Office (OOXML) / .XLSX malware analysis — malicious · 0f445558df4103ac

MALICIOUS

Office (OOXML) / .XLSX

20.4 KB Created: 2021-08-23 07:21:53 UTC Authoring application: Microsoft Excel 15.0300

MD5: 504d3c19d9721fa65e8b72b66bec00e5 SHA-1: 745260436f8dd487d8c761dfa346fdc8c081ce69 SHA-256: 0f445558df4103ac24d165c3fa8b6529613f28eaf1d4125970be21154de8b58c

384 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File T1140 Deobfuscate or Obfuscate

The XLSX file contains a Workbook_Open macro that utilizes WScript.Shell and CreateObject to execute obfuscated VBA code. This code appears to download a second-stage payload from the URL 'https://brightcarbon.com/' and likely attempts to establish persistence via a Run key entry such as 'HKCU\Software\Microsoft\Windows\CurrentVersion\Run\IAccessible2Proxy'. The obfuscated nature of the shell command and the use of auto-execution routines indicate a malicious intent to compromise the user's system.

Heuristics 10

Shell() call in VBA critical OLE_VBA_SHELL

Shell() call in VBA
WScript.Shell usage critical OLE_VBA_WSCRIPT

WScript.Shell usage
Obfuscated VBA Shell command with URL critical OLE_VBA_OBFUSCATED_SHELL_URL

VBA macro invokes Shell with command text assembled through decoder or string-manipulation functions and includes a URL. This is a high-confidence downloader/dropper pattern, stronger than Shell or URL evidence on their own.
Obfuscated auto-exec VBA loader critical OLE_VBA_OBFUSCATED_AUTOEXEC_LOADER

Auto-exec VBA reconstructs strings with a heavy custom decoder (numeric char-array, repeated hex-string decode, or junk-token Replace removal) and feeds them to a COM-instantiation or execution sink. This obfuscated-loader shape keeps CreateObject/Shell/URL indicators out of the macro source.
Workbook_Open macro high OLE_VBA_WBOPEN

Workbook_Open macro
CreateObject call high OLE_VBA_CREATEOBJ

CreateObject call
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
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 https://brightcarbon.com/

Extracted artifacts 2

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`macros.bas` `b90491180e6fcfc6d61ba7af77f8a24c704ea95a8be9c10b29f4e16334a9f454`	vba-macro	oletools.olevba.extract_macros (decoded VBA source from OOXML)	8595 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 8 long base64-like blob(s).
`vbaProject_00.bin` `7cc2564fda4b8b23073b1cbcc6a5a4be0817af33241f9a72a2dbb21ec50b6905`	vba-project	OOXML VBA project: xl/vbaProject.bin	29184 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 8 long base64-like blob(s).

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