Vidar Stealer: Forensic Reverse-Engineering & Architectural Dossier

{
  "compiler": "Microsoft Visual C/C++ (MSVC 2017/2019/2022) with static C runtime (/MT)",
  "runtime": "Win32 Native API with dynamic library loading",
  "binary_footprint": "Single native PE32 binary, typically 140 KB - 320 KB uncompressed",
  "stub_size": "212,992 bytes (typical unpacked sample)",
  "packer_obfuscation": "Commercial crypters (e.g., PureCrypter, SmokeLoader) or custom stack string obfuscation",
  "subsystem": "Windows GUI (Subsystem 2)",
  "entry_point_flow": "Entry -> Decrypt Dead-Drop URLs -> Query Social Profiles -> Parse Backend C2 IP:Port -> Query C2 for Configuration -> Download Auxiliary DLLs (sqlite3.dll, nss3.dll) -> Harvest Credentials -> Archive to %ProgramData% -> Exfiltrate via HTTP POST -> Download Tasks -> Terminate",
  "technical_summary": "Vidar Stealer is a native C++ information stealer evolved from the Arkei stealer codebase. It is known for its resilient Dead-Drop Resolver (DDR) architecture, querying legitimate third-party platforms (Telegram channels, Steam community profiles, Mastodon accounts) to dynamically recover active C2 backend IP addresses. Vidar retrieves auxiliary SQLite and NSS libraries dynamically from its C2 server during runtime to harvest browser databases without bundling bulky parsing dependencies."
}

{
  "interface_type": "Web Administration Panel (PHP/MySQL)",
  "builder_tabs_options": [
    {
      "tab": "Dead-Drop Resolver Config",
      "options": [
        "Telegram Channel URLs: Comma-separated list of public Telegram channel bios containing delimited IP strings",
        "Steam Community Profiles: URLs to Steam profiles displaying backend IPs in summary bio",
        "Mastodon / Social Accounts: URLs to social profile descriptions with marker tags (e.g., '|194.26.29.112:80|')"
      ]
    },
    {
      "tab": "Stealer Tasking",
      "options": [
        "Browser Flags: Passwords, Cookies, History, Autofill, Credit Cards",
        "Crypto Wallets: Multi-selection of 40+ desktop wallet paths and browser extension folders",
        "File Grabber: Path specifications, filename filters, and maximum file size threshold (e.g., Desktop\\*.txt:50)",
        "Downloader Rules: Executable drop URLs and execution triggers"
      ]
    }
  ],
  "config_struct_layout": [
    {
      "offset": "0x0000",
      "field": "DdrUrls",
      "type": "char[512]",
      "description": "XOR-encrypted array of dead-drop resolver social URLs"
    },
    {
      "offset": "0x0200",
      "field": "FallbackC2",
      "type": "char[128]",
      "description": "Direct fallback backend IP:Port string"
    },
    {
      "offset": "0x0280",
      "field": "CampaignTag",
      "type": "char[32]",
      "description": "Operator tracking and campaign identifier"
    }
  ],
  "payload_generation_flags": [
    "Architecture: x86 Native",
    "Runtime Linking: Static (/MT)",
    "Symbol Stripping: Complete"
  ],
  "operator_commands": [
    "ConfigString: Server responds to beacon with delimited module configuration (e.g., '1,1,1,1,1,1,1,1,1,1,Desktop\\*.txt:50:')",
    "TaskingDirective: C2 instructs Vidar to download and execute secondary malware binaries"
  ],
  "interface_telemetry_analysis": "The Vidar web administration panel displays real-time infection feeds, log archives grouped by campaign tags, geolocation distribution maps, and search interfaces allowing operators to query stolen logs for specific domain credentials or cryptocurrency keywords."
}

struct Vidar_Stealer_Config {
    uint32_t magic;
    char c2_host[128];
    uint16_t port;
    char install_path[260];
    char mutex[64];
    uint8_t aes_key[32];
};

{
  "injection_chain": "Native execution from memory or dropped staging location; downloads external helper libraries (sqlite3.dll, nss3.dll, freebl3.dll, mozglue.dll) directly into %ProgramData% or %TEMP% and dynamically loads them via LoadLibraryA and GetProcAddress.",
  "ntapi_functions": [
    "kernel32!LoadLibraryA",
    "kernel32!GetProcAddress",
    "kernel32!CreateProcessW",
    "crypt32!CryptUnprotectData",
    "wininet!InternetOpenA",
    "wininet!InternetConnectA",
    "wininet!HttpOpenRequestA",
    "wininet!HttpSendRequestA"
  ],
  "process_hollowing_target": "N/A (Executes within originating process context)",
  "persistence_mechanics": [
    "Non-persistent execution model; harvests credentials, exfiltrates archive, and immediately executes self-deletion routine via cmd.exe"
  ],
  "evasion_hooks": [
    "Dynamic retrieval of dependent DLLs from C2 to avoid static AV signature matching on embedded SQLite/NSS libraries",
    "Obfuscation of API strings and file system search paths"
  ],
  "anti_analysis": [
    "Querying computer name and username against sandbox blacklists (e.g., 'SANDBOX', 'VIRUS', 'MALWARE')",
    "Evaluation of screen dimensions and running process counts (< 25 processes)",
    "Verification of sleep execution timing to detect accelerated sandbox environments"
  ]
}

Concrete technical breakdown of functional modules implemented in the Vidar Stealer binary:

{
  "framing": "Standard HTTP/1.1 GET and POST transactions over port 80/443",
  "serialization": "Plaintext delimited configuration strings from C2; multipart/form-data upload for exfiltrated ZIP archives",
  "handshake": "Client queries Dead-Drop Resolver URLs (Telegram, Steam) -> Extracts backend IP string between delimiter tokens (e.g., '|194.26.29.112:80|') -> Issues HTTP POST to backend with client ID -> C2 returns module config -> Client downloads auxiliary DLLs -> Client uploads ZIP via HTTP POST",
  "cryptography": "Unencrypted HTTP or TLS transport layer encryption; inner payload archives are plain ZIP files containing individual text files and stolen database copies",
  "packet_types": [
    {
      "header": "GET /<channel_name>",
      "payload": "HTTP request to Telegram/Steam social profile",
      "direction": "Client -> Social Platform"
    },
    {
      "header": "POST /<campaign_id>",
      "payload": "Client check-in beacon containing hardware UUID",
      "direction": "Client -> C2"
    },
    {
      "header": "HTTP 200 OK",
      "payload": "Delimited configuration string (e.g., 1,1,1,1,1,Desktop\\*.txt:50:)",
      "direction": "C2 -> Client"
    },
    {
      "header": "POST /<campaign_id>",
      "payload": "Multipart form upload containing ZIP archive with information.txt and credential stores",
      "direction": "Client -> C2"
    }
  ],
  "traffic_signature": "Initial outbound HTTPS traffic to legitimate domains (t.me, steamcommunity.com) followed by direct outbound HTTP POST requests to raw IP addresses transmitting multipart ZIP files."
}

Indicators of compromise and forensic patterns recorded across laboratory triage: