SynopsisThe remote device is missing a vendor-supplied security patch.
DescriptionAccording to its self-reported version and configuration, the Cisco Adaptive Security Appliance (ASA) software running on the remote device is affected by a heap overflow condition in the CIFS (Common Internet Filesystem) code within the Clientless SSL VPN functionality due to improper validation of user-supplied input. An authenticated, remote attacker can exploit this, via a specially crafted URL, to cause the device to reload or the execution of arbitrary code.
Note that only traffic directed to the affected system can be used to exploit this issue, which affects systems configured in routed firewall mode only and in single or multiple context mode. A valid TCP connection is needed to perform the attack. Furthermore, the attacker would need to have valid credentials to log in to the Clientless SSL VPN portal. This vulnerability can be triggered by IPv4 or IPv6 traffic.
SolutionUpgrade to the relevant fixed version referenced in Cisco security advisory cisco-sa-20170208-asa.
Alternatively, as a workaround, it is possible to block an offending URL using a webtype access list, which can be performed using the following steps :
1. Configure the webtype access list :
access-list bugCSCvc23838 webtype deny url https://<asa_ip_address>/+webvpn+/CIFS_R/* access-list bugCSCvc23838 webtype permit url https://* access-list bugCSCvc23838 webtype permit url cifs://*
2. Apply the access list in the group policy with the 'filter value <webtype_acl_name>' command :
group-policy Clientless attributes webvpn filter value bugCSCvc23838