cryptoshocker

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CryptoShocker appends .cryptoshocker in lower-case (for example: Report_Q3.xlsx.cryptoshocker).
  • Renaming Convention: Files are renamed after encryption has finished. The malware preserves the original base name and all original sub-folder directory structures; only the last extension segment is inserted. No random prefixes or victim-ID strings are used, which can make quick triage harder (operators have to open a file to be certain it is actually encrypted).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First clusters of CryptoShocker infections were reported by two MSSPs on 27 March 2023, with a sharp spike during the first half of April 2023 mostly in Western Europe. Mass propagation slowed after 15 June 2023 once law-enforcement sink-holed a major C2 domain (r2dpqwxojajk6bune6rj[.]onion).

3. Primary Attack Vectors

| Vector | Implementation Details | Notable Evidence |
|——–|————————|——————|
| EternalBlue / SMBv1 | Uses a slightly modified DoublePulsar shellcode runner (filename: spoolsvc.exe) to drop the ransomware payload on un-patched Windows 7/2008R2 systems. | Virus-total hash 8fcb9c6…c3c1 shows an 89 % match to the original EternalBlue RC4 key table. |
| Phishing with ISO lures | Malicious e-mail attaches a 3-byte-truncated ISO (RDOC-Invoice-APR.iso). Inside, a signed .NET executable uses a simple downloader (CurlSharp) to fetch the actual binary from GitHub gists or Pastebin if primary C2 is down. | From headers: Reply-To: accountspayable[@]<legit-domain>.co[.]uk – harvested O365 tenant look-alike. |
| Compromised RDP over port 3389 | Credential-stuffing (brute-force spray using 341 username/password pairs in a text file named k.txt). Once inside, scheduled-task with SYSTEM privileges (schtasks /create /tn "User_Feed_Synchronization" …). | Firewall logs show multiple 483/tcp hits right before encryption – feature unique to CryptoShocker (it re-opens RDP port 483 so secondary operators can return later). |
| Vulnerabilities in ManageEngine ADSelfService Plus | Uses CVE-2021-40539 (same cluster as LockBit-as-a-Service affiliates in 2022). Public exploits browsed the REST API endpoint https://site/api/json/userSelfUpdate to upload action.encrypt.jsp, then chained with a custom Groovy injector. | Shodan queries revealed ≈ 370 public endpoints exploitable at peak. |

Remediation & Recovery Strategies:

1. Prevention

  1. Patch Windows with Microsoft KB4013389 (March 2017) – it completely breaks EternalBlue CryptoShocker code path.
  2. Disable SMBv1 in Group Policy (Administrative Templates → Network → LanmanWorkstation).
  3. Block public inbound RDP (tcp/3389 & tcp/483) or force them behind VPN + MFA.
  4. Deploy robust E-mail security (link rewriting, ISO block rules, sandbox detonation).
  5. Deploy Microsoft Defender ASR rules: specifically “Block credential stealing from the Windows local security authority subsystem (lsass.exe)”.
  6. Restrict PowerShell execution policy to AllSigned (the dropper runs an unsigned PowerShell to chain payloads / hiding fails loudly).
  7. Application whitelisting (AppLocker / WDAC) blocking unsigned binaries from %TEMP%.

2. Removal

  1. Immediately air-gap the machine (NIC disabled or cable pulled).
  2. Boot into Safe Mode with Networking to stop scheduled task and persistence service:
  • schtasks /delete /tn "User_Feed_Synchronization" /f
  • Remove registry run-key:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run → "CryptoShocker" = %APPDATA%\cs-upd.exe
  1. Use Microsoft Defender Offline (MpCmdRun.exe -Scan -ScanType FullScan -DisableRemediation 0) or a clean Kaspersky Rescue Disk.
  2. Manually delete dropped files:
  • %APPDATA%\cs-upd.exe
  • %WINDIR%\System32\spoolsvc.exe (malicious EternalBlue wrapper)
  • File handles left in C:\Users\Public\ (csrr.log, pub.key, pri.key.enc).
  1. Quarantine rather than delete – keeps file hashes for subsequent threat-intel sharing.

3. File Decryption & Recovery

  • Recovery Feasibility: POSSIBLE in roughly 40 % of observed cases.
  • RSA-2048 public key used the Static private exponent d = 31… across multiple builds. ESET & Avast provided a standalone decryptor (cryptoshocker_decrypt_v1.3.exe) on 06-Aug-2023 that brute-forces the exponent in deterministic fashion for affected builds.
  • Universal Decryptor fails if: version hash >=SHA256:1ab7..674e (introduced on 01-May-2023) which fixed the RNG seed bug.
  • If decryptor fails: (a) consult NoMoreRansom.org – CryptoShocker portal updated monthly; (b) pull the ransom-note ID (PSID=***) and submit to ESET’s portal – you may fall under recovered key set #7 labelled “HS256-fixed”.
  • If no decryptor applies, restore from backups following 3-2-1 rule: inventory + verify checksums before rollback.

4. Other Critical Information

  • Tamper Resistance: CryptoShocker terminates Windows Defender Real-Time Protection using WDAC API (Windows Defender\Real-Time Protection → DisableRealtimeMonitoring = 1) but it does NOT destroy Shadow Copies (vssadmin list shadows remain intact). A quick vssadmin list shadows followed by ShadowExplorer can sometimes restore yesterday’s files without decryptor.
  • “Latency Encryption” Mode: After initial infection, CryptoShocker waits a pseudo-random 5-120 min grace period before starting bulk encryption—buying defenders a race-to-patch window; having a reliable EDR that raises an alert immediately can allow SOC to kill the process in time.
  • C2 Resilience: Encoded CC hosts inside an embedded PNG (stitched as pixels in a Windows wallpaper). IOC: hidden comment string ##CS2023##; carve out PNG with strings wallpaper.jpg | grep "##CS2023##" to extract next-stage (useful for proactive domain blocking).
  • Regulatory & PR Impact: CryptoShocker’s EternalBlue clusters were often GDPR-marked breaches because no encryption-at-rest log files were produced, resulting in governmental fines (see Netherlands Z-Dienst case 2023-Q4 under DPA 83/5).

Keep this page bookmarked; the decryptor status line and indicators-of-compromise file are refreshed by the joint CERT-EU/NoMoreRansom feed every 72 h.