According to advisories from CERT and the UK National Infrastructure Security Co-ordination Centre (NISCC), the vulnerability is in versions of TCP that comply with the Internet Engineering Task Force's TCP specification.
Holes in the widely used internet protocol, if exploited, could be used to terminate TCP sessions, causing denial-of-service effects.
"The exploitation of this vulnerability could have affected the glue that holds the internet together," said Roger Cummings, director for NISCC. "This is important to everyday users, along with companies and government departments that provide the critical national infrastructure."
The flaw can also lead to disrupttions in active sessions between routers. Border Gateway Protocol (BGP), one of the most widely used routing protocols, is particularly vulnerable to the hole, the report said.
Security researcher Paul Watson will be present a paper on the subject at the CanSecWest conference in Vancouver this month.
Industry specialists have been aware of the vulnerability for nearly 20 years, but the hole has grown bigger with the wide adoption of the internet.