A programming slip in Cisco VPN software has introduced a critical vulnerability hitting ten different Adaptive Security Appliance and Firepower Threat Defense Software products.
The bug scores a perfect ten CVSS rating, and is present in the products' SSL VPN functionality. That's bad news because if you've deployed the VPN – specifically, webvpn – for staff to use in the field, the interface will be exposed to the Internet. If you're lucky, an attacker may just trigger a reload and denial-of-service attack. If you're unlucky, the miscreant will be able to execute arbitrary evil code on your network firewall.
From Switchzilla's advisory: “The vulnerability is due to an attempt to double free a region of memory when the webvpn feature is enabled on the Cisco ASA device. An attacker could exploit this vulnerability by sending multiple, crafted XML packets to a webvpn-configured interface on the affected system.”
The problem affects the 3000 series of industrial firewalls, the ASA 5500 and 5500-X firewalls, a firewall module for Catalyst 6500 switches and 7600 Series routers, the virtual ASA 1000V and ASAv products, three Firepower appliances (2100, 4110, and the 9300 ASA module), and the Firepower Thread Defense (FTD) Software.
The programming flaw appears to have been introduced at least as far back as ASA 8.x, which was released five or so years ago. Cisco has published a table of affected ASA builds and the patched versions in the aforementioned advisory. The bug also affects Firepower Threat Defense 6.2.2, which was released last year, and later versions up to the fixed release, 188.8.131.52-4 or 184.108.40.206-6 depending on your hardware.
Fixes for both the Adaptive Security Appliance software and Firepower Threat Defense software are available – if you have a Cisco service contract, or your reseller can provide the patches. If not, you'll have to ask the Cisco Technical Assistance Center really nicely. ®