High-Severity Cisco DoS Flaw Plagues Small-Business Switches

Cisco is warning of a high-severity flaw that could allow remote, unauthenticated attackers to cripple several of its popular small-business switches with denial of service (DoS) attacks.

The vulnerability stems from the IPv6 packet processing engine in the switches. IPv6 (also known as Internet Protocol version 6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification system for computers on networks and routes traffic across the Internet.

The flaw (CVE-2020-3363), which has a CVSS score of 8.6 out of 10, is due to insufficient validation of incoming IPv6 traffic.

“An attacker could exploit this vulnerability by sending a crafted IPv6 packet through an affected device,” said Cisco in its Wednesday advisory. “A successful exploit could allow the attacker to cause an unexpected reboot of the switch, leading to a DoS condition.”

Cisco switches affected by this flaw include: 250 Series Smart Switches, 350 Series Managed Switches, 350X Series Stackable Managed Switches, 550X Series Stackable Managed Switches. These switch lineups range in functionality and price, but all were released between 2015 and 2016, and all are web-managed, entry-level devices intended for small businesses.  Updates are available for these products in Release 2.5.5.4.7.

Also affected by the flaw are three series of switches that have reached the end-of-software-maintenance milestone, meaning they will not receive patches. Those are: Small Business 200 Series Smart Switches, Small Business 300 Series Managed Switches and Small Business 500 Series Stackable Managed Switches. It’s not the first time that end of life (EoL) has stopped Cisco from issuing patches for these specific switches when they were vulnerable. In July, Cisco warned that it wasn’t issuing firmware updates in the three switches to address a high-severity flaw that could allow remote, unauthenticated attackers to access the switches’ management interfaces with administrative privileges.

The Cisco Product Security Incident Response Team (PSIRT) said it is not aware of any public announcements or malicious use of the vulnerability. This flaw specifically affects IPv6 traffic – IPv4 traffic (the IP that IPv6 replaced) is not affected, said Cisco.

“Cisco has released software updates that address this vulnerability for devices that have not reached the end of software maintenance,” Cisco said. “There are no workarounds that address this vulnerability.”

Beyond this flaw, Cisco fixed three other high-severity vulnerabilities, with a slew of Thursday security advisories.

One of those is a similar vulnerability in the IPv6 implementation of Cisco StarOS. Cisco StarOS is a virtualized software architecture that spans the ASR (Aggregation Services Routers) 5000 Series. This flaw (CVE-2020-3324) also stems from insufficient validation of incoming IPv6 traffic and could enable an unauthenticated, remote attacker to launch a DoS attack on affected devices.

Another high-severity flaw (CVE-2020-3411) in Cisco’s DNA Center software could allow an unauthenticated remote attacker access to sensitive information on impacted systems. The Cisco DNA Center is a network controller and management dashboard, with integrated tools for network management, automation, virtualization, analytics, security and internet of things (IoT) connectivity.

A final flaw (CVE-2020-3433) plugged by Cisco on Wednesday exists in the AnyConnect Secure Mobility Client for Windows, Cisco’s unified security endpoint agent that delivers security services to protect the enterprise. The flaw exists in the interprocess communication (IPC) channel and could allow an authenticated, local attacker to perform an attack called DLL hijacking, where attackers exploit Windows applications search and load Dynamic Link Libraries.

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