Over the past two days, numerous security advisories have been issued regarding an apparent vulnerability in the Transmission Control Protocol (TCP). TCP is used by most computers, routers, and other network hardware for network/Internet communication.
The specific vulnerability can lead to a denial of service attack; according to the UK's National Infrastructure Security Co-ordination Centre, "If exploited, the vulnerability could allow an attacker to create a Denial of Service condition against existing TCP connections, resulting in premature session termination." Such an attack could be more significant if it was used to interrupt Border Gateway Protocol (BGP) sessions, which could interrupt network traffic on affected routers.
According to the advisories, individual vendors will need to amend their implementations of TCP in order to prevent such attacks.
The actual vulnerability was apparently discovered a few months ago; however, the person who discovered the vulnerability will be disclosing the full details of the exploit today (Thursday), leading security experts and government agencies to issue advisories beforehand.