Malicious Office (OOXML) / .XLSM — malware analysis report

Static analysis result for SHA-256 77d6239a1082b6df…

MALICIOUS

Office (OOXML) / .XLSM

145.5 KB Created: 2020-12-01 17:52:01 UTC Authoring application: Microsoft Excel 14.0300
MD5: 0dc402a72f0a963d5ab34f2981ad75ef SHA-1: 88ba0830634d1e2ddb1189731ce6e7e30a62bda5 SHA-256: 77d6239a1082b6dfc5ad9d1c07fcc9610ed933195067e112a0947cb8c149b5d5
492 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1218.011 System Binary Proxy Execution: Regsvr32 T1027 Obfuscated Files or Information

The sample is an XLSM file containing VBA macros that execute upon opening. The Auto_Open macro constructs and executes a PowerShell command. This command decodes a Base64 string which, when interpreted, instructs regsvr32 to download and execute a DLL from the URL http://lyncidscover.2bunny.com/Autodiscover/scrobj.dll. This behavior is consistent with a downloader malware.

Heuristics 13

  • Shell() call in VBA critical OLE_VBA_SHELL
    Shell() call in VBA
  • PowerShell reference in VBA critical OLE_VBA_PS
    PowerShell reference in VBA
  • VBA Base64-decoded Shell command stager critical OLE_VBA_BASE64_SHELL_COMMAND_STAGER
    VBA auto-exec macro decodes Base64 string literals into command or script-launch text and executes the result with Shell. This catches cmd/cscript/PowerShell/VBS launchers hidden from plain keyword matching.
  • ClamAV: Win.Downloader.Regsvr32Unregister-6335678-1 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Win.Downloader.Regsvr32Unregister-6335678-1
  • ClamAV detection on extracted artifact critical EXTRACTED_FILE_CLAMAV
    ClamAV flagged at least one file extracted from inside this sample. Even when the wrapping document carries no AV detection of its own, a hit on the carved artifact is a strong indicator the sample is a delivery vehicle.
  • AutoOpen macro high OLE_VBA_AUTOOPEN
    AutoOpen macro
  • Workbook_Open macro high OLE_VBA_WBOPEN
    Workbook_Open macro
  • Auto_Open macro high OLE_VBA_AUTO
    Auto_Open macro
  • VBA p-code auto-exec with execution tokens high OLE_VBA_PCODE_AUTOEXEC_EXEC
    Compiled VBA/cache stream contains an auto-execution token together with shell/download/object-execution tokens. This catches p-code-only or source-extraction-failure macro documents where visible source is unavailable.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains a VBA project — VBA macros present
  • Environ() call (env variable access) low OLE_VBA_ENVIRON
    Environ() call (env variable access)
  • Suspicious extracted artifact info EXTRACTED_FILE_STATIC_TRIAGE
    One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL http://www.w3.org/1999/02/22-rdf-syntax-ns#
    • http://ns.adobe.com/exif/1.0/

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
efe3cb59ffd6fafe74d4419203f813374963a5d5324054ffe44d807c49f632a7		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 2149 bytes
vbaProject_00.bin
d53a81a005fb556910101d3a82d704c4fa240157c8b8c36e4285f6fb1fa42168		 vba-project OOXML VBA project: xl/vbaProject.bin 23552 bytes
Detection
ClamAV: Win.Downloader.Regsvr32Unregister-6335678-1
Obfuscation or payload: likely
Carved artifact contains 1 long base64-like blob(s).

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