Bad things came in threes for Cisco security users this week, as the vendor announced vulnerabilities in three of its security hardware products that could lead to denial-of-service attacks on the devices. Meanwhile, a fourth vulnerability in Cisco's IOS-based intrusion-prevention software could allow attackers to evade detection when going after the aforementioned security gear.
Cisco's widely used stand-alone PIX Firewall, Firewall Services Module (FWSM) for switches and routers, and Adaptive Security Appliance (ASA) are vulnerable to receiving a wide variety of doctored packets, which could result in a DoS attack on the products. Additionally, Cisco's IOS-based Intrusion Prevention System (IPS) feature has a flaw which could allow hackers to chop up the malicious packets to evade IPS detection when attacking a Cisco PIX, ASA or other network devices.
Cisco has released new software versions for these devices which fix these vulnerabilities.
The malformed packet vulnerabilities in the PIX and ASA boxes and the FWSM (used in the Catalyst 6500 and 7500 router) include several types of traffic, such as HTTP and SHTTP requests, Session Initiation Protocol (SIP) messages, TCP packets, SNMP requests, and other types of network management and authentication traffic.
Cisco says attackers can overwhelm the vulnerable Cisco devices with these traffic types, causing the equipment to become unresponsive. The company says the attack methods can be done remotely, without any authentication privileges or administrative access to the affected devices.
Adding circularity to the issue is the fact that PIX, ASA and FWSM devices are only vulnerable to being reset by these malformed packets if the security gear is configured to detect these types of malformed packets. Only malformed TCP packet inspection (and SIP inspection in some cases) is enabled by default in PIX, ASA and FWSM gear. If inspection of SIP, HTTP and other traffic types is not present, the devices are safe -- but the rest of the network could be vulnerable.
Before the fixed software can be installed, Cisco says users can thwart these attacks with a number of safeguards, including configuration changes, the use of IPS signatures, and in some cases, deactivating inspection for the types of malformed packets being sent. With the HTTP, SIP and SNMP vulnerabilities, for example, Cisco says it has an attack signature for its Secure IPS product which can stop these attacks.
Cisco also suggests deactivating SIP traffic inspection on an ASA or PIX, or in the case of SNMP, deactivating the service on devices where it is not necessary.
While Cisco says its Secure IPS product can thwart many of the vulnerabilities in ASA, PIX and the FWSM blade, the vendor's software-based IPS technology has a separate flaw attackers could exploit in order to slip their malicious packets to other vulnerable devices.
Cisco calls this a Fragmented Packet Evasion Vulnerability. "By fragmenting malicious network traffic, it may be possible to evade detection by IPS signatures which utilize regular expressions to identify attacks," the company says in an advisory.
This vulnerability is only in the IPS feature in IOS -- a features that gives switches and routers running IOS the ability to detect unwanted traffic. Cisco says users can create special access control lists which prevent the fragmented malicious packets from entering a network.