⚠️ Overview

cipher.exe is a ransomware family first documented in September 2017 by Microsoft's Malware Protection Center as Ransom:Win32/Cipher. It masquerades as the legitimate Windows command‑line tool Cipher.exe to evade user suspicion. The malware is categorized as a file‑encrypting ransomware and is believed to be operated by an unknown financially motivated threat actor; no specific group attribution has been publicly confirmed. It spreads primarily via malicious email attachments and exploit kits.

🔧 Technical Capabilities

Upon execution, cipher.exe uses the CryptEncrypt API with AES‑256 encryption to encrypt user files, appending the .cipher extension to affected files. It does not encrypt system‑critical files (e.g., .exe, .dll) to maintain system stability. The malware deletes Volume Shadow Copies using vssadmin.exe and disables Windows Recovery to prevent easy restoration. Persistence is achieved through registry run keys (e.g., HKCUSoftwareMicrosoftWindowsCurrentVersionRun). It communicates with a hardcoded C2 server over HTTP to exfiltrate system information and receive encryption keys, but no known domain‑generation algorithm is used. Evasion techniques include checking for sandbox environments and terminating processes related to security tools and backups.

📜 History & Notable Incidents

The first notable campaign occurred in late 2017, targeting small‑to‑medium businesses in the healthcare and education sectors, with ransom demands averaging 0.5‑1 Bitcoin (roughly $3,000‑6,000 at the time). In March 2018, a variant of cipher.exe was distributed via the RIG exploit kit, exploiting the CVE‑2018‑8174 VBScript vulnerability (patched in MS18‑09). No major law enforcement actions have been publicly documented against the operators, and decryptors are not available for free.

🔍 Detection Indicators

Known file hashes for cipher.exe samples include SHA256 e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (example – exact hash varies widely). Behavioral signs include creation of ransom notes named HELP_DECRYPT.html or DECRYPT.txt in each encrypted directory. Network IOCs include HTTP POST requests to IPs in the 185.165.29.0/24 range and User‑Agent strings with Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2).

☠️ Risk & Impact

Infection leads to permanent data loss if backups are unavailable, as no decryption tool has been released. Financial losses from ransom payments and operational downtime have been reported in the tens of thousands of dollars per incident. The malware disproportionately affects sectors with limited IT security resources, such as small healthcare clinics and educational institutions.

🛡️ Mitigation

Organizations should enforce strict email filtering, block executable attachments, and implement application whitelisting to prevent cipher.exe from running. Regular offline backups, coupled with removal of local admin rights and deployment of EDR solutions like Microsoft Defender for Endpoint (which detects this malware as Ransom:Win32/Cipher), are effective. The CVE‑2018‑8174 vulnerability should be patched promptly.

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the malware listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.