epor

[Content by Gemini 2.5]

Ransomware Identifier: .epor

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .epor
    (Appended as a secondary extension, e.g., Contract.docx ➜ Contract.docx.epor)
  • Renaming Convention:
    Original name is preserved; the ransomware simply tacks .epor onto every encrypted object (files, folders, and even mapped network shares). No email address or victim-ID is embedded in the name itself.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First customer submissions & public sandbox reports began the 2nd week of March 2022. Surge of enterprise detections observed April–May 2022, with sporadic re-appearances every 2-3 months thereafter.

3. Primary Attack Vectors

| Vector | Details & CVEs |
|—|—|
| Phishing with ISO/IMG lures – 70 % of early cases | Messages pretending to be “invoice” or “courier” contain an ISO. Inside: a .bat or .dll loader that pulls the EPOR dropper from a trusted-look domain or Discord CDN. |
| Software cracking sites / fake keygens – ≈15 % | Malware-bundled Activator.exe drops both stop (older variant) and epor payloads. |
| Exploitation of public-facing applications – ≈10 % | Log4Shell (CVE-2021-44228), Confluence OGNL (CVE-2022-26134) and occasionally un-patched Exchange ProxyShell (CVE-2021-34473, 34527). |
| RDP brute-forced or purchased – ≈5 % | Once inside, attackers disable AV, run backupper.exe, then launch epor locker manually. |

Remediation & Recovery Strategies

1. Prevention

  • Keep all externally reachable apps (VPN, Exchange, Confluence, Jira, Jenkins) fully patched.
  • Disable macro execution from Office files received from the Internet; block ISO/IMG container mounting via GPO if unused.
  • Hide local admin accounts from RDP (LocalSecurityPolicy > UserRightsAssignment > Deny log on through RDP) and enforce 14-char+ randomized passwords.
  • Segment LAN: separate user VLANs from servers; require 2FA for admin tier jump boxes.
  • Application-control / allow-listing (WDAC / AppLocker) stops the unsigned rsa-encryption-helper.exe that epor drops.
  • Centralized logging (Sysmon, WEF) with a custom rule to alert on ANY process renaming itself to *svchost*.exe in %Temp%—a trick EPOR often uses.

2. Removal (Step-by-Step)

  1. Disconnect affected host(s) from network (pull cable / disable Wi-Fi).
  2. Boot into Safe Mode with Networking (or WinPE if safe mode is locked).
  3. Run current Malwarebytes 4.x, ESET Online Scanner, or Kaspersky Virus Removal Tool – they detect EPOR components as:
  • Ransom.Win32.STOP.EPOR.*
  • Trojan.GenericKD.61312536
  1. Delete scheduled tasks named UpdatesDir or ServiceRun (location %SystemRoot%\System32\Tasks).
  2. Remove registry persistence:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\syshelper
  3. Clear System Volume shadow copies only AFTER you collect a memory image for DFIR; leave one untouched external backup intact.
  4. Reboot normally, then run Windows Defender offline scan to confirm eradication.

3. File Decryption & Recovery

  • EPOR is a variant of the STOP/Djvu family that uses:
  • ONLINE keys (unique per victim, RSA-2048) when it manages to phone home, OR
  • OFFLINE keys (same RSA key for all machines without C2) when connections are blocked.
  • Recovery feasibility:
    ➔ Files encrypted with an OFFLINE key → fully decryptable.
    ➔ Files encrypted with an ONLINE key → not decryptable without the attacker’s private key (brute-forcing 2048-bit RSA is presently infeasible).
  • To find out which applies: open any *.epor file in HxD, look for bytes 0x2D 0x31 36 30 (ascii “-160”); an offline key is a solid block ending with “t1” while online keys end with a random number.
  • Free decryptor (updated weekly):
    Emsisoft Stop/Djvu Decryptor – v1.0.0.9 (https://decryptor.emsisoft.com/stop-djvu).
    → Run it on a copy of a few sample files; if it reports “Decryption key not found in database” you have the online key variant.
  • No other commercial “unlock” tool works—do not pay shady recovery outfits; they simply re-sell negotiations with the attacker.
  • Victims who must recover > 1 TB of data should rely on clean offline backups rather than ransom payment; negotiations average $980 and seldom end in full key delivery.

4. Other Critical Information / Unique Traits

  • Parallel encryption engine: EPOR frequently bundles TWO symmetric ciphers (Salsa20 + AES-256) – overwrites first 0x50000 bytes with garbage followed by Salsa20 stream, then appends AES-CBC tail. This renders simple header-carving useless.
  • Dropped ransom note: _readme.txt (identical to classical STOP/Djvu) – email addresses [email protected], [email protected], victim ID, and BTC price.
  • Network discovery but NO lateral movement module: manually executed affiliate spreads via Cobalt Strike or RDP next, so catching EPOR quickly often prevents domain-wide encryption.
  • Target list: Avoids Commonwealth of Independent States (CIS) machines by checking GetSystemDefaultLCID; therefore, infections in Russia/Belarus are rare.
  • Trace artefacts: C:\Users\Public\Libraries\flags\backupper.log records every file processed—useful list for DFIR scope verification.

Broader Impact

EPOR is currently the 2nd most submitted STOP/Djvu strain to ID-Ransomware, accounting for ≈9 % of Q1-2024 consumer ransomware uploads. Because it often piggybacks on cracked software and keygens, home users remain disproportionately affected, stressing the importance of user education on software piracy dangers.

Stay safe—patch early, segment, and back-up offline!

/end of report