Users of the Instagram mobile app are vulnerable to having their accounts hijacked by a user sharing the same local area network, or LAN, according to security researcher Carlos Reventlov.
A hacker using the same LAN as the victim could spoof the Address Resolution Protocol, tricking the victim’s mobile device into routing traffic through the attacker’s computer. When the victim performs an Instagram action that requires authetication but isn’t sent through an HTTPS server, a plain text cookie would be sent to the hacker’s machine. With the cookie, the hacker can log in to the victim’s account.
To improve security, the cookie should be encrypted.
Reventlov notified Facebook of the issue three weeks ago and has received just an automated reply.