encrypted_rsa

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Each encrypted file simply receives the extra suffix “.encrypted_rsa” after the original extension.
    Example: Budget2024.xlsx.encrypted_rsa
  • Renaming Convention: The malware preserves the original file name (no base-64 or random ID) and converts every extension in a recursive folder crawl, so administrators can quickly identify the scope by sorting on “.encrypted_rsa”.

2. Detection & Outbreak Timeline

  • First-cluster sightings: Late January-2022 (multiple uploads to ID-Ransomware and Hybrid-Analysis).
  • Wider distribution: February-2022, when the group added Verbose-encrypted exfiltration features and the “#_HOWTODECRYPT.txt” note (later releases appended “rsa“ to the readme).
  • Last major refresh: Observed decryptor v1.6 in March-2023, indicating the payload is still being maintained.

3. Primary Attack Vectors (as confirmed by incident-response reports)

  1. Exposed RDP (TCP/3389, 33890, 3391) – brute-force of weak AD credentials, then privilege escalation via PrintSpooler or Zerologon.
  2. Phishing – ISO or IMG container attached to “invoice / job-application” themes; the image mounts a .NET loader that pulls either Cobalt Strike or a Meterpreter shell, staging “encrypted_rsa.exe“ from a CDN.
  3. Exploit of un-patched public-facing software – Atlassian Confluence (CVE-2022-26134) and Log4j2 (CVE-2021-44228). The bash or PowerShell dropper writes %temp%\svchostx64.exe which is the x64 variant of the ransomware.
  4. Software supply-chain infection – file; only one recorded case (April-2022), but the code-signing cert was revoked in May-2022.

Remediation & Recovery Strategies

1. Prevention

  • Remove or shield RDP with VPN-only access, enable NLA, enforce 14-character plus unique passwords, deploy IP-based lockout (5 bad attempts / 60 min).
  • Patch obsessively: the gang abuses one-year-old n-days, so anything later than 90 d gives them a green light. Priority list: Confluence, Log4j2, Exchange ProxyShell, Print Spooler, MSHTML, and FortiOS SSL-VPN.
  • Disable macro execution from internet-sourced Office documents – use Microsoft ASR rules or Group Policy.
  • Turn on Windows Defender AMSI signatures (up-to-date since Defender 1.379.1253 April-2022 can block the main loader).
  • Application-allow-listing (WDAC/AppLocker). Running userland binaries from %temp% or %appdata% should be denied by default.
  • Network segmentation & lateral-movement firewall rings – the ransomware asks the subnet for SMB shares; breaking broadcast domains hurts its speed.

2. Removal (Step-by-Step)

  1. Power off the affected subnet switch ports to stop encryption: the process handles up to 4 files in parallel; every extra minute costs data.
  2. Boot one clean asset from a Windows PE / Linux live-USB with up-to-date AV definitions:
    a. Rename the service executable (typical locations): C:\ProgramData\Oracle\Java\javaw.exe or %temp%\svchost*.exe.
    b. Remove the run key HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SvcHostX (random number).
    c. Delete scheduled task “JavaUpdateTaskMachineUA“ – the AES key wipe stage is triggered from here at reboot.
  3. Scan the whole disk with an offline AV engine (Kaspersky Rescue Disk/ESET SysRescue). Expect detections such as “Trojan-Ransom.Win32.Encrsa.*“.
  4. Re-image at least the OS partition; the gang also drops rudimentary backdoors (Mimikatz, Rubeus) so a bare-metal refresh is safer.

3. File Decryption & Recovery

  • No known flaw in the RSA-2040 + AES-256-CBC implementation means files are NOT decryptable without the private key.
  • Free decryptor? No. This family does not use offline keys; each victim gets a unique RSA key pair generated on the criminal server, so no universal decryptor exists.
  • Attempts to “brute the RSA private key” are mathematically infeasible.
  • Recovery paths:
    ☑ Offline / cloud backups that showed no lateral access.
    ☑ Shadow copies are deliberately purged (vssadmin delete shadows /all) – check whether the attacker failed on non-C:-volumes.
    ☑ Volume-repair tools (Photorec, R-Studio) can reconstruct some file types from un-encrypted slack space on HDDs if encryption was interrupted.
  • Paid-decrypt caveat: Victims who paid the original 0.04 BTC demand (Feb-2022) routinely received working 32-bit decryptors; however, the March-2023 variant demands 0.08 BTC and communication frequently stalls after payment.
  • Essential updates: Deploy Microsoft patches up to at least March-2023 cumulative, install the “Ransomware protection” module in Windows Security (controlled-folder access) and the Kaspersky anti-encryptor driver (free).

4. Other Critical Information

  • Post-exfil: The sample steals interesting folders (Finance, HR, Legal, PDF) first to mega[.]nz before starting encryption. Assume breach-of-data regulations (GDPR, HIPAA etc.).
  • Persistence marker: A hidden file C:.ransrv_.lck shows the date-time of first run and the affiliate-ID; useful for Digital-forensics reconstruction.
  • Language-agnostic: the ransom note “#_HOWTO_DECRYPT.txt“ is dropped in 39 languages – an uncommon feature among small families.
  • Kill-date is absent; samples keep working indefinitely, so partial rebuilds will be re-encrypted if the operator returns weeks later.
  • Because the extension is generic English, many AV engines flag it as “Possible-Ransom:Generic.RSA”. Always submit the HOW-TO note AND the executable to ID-Ransomware or VirusTotal to distinguish between copy-cats and the genuine article.

Above all, maintain segmented, offline, version-controlled backups. encrypted_rsa is beatable only through preparation – once files are encrypted the only certain antidote is restoring from backups, not paying. Stay patched, stay segmented, and keep at least one immutable copy of your data beyond the reach of affiliate hands.