An out-of-bounds write vulnerability [CWE-787] and a Stack-based Buffer Overflow [CWE-121] in FortiOS & FortiProxy captive portal may allow an inside attacker who has access to captive portal to execute arbitrary code or commands via specially crafted HTTP requests.

Workaround:

Set a non form-based authentication scheme:

config authentication schemeedit schemeset method methodnextend

Where <method> can be any of those :

ntlm NTLM authentication.basic Basic HTTP authentication.digest Digest HTTP authentication.negotiate Negotiate authentication.fsso Fortinet Single Sign-On (FSSO) authentication.rsso RADIUS Single Sign-On (RSSO) authentication.ssh-publickey Public key based SSH authentication.cert Client certificate authentication.saml SAML authentication

None of the enabled authentication schemes should be form-based.

Please note that only devices with captive portal enabled are affected.