{
	"id": "199b72c3-fb85-4ca7-b86f-42baceeac2d2",
	"created_at": "2026-04-06T00:17:44.567472Z",
	"updated_at": "2026-04-10T13:12:43.692144Z",
	"deleted_at": null,
	"sha1_hash": "53e44cdf8842d31fa926794922630773cc28f414",
	"title": "XLSB Files: Because Binary is Stealthier Than XML - SANS ISC",
	"llm_title": "",
	"authors": "",
	"file_creation_date": "0001-01-01T00:00:00Z",
	"file_modification_date": "0001-01-01T00:00:00Z",
	"file_size": 364691,
	"plain_text": "XLSB Files: Because Binary is Stealthier Than XML - SANS ISC\r\nBy SANS Internet Storm Center\r\nArchived: 2026-04-05 14:49:00 UTC\r\nIn one of his last diaries[1], Brad mentioned an Excel sheet named with a .xlsb extension. Now, it was my turn to\r\nfind one... What's the magic behind this file extension? \"XLS\" means that we are facing an Excel sheet and \"B\"\r\nmeans that we have a binary workbook file. Within the current Microsoft office files format, data are stored in\r\nXML. In this case, they are stored in binary. For Microsoft Office, to open a normal or binary file is the same...\r\nbut for an attacker, the plus-value is the increased level of obfuscation! Indeed, it's more difficult to extract\r\ninteresting information like... strings!\r\nWhen you open the file, you see a classic message asking you to enable macros:\r\nLet's have a look at the document:\r\nremnux@remnux:/MalwareZoo/20220324$ oledump.py luamccsbuaraeos.xlsb\r\nWarning: no OLE file was found inside this ZIP container (OPC)\r\nNo VBA macro found! Let's check the content of the file and look for a potential Excel 4 macro:\r\nremnux@remnux:/mnt/hgfs/MalwareZoo/20220324$ zipdump.py luamccsbuaraeos.xlsb\r\nIndex Filename Encrypted Timestamp\r\n 1 [Content_Types].xml 0 1980-01-01 00:00:00\r\nhttps://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/\r\nPage 1 of 4\n\n2 _rels/.rels 0 1980-01-01 00:00:00\r\n 3 xl/_rels/workbook.bin.rels 0 1980-01-01 00:00:00\r\n 4 xl/workbook.bin 0 1980-01-01 00:00:00\r\n 5 xl/worksheets/sheet1.bin 0 1980-01-01 00:00:00\r\n 6 xl/worksheets/sheet2.bin 0 1980-01-01 00:00:00\r\n 7 xl/worksheets/sheet3.bin 0 1980-01-01 00:00:00\r\n 8 xl/worksheets/sheet4.bin 0 1980-01-01 00:00:00\r\n 9 xl/macrosheets/intlsheet1.bin 0 1980-01-01 00:00:00\r\n 10 xl/macrosheets/sheet1.bin 0 1980-01-01 00:00:00\r\n 11 xl/macrosheets/sheet2.bin 0 1980-01-01 00:00:00\r\n 12 xl/theme/theme1.xml 0 1980-01-01 00:00:00\r\n 13 xl/media/image1.png 0 1980-01-01 00:00:00\r\n 14 xl/styles.bin 0 1980-01-01 00:00:00\r\n 15 xl/drawings/drawing1.xml 0 1980-01-01 00:00:00\r\n 16 xl/worksheets/_rels/sheet1.bin.rels 0 1980-01-01 00:00:00\r\n 17 xl/worksheets/_rels/sheet2.bin.rels 0 1980-01-01 00:00:00\r\n 18 xl/worksheets/_rels/sheet3.bin.rels 0 1980-01-01 00:00:00\r\n 19 xl/worksheets/_rels/sheet4.bin.rels 0 1980-01-01 00:00:00\r\n 20 xl/macrosheets/_rels/intlsheet1.bin.rels 0 1980-01-01 00:00:00\r\n 21 xl/macrosheets/_rels/sheet1.bin.rels 0 1980-01-01 00:00:00\r\n 22 xl/macrosheets/_rels/sheet2.bin.rels 0 1980-01-01 00:00:00\r\n 23 xl/drawings/_rels/drawing1.xml.rels 0 1980-01-01 00:00:00\r\n 24 xl/sharedStrings.bin 0 1980-01-01 00:00:00\r\n 25 xl/worksheets/binaryIndex1.bin 0 1980-01-01 00:00:00\r\n 26 xl/worksheets/binaryIndex2.bin 0 1980-01-01 00:00:00\r\n 27 xl/worksheets/binaryIndex3.bin 0 1980-01-01 00:00:00\r\n 28 xl/worksheets/binaryIndex4.bin 0 1980-01-01 00:00:00\r\n 29 xl/macrosheets/binaryIndex1.bin 0 1980-01-01 00:00:00\r\n 30 xl/macrosheets/binaryIndex2.bin 0 1980-01-01 00:00:00\r\n 31 xl/macrosheets/binaryIndex3.bin 0 1980-01-01 00:00:00\r\n 32 xl/printerSettings/printerSettings1.bin 0 1980-01-01 00:00:00\r\n 33 xl/printerSettings/printerSettings2.bin 0 1980-01-01 00:00:00\r\n 34 xl/calcChain.bin 0 1980-01-01 00:00:00\r\n 35 docProps/core.xml 0 1980-01-01 00:00:00\r\n 36 docProps/app.xml 0 1980-01-01 00:00:00\r\nAs you can see, no XML files but \".bin\" files but some streams disclose the presence of macros:\r\nxl/macrosheets/sheet1.bin\r\nxl/macrosheets/_rels/intlsheet1.bin.rels\r\nxl/sharedStrings.bin\r\nsharedStrings.bin is a very good indicator! Let's dump it:\r\nremnux@remnux:/MalwareZoo/20220324$ zipdump.py luamccsbuaraeos.xlsb -s 24 -a | more\r\n00000000: 9F 01 08 17 00 00 00 17 00 00 00 13 07 00 01 00 ................\r\nhttps://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/\r\nPage 2 of 4\n\n00000010: 00 00 58 00 13 07 00 01 00 00 00 64 00 13 07 00 ..X........d....\n00000020: 01 00 00 00 22 00 13 07 00 01 00 00 00 3A 00 13 ....\"........:..\n00000030: 07 00 01 00 00 00 3D 00 13 07 00 01 00 00 00 2C ......=........,\n00000040: 00 13 07 00 01 00 00 00 5C 00 13 07 00 01 00 00 ........\\.......\n00000050: 00 43 00 13 07 00 01 00 00 00 41 00 13 07 00 01 .C........A.....\n00000060: 00 00 00 2E 00 13 07 00 01 00 00 00 4C 00 13 07 ............L...\n00000070: 00 01 00 00 00 26 00 13 07 00 01 00 00 00 28 00 .....\u0026........(.\n00000080: 13 07 00 01 00 00 00 55 00 13 07 00 01 00 00 00 .......U........\n00000090: 2D 00 13 07 00 01 00 00 00 29 00 13 07 00 01 00 -........)......\n000000A0: 00 00 54 00 13 07 00 01 00 00 00 52 00 13 07 00 ..T........R....\n000000B0: 01 00 00 00 45 00 13 07 00 01 00 00 00 4E 00 13 ....E........N..\n000000C0: D9 01 00 6A 00 00 00 22 00 68 00 22 00 26 00 22 ...j...\".h.\".\u0026.\"\n000000D0: 00 74 00 74 00 70 00 22 00 26 00 22 00 73 00 3A .t.t.p.\".\u0026.\".s.:\n000000E0: 00 2F 00 2F 00 6D 00 61 00 22 00 26 00 22 00 6E ././.m.a.\".\u0026.\".n\n000000F0: 00 61 00 22 00 26 00 22 00 72 00 65 00 22 00 26 .a.\".\u0026.\".r.e.\".\u0026\n00000100: 00 22 00 73 00 74 00 61 00 22 00 26 00 22 00 75 .\".s.t.a.\".\u0026.\".u\n00000110: 00 72 00 61 00 22 00 26 00 22 00 6E 00 74 00 22 .r.a.\".\u0026.\".n.t.\"\n00000120: 00 26 00 22 00 65 00 2E 00 63 00 22 00 26 00 22 .\u0026.\".e...c.\".\u0026.\"\n00000130: 00 6F 00 6D 00 2F 00 44 00 6E 00 22 00 26 00 22 .o.m./.D.n.\".\u0026.\"\n00000140: 00 69 00 35 00 22 00 26 00 22 00 4C 00 36 00 46 .i.5.\".\u0026.\".L.6.F\n00000150: 00 22 00 26 00 22 00 4D 00 4C 00 22 00 26 00 22 .\".\u0026.\".M.L.\".\u0026.\"\n00000160: 00 65 00 56 00 22 00 26 00 22 00 32 00 2F 00 4E .e.V.\".\u0026.\".2./.N\n00000170: 00 68 00 22 00 26 00 22 00 66 00 6E 00 76 00 22 .h.\".\u0026.\".f.n.v.\"\n00000180: 00 26 00 22 00 68 00 2E 00 70 00 6E 00 22 00 26 .\u0026.\".h...p.n.\".\u0026\n00000190: 00 22 00 67 00 22 00 2C 00 22 00 13 DF 01 00 6D .\".g.\".,.\".....m\n000001A0: 00 00 00 22 00 68 00 22 00 26 00 22 00 74 00 22 ...\".h.\".\u0026.\".t.\"\n000001B0: 00 26 00 22 00 74 00 70 00 22 00 26 00 22 00 73 .\u0026.\".t.p.\".\u0026.\".s\nWe have URLs:\nhxxps://manarestaurante[.]com/Dni5L6FMLeV2/Nhfnvh.png\nhxxps://hondadominicana[.]com/vAXoUmZFeV2B/Nhfnvh.png\nhxxps://shlokahujafilms[.]com/Xz6RyJCaHMP/Nhfnvh.png\nProbably, the macro will loop across the three URLs and try to fetch the next stage. The payload is a DLL file.\nLike in Brad's diary, it's a Qakbot[2] sample!\nIf you would like to have a look at the macro, the easiest way is to open the XLSB file in Excel and save it as an\nXLSM file. You don't need to activate macros to perform this operation but do this always in a sandbox.\nNow, you'll be able to address the file as usual:\nremnux@remnux:/MalwareZoo/20220324$ zipdump.py luamccsbuaraeos.xlsm -s 4 -d | xmldump.py pretty\n?xml version=\"1.0\" ?\u003e\nhttps://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/\nPage 3 of 4\n\nNUEVD!$F$1 In conclusion, we have now a new file extension to keep an eye on! These XLSB files have interesting\nfeatures[3]...\n[1] https://isc.sans.edu/forums/diary/Qakbot+infection+with+Cobalt+Strike+and+VNC+activity/28448\n[2] https://malpedia.caad.fkie.fraunhofer.de/details/win.qakbot\n[3] https://analystcave.com/excel-working-with-large-excel-files-the-xlsb-format/\nXavier Mertens (@xme)\nXameco\nSenior ISC Handler - Freelance Cyber Security Consultant\nPGP Key\nSource: https://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/\nhttps://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/\nPage 4 of 4",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"Malpedia"
	],
	"origins": [
		"web"
	],
	"references": [
		"https://isc.sans.edu/forums/diary/XLSB+Files+Because+Binary+is+Stealthier+Than+XML/28476/"
	],
	"report_names": [
		"28476"
	],
	"threat_actors": [],
	"ts_created_at": 1775434664,
	"ts_updated_at": 1775826763,
	"ts_creation_date": 0,
	"ts_modification_date": 0,
	"files": {
		"pdf": "https://archive.orkl.eu/53e44cdf8842d31fa926794922630773cc28f414.pdf",
		"text": "https://archive.orkl.eu/53e44cdf8842d31fa926794922630773cc28f414.txt",
		"img": "https://archive.orkl.eu/53e44cdf8842d31fa926794922630773cc28f414.jpg"
	}
}