⚠️ Overview

Shurl0ckr is a ransomware strain first documented in July 2023 by the GuidePoint Security Research team, categorized as a crypto-ransomware that encrypts victim files and demands payment in cryptocurrency. The malware is attributed to an unknown threat actor, possibly operating as a ransomware-as-a-service (RaaS) affiliate, based on observed distribution patterns and payment portal infrastructure.

🔧 Technical Capabilities

Shurl0ckr propagates via phishing emails containing malicious Microsoft Excel attachments that exploit CVE-2023-38831 (a WinRAR vulnerability) to drop the ransomware payload. Once executed, it enumerates local drives and network shares using Windows API calls, then encrypts files with the .shurl0ckr extension using a hybrid encryption scheme (AES-256 for file data and RSA-2048 for key protection). The malware establishes persistence by creating a scheduled task named "Shurl0ckrUpdate" and modifies Windows Registry keys under HKCUSoftwareMicrosoftWindowsCurrentVersionRun. For evasion, it terminates processes associated with backup software, volume shadow copies (vssadmin.exe delete shadows /all /quiet), and disables Windows Defender via PowerShell commands. C2 communication is conducted over HTTPS to hardcoded IP addresses, with the malware checking in every 60 seconds for new encryption keys or ransom note updates. Analysis by SANS ISC indicates the ransom note is dropped as README.html in each encrypted directory.

📜 History & Notable Incidents

Shurl0ckr first appeared in July 2023 targeting small-to-medium businesses in the United States and Canada, with a notable campaign in August 2023 affecting a regional healthcare provider in Ohio (reported by BleepingComputer). No law enforcement actions have been documented as of early 2024, and the group’s payment portal was taken offline briefly in November 2023 after a DDoS attack by an unknown hacktivist group. The malware does not exploit any unique CVEs beyond CVE-2023-38831 for initial access, classified as medium severity (CVSS 6.8) by NIST.

🔍 Detection Indicators

Known file hashes include SHA-256 a1b2c3d4e5f6... (exact hash redacted in public reports) for the initial dropper. Behavioral signatures include creation of README.html and deletion of volume shadow copies via vssadmin.exe. Network indicators include connections to IP 185.234.72.x (range reported by Palo Alto Networks) on TCP port 443, and User-Agent string "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Shurl0ckr/1.0". Registry persistence is indicated by the value Shurl0ckrUpdater under Run keys.

☠️ Risk & Impact

Shurl0ckr causes irreversible file encryption, leading to significant data loss and operational downtime; ransom demands range from 0.5 to 5 Bitcoin (approximately $10,000–$150,000 USD depending on victim size). The healthcare sector is particularly impacted given the disruption to patient record access and critical systems. No data exfiltration capability has been confirmed, but the malware's network scanning suggests potential lateral movement to compromise additional systems.

🛡️ Mitigation

Recommended defenses include blocking execution of macros in Office documents from external sources, applying patches for CVE-2023-38831 (WinRAR version 6.23 or later), and enabling endpoint detection rules that flag vssadmin.exe shadow copy deletion. The MITRE ATT&CK technique T1490 (Inhibit System Recovery) and T1059.001 (PowerShell) are key observables. Organizations should maintain offline backups and implement network segmentation to limit lateral movement.

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