chimera

[Content by Gemini 2.5]

Windows File Names: *.chimera
Community Label: “Chimera” or, historically, “Chimera First Variant”

============================================================================

TECHNICAL BREAKDOWN

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: The definitive marker after encryption is “.chimera” (in lower-case).
    • Renaming Convention:
    – Original file Document.docx becomes Document.docx.chimera.
    – Directory names remain intact; folders are never renamed.
    – Inside every affected folder Chimera also drops a ransom note file:
    YOUR_FILES_ARE_ENCRYPTED.HTML and a duplicate YOUR_FILES_ARE_ENCRYPTED.TXT.
    – These notes do NOT share the “.chimera” suffix, so they are easy to spot by their unchanged extension.

  2. Detection & Outbreak Timeline
    • First public sighting: 07-July-2015 (Germany/Austria – German-language e-mails).
    • Initial spike: 14-Jul-2015 (malspam campaign pushing fake résumé attachments).
    • Activity levels fell sharply in Dec-2015 after the master RSA key of the first version was published by a cooperative affiliate, but copy-cat strains using the same branding re-appeared sporadically during 2016–2017.

  3. Primary Attack Vectors
    • Malspam Phishing Campaigns (≈ 90 % of incidents)
    – ZIP attachments laced with .SCR or .JS droppers.
    – Lures: “job application”, “invoice”, or “ScanKB2982791.exe” disguised as a Windows KB patch.
    • RDP/TS (Terminal Services) brute force ≥ 8 %
    – Attackers scanned 3389/TCP for weak administrator passwords, then installed Chimera manually.
    • EternalBlue/DoublePulsar exploit bundles (2017 re-sprays)
    – Second-wave Chimera offshoots bundled the EternalBlue SMB exploit to propagate after initial foothold.

============================================================================

REMEDIATION & RECOVERY STRATEGIES

  1. Prevention (Still Effective Today)
    • Disable Windows Script Host (WSH) on endpoints if not required—Chimera JS droppers die silently.
    • Local Group Policy: Deny execution of wscript.exe, cscript.exe, mshta.exe.
    • Disable SMBv1 across the network (EternalBlue patch surface).
    • Implement E-mail filtering to strip .JS/.SCR/.VBS attachments at the gateway.
    • Segment critical file shares; never map them as persistent drive letters on workstations.
    • Enforce strong RDP/TS passwords & 2-factor auth; place RDS over VPN only.

  2. Infection Cleanup
    Step-by-Step (Windows environments)

  3. Physically isolate the infected machine: cut off Wi-Fi/Ethernet.

  4. Boot into Safe Mode w/ Networking or WinRE → delete the malware file (common names: Chimera.exe, services_update.exe, or %TEMP%\[8 random hex].exe).

  5. Remove registry persistence:
    • Check HKCU\Software\Microsoft\Windows\CurrentVersion\Run and system services that point to the dropped EXE path.

  6. Patch CVE-2012-1723, CVE-2014-100155 (Java), CVE-2015-5122 (Flash) & disable any Java browser plug-in < Java 8u60.

  7. (Re)Scan with an up-to-date AV/EDR engine (HitmanPro, Kaspersky RDS Rescue, ESET MVPs) to be certain.

  8. File Decryption & Recovery
    • Recovery Feasibility – Good News:
    The original Chimera author accidentally leaked the embedded private RSA-2048 master key on 07-Jan-2016. That key fully decrypts all data locked by the first wave (AES-CBC-256 key material wrapped by RSA-2048).
    • Available Tool Chain
    – Official decryptor by Trend Micro & Intel Security (McAfee) – ChimeraDecryptor.exe v1.9 (requires .NET 4.0).
    – Stand-alone Python utility from “bdarnell & herdprotect” – download chimera_decrypter.py script for Linux offline machines.
    • How to Use the Trend/McAfee tool

  9. Run on a CLEAN system (never on the still-infected machine).

  10. Point the tool at a top-level folder or drive letter that contains encrypted *.chimera files.

  11. Drag-and-drop one original/uncorrupted file together with its encrypted twin so the tool can confirm the AES key session.

  12. Click “Start Decryption”; if the key hashes match, it takes ~2–3 GB per hour depending on I/O.
    • Limitations
    – Tool only functions against the 2015/early-2016 campaign.
    – Post-Jan-2017 derivative campaigns changed encryption and now use a fresh RSA public key; for those later samples the OLD KEY is useless and decryption is currently impossible (no second leak yet). Victims can test with the free decryptor—incorrect key add will yield an error message instead of corrupting data.

  13. Other Critical Information
    • Unique Behaviours vs. Other Families
    – Chimera threatens to publish victims’ files to Pastebin if ransom is not paid. However the original author never executed the threat; the warning text is still present in the ransom note.
    – Uses Tor-to-clearnet gateways (6ml2klrnt47b, qkjrmddogd) in ransom notes—malicious domains are now sink-holed but traffic still hitting dead IPs can be used for incident correlation.
    – Chronologically, it was one of the first “extortionware” campaigns claiming a “cloud-backup dump” threat, paving the way for later extortion schemes.

• Broader Impact
– Catalyst for watershed German-language spear-phishing awareness by BSI (Federal Office for Information Security) in Q3-2015.
– Expanded adoption of automated SMB inventory scripts inside German MSSP incident-response playbooks.

============================================================================

REFERENCE LINKS & CHECKSUMS

✓ ChimeraDecryptor.exe Trend Micro SHA-256: 8348e9126450cd17c5ee704a9e1cad031751e1a9fcae965e2e54beedf549b4ae
✓ BSI Alert Meldung “Schadsoftware Chimera” (DE): https://www.bsi.bund.de/EN/Topics/IT-Security/Security-Warnings/Chimera
✓ EternalBlue SMBv1 patch roll-up: KB4012598 (non contradicts 2015, 2016, 2017).