Office (OOXML) / .XLSX malware analysis — malicious · c2880873a9fa9e09

MALICIOUS

Office (OOXML) / .XLSX

125.0 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300

MD5: f34c429e68f39a3c1b65950d3aa2b98f SHA-1: ada0cffe9f6b08869e7a9482923f0b308b149d8d SHA-256: c2880873a9fa9e0988c780f624ea8f023b9fc285f7512cef3e709f2377180748

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an XLSX file containing multiple Excel 4.0 macro sheets, as indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The ClamAV detection 'Xls.Downloader.GreenOffice01223-9937701-0' strongly suggests a downloader functionality. Although the macro content is truncated and obfuscated, the presence of macro sheets and the downloader detection point to an attack pattern where the macros are used to fetch and execute additional malicious content. No specific URLs or executable payloads were directly extracted from the provided script excerpts.

Heuristics 3

Excel 4.0 macro sheet (8 sheet(s)) critical OOXML_XLM_MACROSHEET

Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
XLSB international XLM macro sheet hidden in .xlsx critical OOXML_XLSB_INTL_MACROSHEET_IN_XLSX

OOXML package is named .xlsx but contains XLSB workbook parts and an international Excel 4.0 macro sheet. This hides XLM macro execution from scanners that trust the extension or only inspect XML worksheet parts. The technique is macro execution, not a document-parser CVE.
ClamAV: Xls.Downloader.GreenOffice01223-9937701-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Xls.Downloader.GreenOffice01223-9937701-0

Extracted artifacts 8

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `4be865fd99cf252a0d9292df6f9b6b847dce5f89794eba2f39c31b1a2763d6bb`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2125 bytes
`xlm_sheet_01.bin` `e296f2661d5201bcd027cded81b962b184563d9b9e16833ac2b90da47453f605`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	428 bytes
`xlm_sheet_02.bin` `92b48ebc71415177387c629e42d5920a80724eb19c01f9a6c41221dcdd24c20f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	428 bytes
`xlm_sheet_03.bin` `f21549aa5e6b6c2960b342bb480ff6dfa65dd312754ef1eb0d2547088504ef56`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet3.bin	428 bytes
`xlm_sheet_04.bin` `e307e991028fecd952b05c7d6d1da1b295486d57f601515e097898d852f1a1f1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet4.bin	428 bytes
`xlm_sheet_05.bin` `371f3260d9ae90eddd3f710b3b54b2e62a8faaf17da318ebf3524f364677e89a`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet5.bin	428 bytes
`xlm_sheet_06.bin` `6a04cb0ed4ec0a1e8031ed983ae1600915c967cc73f4dc254df534a62f2fd8a4`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet6.bin	428 bytes
`xlm_sheet_07.bin` `b9467a0dcf66be7c8ff6e1eb2df090f484b30aa99d10acd7256c13d46be04059`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet7.bin	428 bytes

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