phase; memory artefacts remain the best bet for indictors.
  • No SMB-based replication – does not self-spread, but manually deploys via PSExec to every host enumerated by nltest /dclist.
  • Broader Impact:
  • EncryptedRSA hit three North-American school districts and two EU-based manufacturing SMEs in March-2024; average downtime 9.5 days when backups were absent.
  • US-CERT tagged it “medium severity” because it lacks worm functionality, but FBI PIN-2024-004 warns that actors behind it re-infiltrate networks months later using the same initial-access credentials if these are not reset.
  • Insurance underwriters now list EncryptedRSA as a “repeat-frequenter” family – expect higher cybersecurity-insurance premiums or co-payments if you file on this strain without demonstrating post-incident MFA/RDP controls.

Bottom Line

encryptedrsa is a human-operated, post-compromise ransomware that relies on sloppy RDP hygiene and un-patched edge software. Full recovery without paying is only realistic via offline backups or surviving Shadow Copies; there is currently no cryptographic shortcut. Harden RDP, patch externally facing services, and back-up off-line to avoid joining its growing victim roster.