Cisco has released its twice-yearly set of security updates for its switches and routers.

There are six advisories in all, each one covering a different component of the Cisco Internetwork Operating System (IOS), which powers the routers. They cover IOS components such as Cisco's VPN software, the Session Initiation Protocol (SIP), and Internet Group Management Protocol, and Network Address Translation (NAT) software.

Released Wednesday, the updates fix 12 bugs. An attacker could possibly leverage some of them to crash the router, Cisco says.

Cisco releases these large bundles of IOS security patches on preset dates, twice a year, to make it easier for network administrators to plan their updates.

The next set of patches is due March 23.