Browser-Only Ransomware: From LLM Hallucinations to a Practical Attack Technique

MITRE Techniques

• [T1204.002 ] User Execution: Malicious File – The attack depends on the victim clicking a lure and approving folder access, as described in ‘the user opens a web page that promises to enhance a photo’ and ‘after user approval’.
• [T1566.002 ] Phishing: Spearphishing Link – A fake AI image-enhancement webpage is used as the lure, described as ‘a fake photo-processing application’ and ‘a Discord avatar AI upscaler’.
• [T1027 ] Obfuscated Files or Information – The malicious intent is hidden behind a benign-looking AI utility and browser workflow, as in ‘disguised as a Discord avatar AI upscaler’ and ‘a convincing AI upscaler interface with hidden ransomware-like behaviors’.
• [T1056.001 ] Input Capture: Keylogging – The generated sample included keylogging logic, described as routines and stubs for ‘keylogging’ and ‘the keylogger observes keystrokes only while the user interacts with the page’.
• [T1113 ] Screen Capture – The code referenced screenshots, described as routines and stubs for ‘screenshots’ and ‘the “desktop screenshot” routine captures the rendered web page’.
• [T1119 ] Automated Collection – The sample attempted to collect multiple data types automatically, including ‘Discord-token collection, crypto-wallet and payment-card discovery, geolocation requests’ and local-file access.
• [T1552.001 ] Unsecured Credentials: Credentials In Files – The sample targeted stored tokens and payment data, described as ‘Discord-token collection’ and ‘payment-card discovery’.
• [T1083 ] File and Directory Discovery – The browser code could enumerate selected folders, as shown by ‘recursive traversal of a user-selected directory’ and ‘enumerate local files in the selected folder’.
• [T1005 ] Data from Local System – The page could read local files after permission was granted, described as ‘reading selected files through browser file handles’ and ‘read files and folders from the local device’.
• [T1041 ] Exfiltration Over C2 Channel – The sample was intended to send stolen file contents to a backend server, described as ‘sending file contents to the Flask backend’ and ‘read and exfiltrate their contents’.
• [T1486 ] Data Encrypted for Impact – The attack goal was to encrypt files and prevent recovery, described as ‘encrypt and overwrite them’ and ‘leaves the user unable to recover the original content’.
• [T1490 ] Inhibit System Recovery – The flow aimed to make recovery difficult by overwriting originals, described as ‘encrypt and overwrite them’ and ‘unable to recover the original content’.
• [T1547.001 ] Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder – The sample included a persistence concept, described as ‘persistence’ and ‘service worker registration attempt’ in browser storage terms.
• [T1105 ] Ingress Tool Transfer – The browser-side workflow delivered malicious functionality through web content and backend routes, described as a ‘Python Flask application that serves victim-facing HTML and JavaScript’.