Cisco IOS Software Release, 15.1(2)T is affected by a DoS vulnerability during the TCP establishment phase.
The vulnerability could cause embryonic TCP connections to remain in a SYNRCVD or SYNSENT state. Enough embryonic TCP connections in these states could consume system resources and prevent an affected device from accepting or initiating new TCP connections, including any TCP-based remote management access to the device.
No authentication is required to exploit this vulnerability. An attacker does not need to complete a three-way handshake to trigger this vulnerability. Therefore, this this vulnerability can be exploited using spoofed packets and may be triggered by normal network traffic.
Cisco has released Cisco IOS Software Release 15.1(2)T0a to address this vulnerability.