Sagemcom F@ST 5280 Privilege Escalation

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# Exploit Title: Sagemcom router insecure deserialization > privilege  
escalation  
# Date: 08-31-2020  
# Exploit Author: Ryan Delaney  
# Author Contact: ryan.delaney () owasp org  
# Author LinkedIn: https://www.linkedin.com/in/infosecrd/  
# Vendor Homepage: https://sagemcom.com/en  
# Software Link: N/A (F@ST 5280 firmware not published)  
# Version: F@ST 5280 router, F/W 1.150.61, possibly others  
# Tested on: F@ST 5280 router, F/W 1.150.61  
# CVE: CVE-2020-24034  
  
1. Description  
  
Sagemcom F@ST 5280 routers using firmware version 1.150.61,  
and possibly others, have an insecure deserialization vulnerability  
that allows any authenticated user to perform a privilege escalation  
to any other user. By making a request with valid sess_id, nonce,  
and ha1 values inside of the serialized session cookie, an attacker may  
alter the user value inside of this cookie, and assume the role and  
permissions of the user specified. By assuming the role of the user  
'internal', which is inaccessible to end users by default, the attacker  
gains the permissions of the 'internal' account, which includes the  
ability to flash custom firmware to the router, allowing the attacker  
to achieve a complete compromise.  
  
Note that the 'internal' account is disabled and hidden by default, and the  
primary administrative account ('admin'), lacks the permission to  
flash custom firmware to the device, meaning that an attacker  
exploiting this vulnerability obtains access exceeding that of  
the legitimate, authorized system administrator.  
  
2. Proof of Concept  
  
Log in as a valid user (default is admin:admin). Retrieve the 'session'  
cookie. Simply change the only occurrence of the string "admin" within  
the cookie to "internal", and make a new request with this modified cookie.  
If you decode the cookie, you will note this is the 4th key value pair  
inside of the cookie, where the key is "user", and the value is "admin".  
  
3. Solution  
  
This vulnerability is only exploitable with a valid existing session.  
Changing the administrative password to a strong, non-default value,  
and ensuring that TLS certificate has the correct fingerprint will  
help prevent attackers from obtaining a valid existing session.  
  
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