# 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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