The SMS Alert WordPress plugin before 3.9.8 does not bind its "mobile verified" session flag to...

The SMS Alert WordPress plugin before 3.9.8 does not bind its "mobile verified" session flag to the phone number that was actually verified: after an attacker verifies an OTP sent to their own phone, the signup/login handler reads a fresh, attacker-supplied phone number to select the account and logs them in. An unauthenticated attacker can therefore log in as any user, including an administrator, who has a billing phone on file.