Cephalus Ransomware Breaks In via RDP, Then Exfiltrates

A new ransomware operation, Cephalus, broke into organizations by weaponizing stolen or weak Remote Desktop Protocol (RDP) credentials. Because exposed RDP remains a soft target, the operators authenticated quietly, staged tooling, then executed double-extortion with tailored payloads. Consequently, victims faced encryption and data-leak pressure in quick succession.

𝗢𝗽𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝗮𝗹 𝗼𝗿𝗱𝗲𝗿 𝗼𝗳 𝗮𝘁𝘁𝗮𝗰𝗸 — 𝙄𝙉𝙄𝙏𝙄𝘼𝙇 𝘼𝘾𝘾𝙀𝙎𝙎 → 𝙀𝙓𝙁𝙄𝙇 → 𝙀𝙉𝘾𝙍𝙔𝙋𝙏

Operators authenticated over RDP, enumerated the environment, and moved with intent. Then, they exfiltrated sensitive data to external file-sharing and leak infrastructure. Afterwards, they launched encryption designed to maximize downtime and negotiation pressure. Because the team customized builds per target, each deployment matched the victim’s layout and defenses.

𝗧𝗲𝗰𝗵𝗻𝗶𝗰𝗮𝗹 𝗮𝗻𝗮𝗹𝘆𝘀𝗶𝘀 — 𝗚𝗼-𝗯𝗮𝘀𝗲𝗱 𝗽𝗮𝘆𝗹𝗼𝗮𝗱, 𝗗𝗟𝗟 𝘀𝗶𝗱𝗲𝗹𝗼𝗮𝗱𝗶𝗻𝗴, 𝗮𝗻𝗱 𝗲𝘃𝗮𝘀𝗶𝗼𝗻

Cephalus shipped a Go-based encryptor that prioritized stealth. First, it disabled key defenses (for example, real-time protection), removed shadow copies, and terminated backup-critical services. Next, it used DLL sideloading abusing trusted executables to execute payloads under a legitimate process. Finally, it combined 𝗔𝗘𝗦-𝗖𝗧𝗥 with 𝗥𝗦𝗔 for speed and control while masking the real key schedule with a decoy 𝗔𝗘𝗦 key during analysis.

𝙋𝙚𝙧-𝙩𝙖𝙧𝙜𝙚𝙩 𝙘𝙪𝙨𝙩𝙤𝙢𝙞𝙯𝙖𝙩𝙞𝙤𝙣 𝙖𝙣𝙙 𝙠𝙚𝙮 𝙢𝙖𝙣𝙞𝙥𝙪𝙡𝙖𝙩𝙞𝙤𝙣

Because the operators tuned builds to each environment, the encryptor aligned to the victim’s paths and services. Moreover, the binary obfuscated cryptographic material by XOR-transforming values to evade simple memory inspection. As a result, triage that relies on quick string scans or naïve sandboxing missed the true keys.

𝗟𝗲𝗮𝗸 𝘀𝗶𝘁𝗲𝘀 𝗮𝗻𝗱 𝗽𝗿𝗲𝘀𝘀𝘂𝗿𝗲 𝘁𝗮𝗰𝘁𝗶𝗰𝘀 — 𝗴𝗼𝗳𝗶𝗹𝗲/𝗱𝗹𝗲𝗮𝗸 𝗹𝗶𝗻𝗸𝘀 𝗶𝗻 𝗿𝗮𝗻𝘀𝗼𝗺 𝗻𝗼𝘁𝗲𝘀

Cephalus raised stakes by embedding links to stolen data directly in ransom notes. Because proof-of-theft appears upfront, victims face tangible disclosure risk. Therefore, incident leaders must assume data exposure and coordinate legal, communications, and partner notifications alongside technical containment.

𝘼𝙛𝙛𝙚𝙘𝙩𝙚𝙙 𝙨𝙘𝙤𝙥𝙚 𝙖𝙣𝙙 𝙤𝙥𝙚𝙧𝙖𝙩𝙞𝙣𝙜 𝙥𝙖𝙩𝙩𝙚𝙧𝙣

Victims spanned multiple industries with exposed or mismanaged RDP. Because multi-factor authentication (MFA) remained absent in many environments, the adversaries reused purchased or brute-forced credentials and advanced quickly. Meanwhile, the team adopted pragmatic tradecraft credential replay, living-off-the-land where possible, then a reliable encrypt-and-extort finish.

𝗗𝗲𝘁𝗲𝗰𝘁𝗶𝗼𝗻 𝗮𝗻𝗱 𝘃𝗮𝗹𝗶𝗱𝗮𝘁𝗶𝗼𝗻 — 𝘁𝗿𝗮𝗰𝗲 𝘁𝗵𝗲 𝘀𝘁𝗲𝗽𝘀 𝗮𝗿𝗼𝘂𝗻𝗱 𝙍𝘿𝙋 𝙖𝙣𝙙 𝙋𝙍𝙔

Start with identity telemetry: impossible travel into RDP, first-time admin sessions from consumer ISPs, and sudden creation of high-privilege local users. Then, review endpoint logs for service stops (backup, VSS), real-time-protection changes, and execution of signed binaries that load unexpected DLLs. Afterwards, pivot to egress and storage: spikes to file-sharing providers, new leak-site beacons, and unusual DNS linked to sideloaded processes. Because mailbox rules and file-share audits often reveal data staging, responders should hunt those artifacts in parallel.

𝗠𝗶𝘁𝗶𝗴𝗮𝘁𝗶𝗼𝗻 𝗮𝗻𝗱 𝗵𝗮𝗿𝗱𝗲𝗻𝗶𝗻𝗴 — 𝗥𝗗𝗣 𝘄𝗶𝘁𝗵 𝗽𝗵𝗶𝘀𝗵𝗶𝗻𝗴-𝗿𝗲𝘀𝗶𝘀𝘁𝗮𝗻𝘁 𝗠𝗙𝗔, 𝗼𝗮𝘂𝘁𝗵 𝗰𝗼𝗻𝘀𝗲𝗻𝘁 𝗴𝘂𝗮𝗿𝗱𝗿𝗮𝗶𝗹𝘀, 𝗮𝗻𝗱 𝗕𝗖𝗗𝗥

Enforce phishing-resistant MFA for all remote access, restrict RDP to VPN with device health checks, and rate-limit plus geo-limit logons. Next, block unsolicited third-party app consent and require approvals for elevated scopes. Then, harden backups: isolate, test restore paths, and prevent tamper on VSS. Finally, monitor for signed-binary abuse and DLL sideloading by tracking child-process trees of trusted executables.

𝙄𝙣𝙘𝙞𝙙𝙚𝙣𝙩 𝙧𝙚𝙨𝙥𝙤𝙣𝙨𝙚 𝙥𝙧𝙞𝙤𝙧𝙞𝙩𝙞𝙚𝙨 (𝙠𝙚𝙥𝙩 𝙗𝙞𝙛𝙪𝙧𝙘𝙖𝙩𝙚𝙙, 𝙣𝙤𝙣-𝙡𝙞𝙨𝙩𝙮)

Contain remote access first: disable exposed RDP, rotate credentials, and invalidate active sessions. Because the actors customized builds, collect full memory and disk images from impacted hosts. Then, verify backups and rehearse recovery before wide restores. Afterwards, coordinate legal and communications for data-leak implications.

𝗙𝗔𝗤𝗦

𝙒𝙝𝙮 𝙙𝙤 𝙍𝘿𝙋 𝙘𝙧𝙚𝙙𝙚𝙣𝙩𝙞𝙖𝙡𝙨 𝙠𝙚𝙚𝙥 𝙛𝙖𝙞𝙡𝙞𝙣𝙜 𝙙𝙚𝙛𝙚𝙣𝙨𝙚𝙨?
Because exposed endpoints and weak MFA policies allow commodity tools to replay or brute-force logons. Therefore, move RDP behind VPN, enforce phishing-resistant MFA, and reduce attack surface.

𝙃𝙤𝙬 𝙙𝙤 𝙄 𝙘𝙖𝙩𝙘𝙝 𝘿𝙇𝙇 𝙨𝙞𝙙𝙚𝙡𝙤𝙖𝙙𝙞𝙣𝙜 𝙬𝙞𝙩𝙝𝙤𝙪𝙩 𝙛𝙡𝙤𝙤𝙙𝙞𝙣𝙜 𝙎𝙊𝙘?
Track trusted parent processes that load unsigned or unexpected DLLs, baseline command-line patterns, and alert on mismatched binary-to-DLL directories.

𝙒𝙝𝙖𝙩 𝙝𝙪𝙧𝙩𝙨 𝙧𝙖𝙣𝙨𝙤𝙢𝙬𝙖𝙧𝙚 𝙥𝙚𝙧𝙨𝙞𝙨𝙩𝙚𝙣𝙘𝙚 𝙦𝙪𝙞𝙘𝙠𝙡𝙮?
Disable lateral RDP, remove unauthorized remote-access tools, tighten admin rights, and monitor for mailbox-rule creation that signals data-theft staging.